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Texas Instruments Selecting the Right Texas Instruments Signal Switch Application notes
Application Report
SZZA030 - October 2001
Selecting the Right Texas Instruments Signal Switch
John Perry and Chris Cockrill
Standard Linear & Logic
ABSTRACT
Texas Instruments offers a wide variety of electronic switches (digital, analog, bilateral,
bilateral analog) in a variety of families, including CBT, CBTLV, HC, LV, and LVC. Depending
on the application, the right solution may be an analog switch that passes digital signals, or
vice versa. This application report summarizes the various switching technologies and
provides application considerations for choosing the appropriate TI signal switch.
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Single FET Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Analog (Bilateral) Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Analog Versus Digital Signal Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Application Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.1 Digital Signal Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.2 Digital Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.3 Analog Signal Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.4 Analog Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.5 SN74CBT Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4.6 CD74HCT Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.7 CD74HC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.8 SN74HC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4.9 CD4066B Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.10 LV-A Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.4.11 LVC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.4.12 CBTLV Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.1 CBT3125 as a Gain-Control Circuit [for VI < (VCC – 2 V)] With LMV321 . . . . . . . . . . . . . . . . . 40
3.2 LVC4066A T-Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3 LVC1G66 TTL-to-LVTTL Level Shifter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Trademarks are the property of their respective owners.
1
SZZA030
Appendix A Test Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A.1 ron Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A.2 VO vs VI Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A.3 Frequency-Response Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
A.4 Crosstalk Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
A.5 Charge-Injection Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
A.6 Feedthrough Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
A.7 Sine-Wave and Total-Harmonic-Distortion Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
A.8 Crosstalk-Between-Switches Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
List of Figures
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
2
Ideal Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Simplified CMOS (FET) Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
N-Channel FET Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
On-State Resistance vs Lowest I/O Voltage for an n-Channel FET Switch With VCC = 5 V . . . . . 7
Parallel n-/p-Channel FET Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
On-State Resistance vs Input Voltage for a Parallel n-/p-Channel FET Switch . . . . . . . . . . . . . . . . 8
Log ron vs VI, VCC = 5 V (SN74CBT3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
ron vs VI, VCC = 5 V (SN74CBT3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
VI vs VO, VCC = 5 V (SN74CBT3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
VI vs VO, VCC = 5 V (CD74HCT4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
ron vs VI, VCC = 5 V (CD74HCT4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
VI vs VO, VCC = 4.5 V (CD74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
ron vs VI, VCC = 4.5 V (CD74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
VO vs VI, VCC = 6 V (CD74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ron vs VI, VCC = 6 V (CD74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
VO vs VI, VCC = 9 V (CD74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
ron vs VI, VCC = 9 V (CD74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
VO vs VI, VCC = 2 V (SN74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
ron vs VI, VCC = 2 V (SN74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
VO vs VI, VCC = 4.5 V (SN74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
ron vs VI, VCC = 4.5 V (SN74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
VO vs VI, VCC = 6 V (SN74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
ron vs VI, VCC = 6 V (SN74HC4066) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
VO vs VI, VCC = 5 V (CD4066B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
ron vs VI, VCC = 5 V (CD4066B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
VO vs VI, VCC = 10 V (CD4066B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
ron vs VI, VCC = 10 V (CD4066B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Selecting the Right Texas Instruments Signal Switch
SZZA030
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
A–1
A–2
A–3
A–4
A–5
A–6
A–7
A–8
VO vs VI, VCC = 15 V (CD4066B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
ron vs VI, VCC = 15 V (CD4066B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
VO vs VI, VCC = 2 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
ron vs VI, VCC = 2 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
VO vs VI, VCC = 2.5 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
ron vs VI, VCC = 2.5 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
VO vs VI, VCC = 3.3 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
ron vs VI, VCC = 3.3 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
VO vs VI, VCC = 5 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
ron vs VI, VCC = 5 V (SN74LV4066A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
VO vs VI, VCC = 1.8 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
ron vs VI, VCC = 1.8 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
VO vs VI, VCC = 2.5 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
ron vs VI, VCC = 2.5 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
VO vs VI, VCC = 3.3 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
ron vs VI, VCC = 3.3 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
VO vs VI, VCC = 5 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
ron vs VI, VCC = 5 V (SN74LVC1G66) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
VO vs VI, VCC = 2.5 V (SN74CBTLV3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
ron vs VI, VCC = 2.5 V (SN74 CBTLV3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
VO vs VI, VCC = 3.3 V (SN74CBTLV3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
ron vs VI, VCC = 3.3 V (SN74 CBTLV3125) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
CBT3125 Gain-Control Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
LV4066A/LVC2G04 T-Switch Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
LVC1G66 TTL-to-LVTTL Level Shifter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
ron Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
VO vs VI Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Frequency-Response Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Crosstalk (Switch Control to Output) Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Charge-Injection Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Feedthrough Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Sine-Wave and Total-Harmonic-Distortion Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Crosstalk-Between-Switches Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Selecting the Right Texas Instruments Signal Switch
3
SZZA030
List of Tables
1
2
3
4
5
6
7
8
9
10
11
12
13
14
4
TI Switch Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Summary of Digital Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VCC Above 5.5 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VCC = 4.5 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VCC = 3 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
VCC = 2.5 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
SN74CBT3125 Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
CD74HCT4066 Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CD74HC4066 Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
SN74HC4066 Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
CD4066B Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
SN74LV4066A Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
SN74LVC1G66 Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
SN74CBTLV3125 Analog Parameter Measurement Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Selecting the Right Texas Instruments Signal Switch
SZZA030
1
Introduction
Texas Instruments offers a wide variety of signal switches in a variety of families, including CBT,
CBTLV, CD4000, HC, LV-A, and LVC. These signal switches can be digital, analog, bilateral, or
bilateral analog. Selecting the right one can be a formidable task. The purpose of this application
report is to make the selection process easier by illustrating the differences between the families
and removing ambiguity in the naming conventions.
2
Background
When first considering switches, a schematic of the ideal switch (similar to Figure 1) might come
to mind.
I/O
I/O
(In)
(Out)
Signal In = Signal Out
Figure 1. Ideal Switch
An input signal applied to the left I/O pin (or port) in Figure 1 results in an identical output signal
at the right I/O pin, and vice versa. However, in the real world, switches are not ideal and there
always is some loss. In the case of clean, properly working mechanical switches, the loss is so
miniscule that it hardly bears noting.
Like mechanical switches, solid-state switches are not ideal either. In fact, losses associated
with solid-state switches can be significant. Why use a switch like this if it is so far from ideal?
The answer is convenience. Solid-state switches are small, fast, easy to use, easy to control,
and consume relatively little power compared to traditional electrically controlled switches, such
as relays. The switches referred to in this application report are complementary metal-oxide
semiconductor (CMOS) field-effect transistor (FET) switches. As mentioned previously, they are
not ideal, so we need a way to examine and compare the performance characteristics of the
different CMOS families. Figure 2 shows a simplified-circuit model of a CMOS switch.
Selecting the Right Texas Instruments Signal Switch
5
SZZA030
CMOS (FET) Switch
Control or Enable
CF
Ci
ron
I/O
(In)
CioA
I/O
CioB
CCHNL
(Out)
Cio
Cio
Signal In > Signal Out
Figure 2. Simplified CMOS (FET) Switch
The output signal (right side, Figure 2) is altered due to parasitic effects of the switch. Results
may include decreased amplitude, signal distortion, phase shift, the introduction of noise, and
frequency attenuation.
Parameters contributing to the nonideal characteristics include:
•
Ci – Control (enable) pin input capacitance
•
CF – Feedthrough capacitance
•
Cio – Capacitance measured from either the input or output of the switch
•
CCHNL – NMOS (PMOS) channel capacitance
•
ron – On-state resistance from drain to source rds(on) of the pass FET
As mentioned previously, TI offers a variety of CMOS-technology switches. Table 1 summarizes
the families by switch type.
Table 1. TI Switch Technologies
6
TECHNOLOGY
ABBREVIATION
Crossbar
CBT
N-channel FET
CMOS
CD4000
Parallel n-/p-channel FET
High-speed CMOS
HC
Parallel n-/p-channel FET
Low-voltage CMOS
LV-A
Parallel n-/p-channel FET
Low-voltage CMOS
LVC
Parallel n-/p-channel FET
Low-voltage crossbar
CBTLV
Parallel n-/p-channel FET
Selecting the Right Texas Instruments Signal Switch
SWITCH TYPE
SZZA030
Single FET Switch
Figure 3 shows a simplified FET switch, which consists of an n-channel transistor and gate bias
and enable circuitry. The switch is bidirectional; the source and drain are interchangeable (while
operating, the side with the lowest VI/O is the source). TI CBT bus switches are this type.
A
B
Drain
(Source)
VI/O
Source
(Drain)
Gate
VI/O
OE
Figure 3. N-Channel FET Switch
For an n-channel FET to operate properly, the gate should be biased more positive than the
magnitude of the signals to be passed. This is because the on-state resistance, ron (or rDS(on) as
it also is called), increases as the gate, minus source voltage, VGS, decreases. In the case of
CBT, when OE is low, the gate of the FET is biased to near VCC. If the lowest VI/O signal
approaches the magnitude of VCC, VGS decreases and ron increases (see Figure 4). The ability
to maintain a low ron in a FET switch depends on maintaining VGS as large as possible. In many
applications, this characteristic is not a problem, but the designer should be aware of the
nonlinearity of this type of device.
20
ron – Ω
2.1
15
Nominal
10
5
0
–1
0
1
2
3
4
5
VI – V
Figure 4. On-State Resistance vs Lowest I/O Voltage
for an n-Channel FET Switch With VCC = 5 V
Selecting the Right Texas Instruments Signal Switch
7
SZZA030
2.2
Analog (Bilateral) Switches
Analog (or bilateral, as they also are called) switches consist of a single n-channel transistor in
parallel with a single p-channel transistor (see Figure 5).
A
B
VI/O
VI/O
OE
Figure 5. Parallel n-/p-Channel FET Switch
As before, when VI/O approaches VCC, the n-channel conductance decreases (ron increases)
while the p-channel gate-source voltage is maximum and its ron is minimal. The resulting parallel
resistance combination is much flatter than individual channel resistances (see Figure 6).
p-Channel
n-Channel
ron – Ω
20
15
Nominal
10
5
n-Channel || p-Channel
0
–1
0
1
2
3
4
5
VI – V
Figure 6. On-State Resistance vs Input Voltage
for a Parallel n-/p-Channel FET Switch
A flat ron is especially important if VI/O signals must swing from rail to rail. However, the tradeoff
is increased switch capacitance due to the additional p-channel transistor and associated bias
circuitry. TI offers a variety of choices of analog switches: HCT, HC, CD4000, LV-A, LVC, and
CBTLV.
8
Selecting the Right Texas Instruments Signal Switch
SZZA030
Some manufacturers offer n-channel signal switches with charge-pump-enabled pass
transistors. A design of this type allows the gate voltage to be higher than VCC. This increases
VGS above what is possible in noncharge-pump devices and allows signals at or above VCC to
be passed. A switch of this type has the advantage of low, relatively flat ron (over the signal
range), without the addition of a p channel and while maintaining Cio values comparable to pure
n-channel FET switches. This performance comes at the expense of increased ICC (from a few
µA to several mA in some cases).
2.3
Analog Versus Digital Signal Switches
TI offers a wide variety of signal switches, and sometimes the nomenclature can be confusing to
the point of implying limited functionality for a device or family. In reality, a switch, is a switch, is
a switch (well, almost):
•
Digital switch. Designed to pass (or isolate) digital signal levels. May exhibit the capability to
satisfactorily pass analog signals. Examples are CBT and CBTLV switch families.
•
Analog switch. Designed to pass (or isolate) analog signals. Often exhibits good digital signal
performance as well. Examples are CD4066B, CD74HCT4066, CD74HC4066,
SN74HC4066, SN74LV4066A, and SN74LVC1G66 switches.
•
Bilateral switch. There are two meanings:
–
Signals can be passed in either direction (A to B, or B to A) through the switch.
–
Switch can be used in analog or digital applications.
Examples are CD4066B, CD74HCT4066, CD74HC4066, SN74HC4066, SN74LV4066A, and
SN74LVC1G66 switches.
•
Bus switch. Digital switches designed for multibit switching in computing applications.
Examples are CBT and CBTLV switch families.
The name bus switch implies digital only. However, with better understanding of switch
characteristics, it is apparent that this view of their application might be too limited. Tables 2, 4,
5, 6, 7 and 14 summarize the performance of the CBT3125 and CBTLV3125 quadruple FET bus
switches versus other TI bilateral analog switches. With regard to analog performance, these
bus switches outperformed at least one bilateral switch in every parameter measurement.
It should be apparent that the most important switch characteristic depends on how it is used:
•
What VCC levels are present?
•
What amplitude signals are required to be passed?
•
What is the maximum signal distortion limit for the system?
In the following paragraphs, performance of TI signal switches is summarized to aid in the
selection of the best signal switch for a given application.
Selecting the Right Texas Instruments Signal Switch
9
SZZA030
2.4
Application Considerations
2.4.1
Digital Signal Considerations
•
VCC. There are a number of considerations and tradeoffs here. What voltage levels are
present on the board? What is the amplitude of the signal levels to be passed? Is level
translation required?
•
VIH/VIL. Switch control (Enable). How will the switch be controlled? Logic level output?
Comparator? ASIC? Should the switch turn on if the control signal is high or low?
•
Switch output level. The maximum signal level a switch without a charge pump can pass is
limited to the switch VCC. Is there sufficient noise margin on the device downstream of the
switch such that signal attenuation in the switch will not cause data errors? For instance, the
n-channel transistor of a CBT device clamps the switch output at a little more than 1 V below
the operating VCC, making it unsuitable for 5-V CMOS high-level (VIH = 3.5 V) signal
transmission unless operated from at least 4.5-V VCC.
•
ron.
–
Is the switch connected to a transmission line? If so, what is the impedance? The switch
ron should be less than or equal to the line impedance to allow for proper matching and
to prevent unwanted signal reflections.
–
For nontransmission-line connections, the switch ron and the load resistance form an
undesired voltage divider. In this case, that is a switch with a ron small enough to ensure
the switch output is not reduced below a valid input high level (VIH) for the connected
load. As mentioned previously, the tradeoff for low ron is often higher signal-path
capacitance, which reduces frequency response.
•
ten/tdis. These parameters determine how quickly the switch can respond to a desired on or
off state. In general, switch enable and disable times are not symmetrical. This is not usually
an issue, as few applications require high control (enable) signal frequencies.
•
tpd. This parameter is negligible for all but the most critical timing budgets. When the switch
is on, the propagation delay through the pass transistor(s) is minimal. TI specifies this
number as the mathematical calculation of the typical ron times the load capacitance.
•
Number of bits required to be switched. With TI’s wide variety of signal switches, it is
possible to switch between 1 to 32 bits at the same time with a single device. For instance,
the LVC1G66 or CBT1G125 can be used to switch a single bit, while the CBTLV16211 is
capable of switching 24 bits total in banks of 12. Or, by tying the adjacent enable pins
together, it is possible to control 24 bits with one enable signal.
•
Special features. TI offers bus switches with special features, such as an integrated diode for
single-component level shifting (CBTD), active clamps for undershoot protection (CBTK),
Schottky-diode clamps for undershoot protection (CBTS), a bus-hold option (CBTH) for
holding floating or unused I/O pins at valid logic levels, and an integrated-series-resistor
option (CBTR) to reduce signal-reflection noise.
Table 2 summarizes the digital performance characteristics of eight TI signal switches from
which generalities can be derived regarding switch-family performance. For exact parameters,
refer to the respective data sheets.
10
Selecting the Right Texas Instruments Signal Switch
SZZA030
2.4.2
Digital Performance
Table 2. Summary of Digital Performance†
PARAMETER
CD4066
CD74HC4066
CD74HCT4066
SN74HC4066
LVC1G66
LV4066A
CBT3125
CBTLV3125
VCC
ron
tpd‡
3–18 V
2–10 V
4.5–5.5 V
2–6 V
1.65–5.5V
2–5.5 V
4–5.5 V
2.3–3.6 V
200–1300 Ω
15–142 Ω
25–142 Ω
30–150 Ω
3–30 Ω
21–225 Ω
5–22 Ω
5–40 Ω
7–40 ns
4–90 ns
4–18 ns
3–75 ns
0.6–2 ns
0.3–18 ns
0.25–0.35ns
0.15–0.25 ns
15–70 ns
8–150 ns
4–18 ns
18–225 ns
1.5–10 ns
1.6–32 ns
1.8–5.6 ns
2–4.6 ns
15–70 ns
12–225 ns
9–36 ns
22–250 ns
1.4–10 ns
3.2–32 ns
1–4.6 ns
1–4.2 ns
VIH
(control
inputs)
approx.
0.7 × VCC
5-V CMOS
5-V TTL
5-V CMOS
5-V CMOS
5-V CMOS
5-V TTL/
LVTTL
LVTTL/
2.5-V CMOS
VIL
(control
inputs)
approx.
0.2 × VCC
5-V CMOS
5-V TTL
5-V CMOS
5-V CMOS
5-V CMOS
5-V TTL/
LVTTL
LVTTL/
2.5-V CMOS
Ci (control)
5–7.5 pF
10 pF
10 pF
3–10 pF
2 pF
1.5 pF
3 pF
2.5 pF
8 pF
5 pF
5 pF
9 pF
ten§
tdis¶
Cio (on)
Cio (off)
13 pF
6 pF
5.5 pF
4 pF
7 pF
† Data are based on data-sheet parameters for the parts tested for this application report. Refer to the respective data sheets for specific parameters
and load conditions.
‡ tpd is the same as tPLH/tPHL. The switch contributes no significant propagation delay other than the RC delay of the typical on-state resistance
of the switch and the load capacitance when driven by an ideal voltage source (zero output impedance)
§ ten is the same as tPZL/tPZH.
¶ tdis is the same as tPLZ/tPHZ.
2.4.3
Analog Signal Considerations
•
VCC. For noncharge-pump switches, VCC determines the amplitude of the analog signals that
can be passed without clipping. The gate(s) of the pass transistors must be biased relative to
the minimum and maximum values of the expected input voltage range. Switches, such as
the CD4000 series, allow for biasing from two supplies, making it easy to pass both positive
and negative signals. Switches with integrated charge pumps can elevate the gate voltage
above VCC (at the expense of larger ICC) and, thus, pass signals of a magnitude greater than
VCC.
•
VIH/VIL. Why are these important analog switch considerations? In most applications, the
signal switch is controlled by the output of a digital source, therefore, the control signal
levels, VIH and VIL, must be compatible with that source to ensure proper operation of the
switch. The CD74HC4066 and CD74HCT4066 are excellent examples of switches with
almost exactly the same performance characteristics, but very different control signal levels.
The VIH of the CD74HC4066 is 3.15 V, with VCC at 4.5 V, while CD74HCT4066 is specified
with VIH of 2 V for VCC between 4.5 and 5.5 V.
•
ron. Because it contributes to signal loss and degradation, low ron tradeoffs must be
considered. Noncharge-pump switches achieve low ron with large pass transistors. These
larger transistors lead to larger die sizes and increased Cio. This additional channel
capacitance can be very significant as it limits the frequency response of the switch. As
stated in section 2.4.1, switches utilizing charge-pump technology can achieve low ron and
Cio, but require significantly higher ICC.
Selecting the Right Texas Instruments Signal Switch
11
SZZA030
12
•
Frequency response. All CMOS switches have an upper limit to the frequency that can be
passed. No matter how low ron and Cio can be maintained in the chip manufacturing process,
they still form an undesired low-pass filter that attenuates the switch output signal.
•
Sine-wave distortion or total harmonic distortion. These are measurements of the linearity of
the device. Nonlinearity can be introduced a number of ways (design, device physics, etc.)
but, typically, the largest contributor is ron. As shown in Figures 2 and 4, ron varies with VI/O
for all types of CMOS switches. Having a low ron is important, but a flat ron over the signal
range is almost equally important. N-channel switches, such as CBT, exhibit very flat ron
characteristics for signal ranges of 0 < VI/O < (VCC – 2 V), but ron increases very rapidly as
VI/O approaches VCC and VGS decreases. Parallel n-/p-channel switches offer good ron
flatness for signal ranges of 0 < VI/O < VCC, with the best flatness characteristic at the
highest recommended switch VCC.
•
Crosstalk. There are two types of crosstalk to consider:
–
Control (enable) to output. The level of crosstalk is a measure of how well decoupled the
switch control signal is from the switch output. Due to the parasitic capacitance of CMOS
processes, changing the state on the control signal causes noise to appear on the
output. In audio applications, this can be a source of the annoying pop that is sometimes
heard when switching the unit on or off.
–
Between switches. The level of crosstalk also is a measure of adjacent-channel rejection.
As with control-to-output crosstalk, parasitic capacitance can couple the signal on one
switch with that on another switch.
•
Charge Injection (Q). TI specifies enable-to-output crosstalk and some competitors use this
parameter. As with enable-to-output crosstalk, changing the state on the control pin causes a
charge to be coupled to the channel of the transistor introducing signal noise. It is presented
in this report for a relative comparison with the competition.
•
Feedthrough. This characteristic is related to the ability of the switch to block signals when
off. As with crosstalk, parasitic capacitance allows high frequencies to couple through the
switch, making it appear to be on.
Selecting the Right Texas Instruments Signal Switch
SZZA030
2.4.4
Analog Performance
Table 3. VCC Above 5.5 V†
PARAMETER
ron
(typical to maximum)
CD74HC4066
15–126 Ω
BETTER PERFORMANCE
CD74HC4066‡
30 Ω
CD4066
200–550 Ω
ron (peak)
(typical to maximum)
SN74HC4066‡
50 Ω (typ)
CD74HC4066
not specified
CD4066
not specified
Frequency response
CD74HC4066§
200 MHz
CD4066
40 MHz
SN74HC4066§
30 MHz
THD/Sine wave distortion
THD/Sine-wave
CD74HC4066
0.008%
SN74HC4066§
0.05%
CD4066
0.4%
Crosstalk
(enable to output)
SN74HC4066
20 mV
CD4066
50 mV
CD74HC4066
550 mV
Crosstalk
(between switches)
CD4066
–50 dB at 8 MHz
CD74HC4066§
–72 dB at 1 MHz
SN74HC4066§
–45 dB at 1 MHz
Feedthrough attenuation
CD74HC4066§
–72 dB at 1 MHz
CD4066
–50 dB at 1 MHz
SN74HC4066§
–42 dB at 1 MHz
† Data are based on data-sheet parameters for the parts tested for this application report. Refer to the respective data sheets for
specific parameters and load conditions.
‡ Specification at VCC = 6 V
§ Specification at VCC = 4.5 V
Table 4. VCC = 4.5 V†
PARAMETER
BETTER PERFORMANCE
ron
(typical to maximum)
LVC1G66
3–10 Ω
CBT3125‡
5–15 Ω
LV4066A
21–100 Ω
CD74HC/
HCT4066
25–142 Ω
SN74HC4066
50–106 Ω
CBT3125§
5–1000 Ω
ron (peak)
(typical to maximum)
CBT3125‡§
10 Ω
LVC1G66
6–15 Ω
LV4066A
31–125 Ω
CD74HC/
HCT4066§
50–70 Ω
SN74HC4066
70–215 Ω
CBT3125§
1000 Ω
Frequency response
CBT3125‡§
>200 MHz
LVC1G66
195 MHz
CD74HC/
HCT4066¶
200 MHz
LV4066A
50 MHz
SN74HC4066
30 MHz
THD/Sine wave distortion
THD/Sine-wave
LVC1G66
0.01%
CD74HC/
HCT4066
0.023%
CBT3125‡§
0.035%
SN74HC4066
0.05%
LV4066A
0.1%
Crosstalk
(enable to output)
SN74HC4066
15 mV
LV4066A
50 mV
LVC1G66
100 mV
CBT3125§
120 mV
CD74HCT4066
130 mV
Crosstalk
(between switches)
CD74HC/HCT4066
–72 dB
LVC2G66
–58 dB
CBT3125‡§
–53 dB
SN74HC4066
–45 dB
LV4066A
–45 dB
Feedthrough attenuation
CD74HC/HCT4066
–72 dB
LVC1G66
–58 dB
SN74HC4066
–42 dB
LV4066A
–40 dB
CBT3125§
–36 dB
CD74HC4066
200 mV
† Data are based on data-sheet parameters for the parts tested for this application report. Refer to the respective data sheets for specific parameters
and load conditions.
‡ CBT3125, 0 ≤ VI/O ≤ (VCC – 2 V)
§ Value from application report measurement. Not specified in data sheet.
¶ Ranked here due to load variation from other devices in this report
Selecting the Right Texas Instruments Signal Switch
13
SZZA030
Table 5. VCC = 3 V†
PARAMETER
BETTER PERFORMANCE
ron
(typical to maximum)
LVC1G66
6–15 Ω
CBTLV3125
5–15 Ω
LV4066A
29–190 Ω
CD74HC4066‡
Not specified
SN74HC4066‡
Not specified
ron (peak)
(typical to maximum)
CBTLV3125§
15–20 Ω
LVC1G66
12–20 Ω
LV4066A
57–225 Ω
CD74HC4066‡
Not specified
SN74HC4066‡
Not specified
Frequency response
CBTLV3125§
>200 MHz
LVC1G66
175 MHz
CD74HC4066‡
Not specified
LV4066A
35MHz
SN74HC4066†
Not specified
THD/Sine-wave distortion
LVC1G66
0.015%
CD74HC4066‡
Not specified
SN74HC4066‡
Not specified
CBTLV3125§
0.09%
LV4066A
0.1%
Crosstalk
(enable to output)
SN74HC4066‡
Not specified
LV4066A
20 mV
LVC1G66
70 mV
CBTLV3125§
70 mV
CD74HC4066‡
Not specified
Crosstalk
(between switches)
CD74HC4066‡
Not specified
LVC2G66
–58 dB
CBTLV3125§
–49 dB
SN74HC4066‡
Not specified
LV4066A
–45 dB
Feedthrough attenuation
CD74HC4066‡
Not specified
LVC1G66
–58 dB
CBTLV3125
–52 dB
SN74HC4066‡
Not specified
LV4066A
–40 dB
† Data are based on data-sheet parameters for the parts tested for this application report. Refer to the respective data sheets for specific parameters
and load conditions.
‡ Position in table based on estimated performance. Information not specified in data sheet.
§ Value from application report measurement. Not specified in data sheet.
Table 6. VCC = 2.5 V†
PARAMETER
BETTER PERFORMANCE
ron
(typical to maximum)
LVC1G66
9–20 Ω
CBTLV3125
5–40 Ω
LV4066A
38–225 Ω
CD74HC4066‡
Not specified
SN74HC4066§
150 Ω
ron (peak)
(typical to maximum)
CBTLV3125¶
15–45 Ω
LVC1G66
20–30 Ω
LV4066A
143–600 Ω
CD74HC4066‡
Not specified
SN74HC4066§
320 Ω
Frequency response
CBTLV3125¶
>200 MHz
LVC1G66
120 MHz
CD74HC4066‡
Not specified
LV4066A
30 MHz
SN74HC4066‡
Not specified
THD/Sine-wave distortion
LVC1G66
0.025%
CD74HC4066‡
Not specified
SN74HC4066‡
Not specified
LV4066A
0.1%
CBTLV3125¶
0.11%
Crosstalk
(enable to output)
SN74HC4066‡
Not specified
LV4066A
15 mV
CBTLV3125‡
30 mV
LVC1G66
50 mV
CD74HC4066‡
Not specified
Crosstalk
(between switches)
CD74HC4066‡
Not specified
LVC2G66
–58 dB
CBTLV3125
–45 dB
SN74HC4066‡
Not specified
LV4066A
–45 dB
Feedthrough attenuation
CD74HC4066‡
Not specified
LVC1G66
–58 dB
CBTLV3125
–52 dB
SN74HC4066‡
Not specified
LV4066A
–40 dB
† Data are based on data-sheet parameters for the parts tested for this application report. Refer to the respective data sheets for specific parameters
and load conditions.
‡ Position in table based on estimated performance. Information not specified in data sheet.
§ Data at VCC = 2 V
¶ Value from application report measurement. Not specified in data sheet.
14
Selecting the Right Texas Instruments Signal Switch
SZZA030
SN74CBT Characteristics
10000
ron
1000
100
10
85°C
25°C
–40°C
1
0
1
2
3
4
5
VI
Figure 7. Log ron vs VI, VCC = 5 V (SN74CBT3125)
30
25
20
ron
2.4.5
15
85°C
25°C
10
–40°C
5
0
0
0.5
1
1.5
2
2.5
3
3.5
4
VI
Figure 8. ron vs VI, VCC = 5 V (SN74CBT3125)
Selecting the Right Texas Instruments Signal Switch
15
SZZA030
4.5
–40°C
4
25°C
3.5
85°C
3
VO
2.5
2
1.5
1
0.5
0
0
1
2
3
4
5
VI
Figure 9. VI vs VO, VCC = 5 V (SN74CBT3125)
Table 7. SN74CBT3125 Analog Parameter Measurement Data†
Frequency
Response
VCC
Sine-Wave
Distortion
Total Harmonic
Distortion
Crosstalk
1 kHz
Between Switches
Enable to Output
–53 dB
120 mV
5V
>200 MHz
0.035%
0.15%
† Postcharacterization measurement for SN74CBT3125
2.4.6
Charge
Injection
Feedthrough
g
7.2 pC
–36 dB
CD74HCT Characteristics
5
–55°C
4.5
25°C
4
125°C
3.5
VO
3
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
VI
Figure 10. VI vs VO, VCC = 5 V (CD74HCT4066)
16
Selecting the Right Texas Instruments Signal Switch
5
SZZA030
80
70
60
50
ron
125°C
40
25°C
30
–55°C
20
10
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
VI
Figure 11. ron vs VI, VCC = 5 V (CD74HCT4066)
Table 8. CD74HCT4066 Analog Parameter Measurement Data†
VCC
Frequency
Response
Total Harmonic
Distortion
1 kHz
Crosstalk
Between Switches
4.5 V
200 MHz
0.023%
–72 dB
† Data-sheet values for CD74HCT4066, except as noted
‡ Postcharacterization measurement for CD74HCT4066
‡
Charge
g Injection
j
Feedthrough
g
8.1 pC
–72 dB
Enable to Output
130 mV
Selecting the Right Texas Instruments Signal Switch
17
SZZA030
2.4.7
CD74HC Characteristics
5.0
–55°C
25°C
125°C
4.0
VO
3.0
2.0
1.0
0.0
0
1
2
3
5
4
VI
Figure 12. VI vs VO, VCC = 4.5 V (CD74HC4066)
60.0
50.0
ron
40.0
30.0
125°C
25°C
20.0
–55°C
10.0
0.0
0
1
2
3
4
VI
Figure 13. ron vs VI, VCC = 4.5 V (CD74HC4066)
18
Selecting the Right Texas Instruments Signal Switch
5
SZZA030
6.0
–55°C
25°C
5.0
125°C
3.0
2.0
1.0
0.0
0
1
2
3
4
5
6
VI
Figure 14. VO vs VI, VCC = 6 V (CD74HC4066)
40.0
35.0
30.0
125°C
25.0
25°C
ron
VO
4.0
20.0
–55°C
15.0
10.0
5.0
0.0
0
1
2
3
4
5
6
VI
Figure 15. ron vs VI, VCC = 6 V (CD74HC4066)
Selecting the Right Texas Instruments Signal Switch
19
SZZA030
9.0
–55°C
8.0
25°C
7.0
125°C
6.0
VO
5.0
4.0
3.0
2.0
1.0
0.0
0
1
2
3
4
5
6
7
8
9
VI
Figure 16. VO vs VI, VCC = 9 V (CD74HC4066)
30.0
25.0
125°C
ron
20.0
25°C
15.0
–55°C
10.0
5.0
0.0
0
1
2
3
4
5
6
7
8
9
VI
Figure 17. ron vs VI, VCC = 9 V (CD74HC4066)
Table 9. CD74HC4066 Analog Parameter Measurement Data†
VCC
Frequency
q
y
Response
Total Harmonic Distortion
1 kHz
Between Switches
Crosstalk
Enable to Output
4.5 V
200 MHz
0.022%
–72 dB
9V
200 MHz
0.008%
N/A
† Data-sheet values for CD74HC4066, except as noted
‡ Postcharacterization measurement for CD74HC4066
20
Selecting the Right Texas Instruments Signal Switch
Charge Injection‡
Feedthro gh
Feedthrough
200 mV
6.2 pC
–72 dB
550 mV
9.0 pC
N/A
SZZA030
2.4.8
SN74HC Characteristics
2
–40°C
1.8
25°C
1.6
85°C
1.4
VO
1.2
1
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
VI
Figure 18. VO vs VI, VCC = 2 V (SN74HC4066)
350
300
250
ron
200
150
85°C
25°C
100
–40°C
50
0
0
0.5
1
1.5
2
VI
Figure 19. ron vs VI, VCC = 2 V (SN74HC4066)
Selecting the Right Texas Instruments Signal Switch
21
SZZA030
5
–40°C
25°C
85°C
4
VO
3
2
1
0
0
1
2
3
4
5
VI
Figure 20. VO vs VI, VCC = 4.5 V (SN74HC4066)
80
70
60
85°C
25°C
50
ron
–40°C
40
30
20
10
0
0
0.5
1
1.5
2
2.5
3
3.5
VI
Figure 21. ron vs VI, VCC = 4.5 V (SN74HC4066)
22
Selecting the Right Texas Instruments Signal Switch
4
4.5
SZZA030
7
–40°C
25°C
6
85°C
5
VO
4
3
2
1
0
0
1
2
3
4
5
6
VI
Figure 22. VO vs VI, VCC = 6 V (SN74HC4066)
60
85°C
50
25°C
40
ron
–40°C
30
20
10
0
0
1
2
3
4
5
6
VI
Figure 23. ron vs VI, VCC = 6 V (SN74HC4066)
Selecting the Right Texas Instruments Signal Switch
23
SZZA030
Table 10. SN74HC4066 Analog Parameter Measurement Data†
VCC
Frequency
q
y
Response
Sine-Wave Distortion
1 kHz
Between Switches
Crosstalk
Enable to Output
2V
N/A
N/A
N/A
4.5 V
30 MHz
0.05%
6V
N/A
N/A
Charge Injection‡
Feedthro gh
Feedthrough
N/A
3.8 pC
N/A
–45 dB
15 mV
5.9 pC
–42 dB
N/A
20 mV
7.9 pC
N/A
† Data-sheet values for SN74HC4066, except as noted
‡ Postcharacterization measurement for SN74HC4066
2.4.9
CD4066B Characteristics
5
–55°C
4.5
25°C
4
125°C
3.5
VO
3
2.5
2
1.5
1
0.5
0
0
1
2
3
4
VI
Figure 24. VO vs VI, VCC = 5 V (CD4066B)
24
Selecting the Right Texas Instruments Signal Switch
5
SZZA030
600
500
125°C
400
ron
25°C
300
–55°C
200
100
0
0
1
2
3
4
5
VI
Figure 25. ron vs VI, VCC = 5 V (CD4066B)
10
–55°C
25°C
9
125°C
8
7
VO
6
5
4
3
2
1
0
0
2
4
6
8
10
VI
Figure 26. VO vs VI, VCC = 10 V (CD4066B)
Selecting the Right Texas Instruments Signal Switch
25
SZZA030
300
250
125°C
200
ron
25°C
150
–55°C
100
50
0
0
2
4
6
10
8
VI
Figure 27. ron vs VI, VCC = 10 V (CD4066B)
16
–55°C
25°C
14
125°C
12
VO
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
VI
Figure 28. VO vs VI, VCC = 15 V (CD4066B)
26
Selecting the Right Texas Instruments Signal Switch
SZZA030
200
180
125°C
160
140
25°C
ron
120
100
–55°C
80
60
40
20
0
0
2
4
6
12
10
8
14
16
VI
Figure 29. ron vs VI, VCC = 15 V (CD4066B)
Table 11. CD4066B Analog Parameter Measurement Data†
VCC/VSS
5 V/–5 V
10 V/0 V
Frequency
q
y
Response
Total Harmonic Distortion
1 kHz
Between Switches
Crosstalk
Enable to Output
40 MHz
141 MHz‡
0.04%
0.032%‡
–50 dB at 8 MHz
–75 dB‡
35 mV‡
Charge
g
Injection‡
50 mV
18.8 pC
Feedthro gh
Feedthrough
–50 dB at 1 MHz
–65 dB‡
† Data-sheet values for CD4066B, except as noted
‡ Postcharacterization measurement for CD4066B. Frequency response, THD, crosstalk, and feedthrough measured using load conditions
specified in Appendix A, in order to make a more valid comparison with other devices in this report.
Selecting the Right Texas Instruments Signal Switch
27
SZZA030
2.4.10
LV-A Characteristics
2.5
–40°C
25°C
85°C
2
VO
1.5
1
0.5
0
0.5
0
1.5
1
2
VI
Figure 30. VO vs VI, VCC = 2 V (SN74LV4066A)
400
350
–40°C
300
25°C
ron
250
85°C
200
150
100
50
0
0
0.5
1.5
1
2
VI
Figure 31. ron vs VI, VCC = 2 V (SN74LV4066A)
28
Selecting the Right Texas Instruments Signal Switch
2.5
SZZA030
3
–40°C
25°C
2.5
85°C
1.5
1
0.5
0
0.5
0
1.5
1
2.5
2
3
VI
Figure 32. VO vs VI, VCC = 2.5 V (SN74LV4066A)
100
90
80
70
60
ron
VO
2
50
85°C
40
25°C
30
–40°C
20
10
0
0
0.5
1
1.5
2
2.5
VI
Figure 33. ron vs VI, VCC = 2.5 V (SN74LV4066A)
Selecting the Right Texas Instruments Signal Switch
29
SZZA030
3.5
–40°C
25°C
3
85°C
2.5
VO
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
VI
Figure 34. VO vs VI, VCC = 3.3 V (SN74LV4066A)
60
50
ron
40
85°C
30
25°C
–40°C
20
10
0
0
0.5
1
1.5
2
2.5
3
VI
Figure 35. ron vs VI, VCC = 3.3 V (SN74LV4066A)
30
Selecting the Right Texas Instruments Signal Switch
3.5
SZZA030
5
–40°C
25°C
4
85°C
VO
3
2
1
0
0
1
2
3
4
5
VI
Figure 36. VO vs VI, VCC = 5 V (SN74LV4066A)
30
25
85°C
ron
20
25°C
–40°C
15
10
5
0
0
1
2
3
4
5
VI
Figure 37. ron vs VI, VCC = 5 V (SN74LV4066A)
Selecting the Right Texas Instruments Signal Switch
31
SZZA030
Table 12. SN74LV4066A Analog Parameter Measurement Data†
VCC
Frequency
q
y
Response
Sine-Wave Distortion
1 kHz
Between Switches
Crosstalk
Enable to Output
Charge
g
Injection‡
Feedthro gh
Feedthrough
2.3 V
30 MHz
0.1%
–45 dB
15 mV
2.1 pC
–40 dB
3V
35 MHz
0.1%
–45 dB
20 mV
2.7 pC
–40 dB
4.5 V
50 MHz
0.1%
–45 dB
50 mV
3.0 pC
–40 dB
† Data-sheet values for SN74LV4066A, except as noted
‡ Postcharacterization measurement for SN74LV4066A
2.4.11
LVC Characteristics
2
–40°C
25°C
85°C
VO
1.5
1
0.5
0
0
1
VI
Figure 38. VO vs VI, VCC = 1.8 V (SN74LVC1G66)
32
Selecting the Right Texas Instruments Signal Switch
2
SZZA030
110
90
–40°C
70
ron
25°C
85°C
50
30
10
0
1
2
VI
Figure 39. ron vs VI, VCC = 1.8 V (SN74LVC1G66)
3
–40°C
25°C
2.5
85°C
VO
2
1.5
1
0.5
0
0
1
2
3
VI
Figure 40. VO vs VI, VCC = 2.5 V (SN74LVC1G66)
Selecting the Right Texas Instruments Signal Switch
33
SZZA030
20
ron
15
85°C
10
25°C
–40°C
5
0
0
1
2
3
VI
Figure 41. ron vs VI, VCC = 2.5 V (SN74LVC1G66)
3
–40°C
25°C
2.5
85°C
VO
2
1.5
1
0.5
0
0
1
2
VI
Figure 42. VO vs VI, VCC = 3.3 V (SN74LVC1G66)
34
Selecting the Right Texas Instruments Signal Switch
3
SZZA030
15
10
85°C
ron
25°C
–40°C
5
0
0
2
4
VI
Figure 43. ron vs VI, VCC = 3.3 V (SN74LVC1G66)
6
–40°C
25°C
5
85°C
VO
4
3
2
1
0
0
1
2
3
4
5
6
VI
Figure 44. VO vs VI, VCC = 5 V (SN74LVC1G66)
Selecting the Right Texas Instruments Signal Switch
35
SZZA030
8
85°C
7
25°C
6
ron
5
4
3
–40°C
2
1
0
0
1
2
3
4
5
VI
Figure 45. ron vs VI, VCC = 5 V (SN74LVC1G66)
Table 13. SN74LVC1G66 Analog Parameter Measurement Data†
VCC
Frequency
q
y
Response
Sine-Wave Distortion
1 kHz
10 kHz
Crosstalk
Enable to Output
Charge
g
Injection‡
Feedthro gh
Feedthrough
1.8 V
35 MHz
0.1%
0.15%
35 mV
2.5 pC
–42 dB
2.5 V
120 MHz
0.025%
0.025%
50 mV
3.0 pC
–42 dB
3V
175 MHz
0.015%
0.015%
70 mV
3.3 pC
–42 dB
4.5 V
195 MHz
0.01%
0.01%
100 mV
3.5 pC
–42 dB
† Data-sheet values for SN74LVC1G66, except as noted
‡ Postcharacterization measurement for SN74LVC1G66
36
Selecting the Right Texas Instruments Signal Switch
SZZA030
2.4.12
CBTLV Characteristics
3
–40°C
25°C
85°C
VO
2
1
0
0
1
2
3
VI
Figure 46. VO vs VI, VCC = 2.5 V (SN74CBTLV3125)
12
10
85°C
25°C
ron
8
6
–40°C
4
2
0
0
0.5
1
1.5
2
2.5
3
VI
Figure 47. ron vs VI, VCC = 2.5 V (SN74 CBTLV3125)
Selecting the Right Texas Instruments Signal Switch
37
SZZA030
4
–40°C
25°C
85°C
VO
3
2
1
0
0
1
2
4
3
VI
Figure 48. VO vs VI, VCC = 3.3 V (SN74CBTLV3125)
10
9
8
7
85°C
ron
6
5
25°C
4
–40°C
3
2
1
0
0
1
2
3
VI
Figure 49. ron vs VI, VCC = 3.3 V (SN74CBTLV3125)
38
Selecting the Right Texas Instruments Signal Switch
4
SZZA030
Table 14. SN74CBTLV3125 Analog Parameter Measurement Data†
VCC
Frequency
Response
p
2.5 V
>200 MHz
Sine-Wave
Distortion
Total
Harmonic
Distortion
Crosstalk
Charge
Injection
j
Feedthrough
1 kHz
1 kHz
Between Switches
Enable to Output
0.089%
0.11%
–45 dB
30 mV
12.1 pC
–52 dB
3.3 V
>200 MHz
0.033%
0.09%
† Postcharacterization measurement for CBTLV3125
–49 dB
70 mV
15.5 pC
–52 dB
Selecting the Right Texas Instruments Signal Switch
39
SZZA030
3
Applications
TI signal switches can be configured for numerous applications. Three switches are presented
here for illustrative purposes:
3.1
•
A bus switch in an analog application (digital switch in an analog application)
•
Improvement of off-isolation characteristics with a T configuration
•
Single-bit level shifting with an analog switch (analog switch in a digital application)
CBT3125 as a Gain-Control Circuit [for VI < (VCC – 2 V)] With LMV321
An example of the CBT3125 in a gain-control circuit is shown in Figure 50.
VCC
R1
R2
–
VI
CBT3125
1OE VCC
4OE
1A
4A
1B
4B
2OE
3OE
2A
3A
2B
GND 3B
LMV321
+
R4
R3
1A
R2
2A
R3
1IN+ VCC+
OUT +
VO
+ 1 ) Rø
R ø + ǒR ) r
1B
ron(2)
2B
ron(3)
3B
ron(4)
4B
R
VO
VI
5
1
R5
4A
ron(1)
R5
GND
IN–
3A
R4
LMV321
+
VI
R1
VO
Ǔøǒ
on(1)
R2
)r
Ǔøǒ
on(2)
R3
)r
Ǔøǒ
on(3)
R4
)r
Figure 50. CBT3125 Gain-Control Circuit
By choosing values for R1 through R4, such that RX >> ron(x), the on-state resistance of the
CBT3125 can be ignored. Thus, RII simplifies to:
RII = R1 II R2 II R3 II R4
Because the CBT device uses 5-V TTL switching levels, it can be controlled easily from either
CMOS or TT logic.
40
Selecting the Right Texas Instruments Signal Switch
Ǔ
on(4)
SZZA030
3.2
LVC4066A T-Switch
The series connection doubles the effective switch ron when passing signals, but the tradeoff is
improved off isolation—a key concern when passing high-frequency signals. Feedthrough
attenuation for the LV4066A is specified as –40 dB using a single switch. However, when
connected in a T configuration as shown in Figure 51, isolation in excess of –65 dB was
measured using a 5-V VCC.
T-Switch
CF(1)
CF(2)
ron(1)
ron(2)
VI
1
VO
2
3
ron(3)
CF(3)
C
L
H
LV4066A
IN
OUT
1A
VCC
1B
1B
1C
2B
4C
2A
4A
2C
4B
3C
3B
GND
3A
Switch Position
1, 2 open; 3 closed
1, 2 closed; 3 open
C
LVC3G04
R
C
1A VCC
1Y
3Y
2A
3A
GND 2Y
Figure 51. LV4066A/LVC2G04 T-Switch Configuration
The values of R and C (including PCB resistance and capacitance) are chosen such that the
R || ron(4) × C time constant is faster than the propagation delay through the inverter. This allows
switch 3 to open before switches 1 and 2 close. Conversely, the R × C time constant slows the
transition of the control signal to switch 3, allowing switches 1 and 2 to open before switch 3
closes.
Selecting the Right Texas Instruments Signal Switch
41
SZZA030
3.3
LVC1G66 TTL-to-LVTTL Level Shifter
The LVC1G66 can be used for simple translation from 5-V TTL levels to LVTTL (see Figure 52).
The control pin is tolerant to 5.5 V and, with a maximum ron at VCC = 3.3 V of 15 Ω, the voltage
drop across the switch is only 0.36 V with 24 mA of through current.
3.3 V
LVC1G66
A
VCC
B
GND
C
5-V TTL Signal
Figure 52. LVC1G66 TTL-to-LVTTL Level Shifter
4
Conclusion
Factors that go into selecting a signal switch can be numerous (analog, digital, VCC, ten/tdis,
etc.). This application report has presented the various TI signal-switch technologies (CBT,
CBTLV, CD4000, HC, HCT, LV-A, and LVC), explained TI switch nomenclature, and provided
example applications of switches to aid the designer in selecting the right TI signal switch.
42
Selecting the Right Texas Instruments Signal Switch
SZZA030
Appendix A
A.1
Test Circuits
ron Measurement
VCC
A
VI = VCC or GND
VCC
B
VO
(On)
Control
or Enable
GND
IT
r on
+V
I
– VO
IT
W
V
VI – VO
Figure A–1. ron Test Circuit
A.2
VO vs VI Measurement
VCC
A
VI = 0 to VCC
Control
or Enable
B
VCC
VO
(On)
GND
Figure A–2. VO vs VI Test Circuit
Selecting the Right Texas Instruments Signal Switch
43
SZZA030
A.3
Frequency-Response Measurement
VCC/2
VCC
DEVICE
RL
CL
SN74CBT3125
600 Ω
50 pF
CD74HCT4066
50 Ω
10 pF
CD74HC4066
50 Ω
10 pF
SN74HC4066
CD4066B†
600 Ω
50 pF
1 kΩ
–
CD4066B‡
600 Ω
50 pF
SN74LV4066A
600 Ω
50 pF
SN74LVC1G66
600 Ω
50 pF
600 Ω
50 pF
SN74CBTLV3125
† Data-sheet load
‡ Application-report load
RL
0.1 µF
A
VO
(On)
50 Ω
fin
B
VCC
Control
or Enable
CL
GND
Adjust fin to obtain 0 dBm at output. Increase fin until dB meter reads –3 dB.
Figure A–3. Frequency-Response Test Circuit
A.4
Crosstalk Measurement
VCC/2
DEVICE
RL
CL
SN74CBT3125
600 Ω
50 pF
CD74HCT4066
600 Ω
50 pF
CD74HC4066
600 Ω
50 pF
SN74HC4066
CD4066B†
600 Ω
50 pF
10 kΩ
–
CD4066B‡
600 Ω
50 pF
SN74LV4066A
600 Ω
50 pF
SN74LVC1G66
600 Ω
50 pF
600 Ω
50 pF
SN74CBTLV3125
† Data-sheet load
‡ Application-report load
VCC
Rin =
600 Ω
VCC/2
RL
A
VCC
Control or
Enable
(On)
B
CL
GND
fin
50 Ω
fin = 1 MHz (square wave)
Figure A–4. Crosstalk (Switch Control to Output) Test Circuit
44
Selecting the Right Texas Instruments Signal Switch
VO
SZZA030
A.5
Charge-Injection Measurement
VCC
A
B
VO
VCC
(On)
Control
or Enable
fin
CL = 1 nF
GND
50 Ω
Figure A–5. Charge-Injection Test Circuit
A.6
Feedthrough Measurement
DEVICE
RL
CL
SN74CBT3125
600 Ω
50 pF
CD74HCT4066
50 Ω
10 pF
CD74HC4066
50 Ω
10 pF
SN74HC4066
CD4066B†
600 Ω
50 pF
1 kΩ
–
CD4066B‡
600 Ω
50 pF
SN74LV4066A
600 Ω
50 pF
SN74LVC1G66
600 Ω
50 pF
600 Ω
50 pF
SN74CBTLV3125
† Data-sheet load
‡ Application-report load
VCC/2
VCC/2
VCC
RL
0.1 µF
fin
50 Ω
RL
A
VCC
(Off)
Control
or Enable
B
VO
CL
GND
fin = 1 MHz (sine wave)
Adjust fin to obtain 0 dBm at input.
Figure A–6. Feedthrough Test Circuit
Selecting the Right Texas Instruments Signal Switch
45
SZZA030
A.7
Sine-Wave and Total-Harmonic-Distortion Measurement
DEVICE
RL
CL
SN74CBT3125
10 kΩ
50 pF
CD74HCT4066
10 kΩ
50 pF
CD74HC4066
10 kΩ
50 pF
SN74HC4066
CD4066B†
10 kΩ
50 pF
10 kΩ
–
CD4066B‡
10 kΩ
50 pF
SN74LV4066A
10 kΩ
50 pF
SN74LVC1G66
10 kΩ
50 pF
10 kΩ
50 pF
SN74CBTLV3125
† Data-sheet load
‡ Application-report load
VCC/2
VCC
10 µF
fin
RL
A
10 µF
B
VCC
VO
(On)
600 Ω
Control
or Enable
CL
GND
fin = 1 kHz (sine wave)
Figure A–7. Sine-Wave and Total-Harmonic-Distortion Test Circuit
A.8
Crosstalk-Between-Switches Measurement
DEVICE
RL
CL
SN74CBT3125
600 kΩ
50 pF
CD74HCT4066
50 Ω
10 pF
CD74HC4066
10 kΩ
50 pF
SN74HC4066
CD4066B†
600 kΩ
50 pF
1 kΩ
–
CD4066B‡
600 kΩ
50 pF
SN74LV4066A
600 kΩ
50 pF
SN74LVC2G66
600 kΩ
50 pF
600 kΩ
50 pF
SN74CBTLV3125
† Data-sheet load
‡ Application-report load
VCC/2
VCC
Rin
600 Ω
fin
50 Ω
RL
1A or 1B
1B or 1A
VCC
0.1 µF
Control
or Enable
2A or 2B
Rin
600 Ω
VO(1)
(On)
RL
2B or 2A
(Off)
Control
or Enable
GND
Figure A–8. Crosstalk-Between-Switches Test Circuit
Selecting the Right Texas Instruments Signal Switch
VO(2)
CL
20 log10 [VO(2) VI(1)] or
20 log10 [VO(1) VI(2)]
46
VCC/2
CL
IMPORTANT NOTICE
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enhancements, improvements, and other changes to its products and services at any time and to discontinue
any product or service without notice. Customers should obtain the latest relevant information before placing
orders and should verify that such information is current and complete. All products are sold subject to TI’s terms
and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are used to the extent TI
deems necessary to support this warranty. Except where mandated by government requirements, testing of all
parameters of each product is not necessarily performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for
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