MAX3262 1Gbps, High-Speed Limiting Amplifier

MAX3262 1Gbps, High-Speed Limiting Amplifier
19-0324; Rev 2; 12/97
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
____________________________Features
♦ 900MHz Bandwidth
The MAX3262 has complementary loss-of-signal outputs for interfacing with open-fiber-control (OFC) circuitry. These outputs can be programmed to assert
with input levels between 9mVp-p and 48mVp-p. LOS
hysteresis for any programmed level is nominally
3.0dB, preserving a balance between noise immunity
and dynamic range.
♦ Single +5V Power Supply
♦ 48dB Maximum Gain
♦ Chatter-Free LOS
♦ Programmable LOS Threshold
♦ Fully Differential Architecture
_______________Ordering Information
________________________Applications
1062Mbps Fibre Channel
PART
TEMP. RANGE
MAX3262CAG
0°C to +70°C (TA)
PIN-PACKAGE
24 SSOP
MAX3262C/D
0°C to +100°C (TJ)
Dice*
*Dice are designed to operate over this range but are tested and
guaranteed only at TA = +25°C.
622Mbps SONET
Pin Configuration appears at end of data sheet.
____________________________________________________Typical Operating Circuit
CAZ
CZP
CZN
FILTER
DIN+
CIN
MAX3260
INPUT
DINVCC
DOUT+
RECEIVER WITH
PECL TERMINATIONS
DOUT-
(50Ω TO VCC - 2V)
OUTPUT
MAX3262
CIN
GND
ENB
LOS
VCC
LOSB
50Ω
+5V
+5V
GND
DIV2
VLOS
C1
0.01µF
VCCA
VCCB
VCCC
VCCD
VCCE
+5V
R
4.7k
R
4.7k
LOS
LOSB
+5V
C1
0.01µF
+5V
R1
R2
________________________________________________________________ Maxim Integrated Products
1
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For small orders, phone 408-737-7600 ext. 3468.
MAX3262
________________General Description
The MAX3262 limiting amplifier with its high gain and
wide bandwidth is ideal for use as a post amplifier in
fiber-optic receivers with data rates up to 1Gbps. The
amplifier’s gain can be adjusted between 33dB and
48dB. At maximum gain, signals as small as 6mVp-p
can be amplified to drive devices with PECL inputs.
MAX3262
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
ABSOLUTE MAXIMUM RATINGS
Power Supply, VCC - VEE ......................................................6.0V
Input Voltage, DIN+, DIN- .....................................................6.0V
CZN, CZP, ENB, VLOS, DIV2, LOS+, LOS-.....-0.3V, VCC + 0.3V
DOUT+, DOUT- (with 50Ω load) .......................2.5V, VCC + 0.3V
Continuous Power Dissipation (TA = +70°C)
SSOP (derate 10mW/°C above +70°C) ....................500mW°C
Junction Operating Temperature ......................-55°C to +150°C
Storage Temperature Range .............................-55°C to +175°C
Processing Temperature (Die).........................................+400°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(VCC = +5V, RLOAD = 50Ω to VCC - 2V (equivalent), TA = 0°C to +70°C. Typical values are at VCC = 5V and TA = +25°C.)
PARAMETER
SYMBOL
Power-Supply Current
IVCC
Enable Input Current
IENB
VLOS Input Current
ILOS
CONDITIONS
MIN
TYP
No output load
UNITS
60
mA
150
µA
120
Common-Mode Output Voltage
VCC = 5.0V
LOS+, LOS- Output Low
Voltage
IOUT = -1.0mA
DIV2 Short-Circuit Current
DIV2 = 0V
3.5
3.7
µA
3.8
V
0.5
V
0.5
Differential Output Offset,
DOUT+ to DOUTInput Bias Voltage
MAX
VDIN
2.5
mA
±35
mV
3.0
V
MAX
UNITS
AC ELECTRICAL CHARACTERISTICS
(VCC = +5V, RLOAD = 50Ω to 3V, AC parameters are not tested, TA = +25°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
Power-Supply Rejection Ratio
PSRR
Input referred, 55MHz
LOS Release Time,
Minimum Input
tOFFL
(Note 1)
LOS Release Time,
Maximum Input
tOFFH
(Note 2)
LOS Assert Time
tONL
(Note 1)
Input Voltage Range
VID
Peak-to-peak
LOS Sensitivity Range
VSR
Differential inputs,
peak-to-peak
LOS Hysteresis
HYS
VLOS = 5V, Pattern 27 - 1PRBS
Differential Input Noise
Vn
Pulse-Width Distortion
PWD
Output Edge Speed
tR, tF
Output Voltage Amplitude
VOUT
Small-Signal Bandwidth
BW
MIN
TYP
35
0.020
0.2
0.5
µs
0.5
µs
0.5
µs
0.006
1.8
V
MAX3262C/D
9
48
MAX3262CAG
10
48
1.5
VLOS = 5V, DIV2 = GND (Note 3)
3.0
5.0
80
1Gbps, 8mVp-p input
VOH - VOL
400
600
MAX3262C/D
800
925
MAX3262CAG
750
810
Note 1: Input is a 200MHz square wave, tR < 300ps, 8mVp-p.
Note 2: Input is a 200MHz square wave, tR < 300ps, 1.8Vp-p.
Note 3: Input-referred noise = RMS output noise/low-frequency gain.
2
dB
_______________________________________________________________________________________
mV
dB
µV
40
ps
250
ps
730
mV
MHz
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
VCC SUPPLY CURRENT
(NO OUTPUT LOAD) vs. TEMPERATURE
45
4.75V
4
3
1
4.5
20
40
60
80
100
400
120
800
1000
FREQUENCY (Mbps)
FREQUENCY RESPONSE
55
VLOS = 5V
DIV2 = GND
49
GAIN (dB)
3.0
2.0
VLOS = 5V
DIV2 OPEN
43
VLOS = 3.4V
DIV2 OPEN
37
VLOS = 3.0V
DIV2 OPEN
31
1.0
25
0
0
3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
200
400
600
800 1000 1200 1400
VLOS (V)
FREQUENCY (MHz)
EYE DIAGRAM
LOS OPERATION
1Gbps
RLOAD = 50Ω to VCC - 2V (EQUIVALENT)
VIN = 250mV, VCC = +5V, DIV2 = GND, VLOS = VCC
MAX3262-07
+500mV
600
TEMPERATURE (°C)
MAX3262-04
1Gbps
DIV2 = 0
1,0 PATTERN
PRBS 27-1
4.0
0
LOS HYSTERESIS vs. VLOS
5.0
4.0
5.5
5.0
10 20 30 40 50 60 70 80 90 100
TEMPERATURE (°C)
HYSTERESIS (dB)
0
1-0 PATTERN
6.0
2
0
40
6.5
MAX3262-05
5.0V
5
K28.5 SEQUENCE
(FIBRE CHANNEL IDLE PATTERN)
7.0
MAX3262-06
50
7.5
SENSITIVITY (mVp-p)
HYSTERESIS (dB)
5.25V
55
MAX3262-03
7
6
60
8.0
MAX3262-02
1Gbps WITH 1,0 PATTERN
65
SUPPLY CURRENT (mA)
LOS SENSITIVITY
vs. FREQUENCY
8
MAX3262-01
70
LOS HYSTERESIS
vs. TEMPERATURE
LOS
OUTPUT
100mV/div
DATA
INPUT
VLOS = VCC
-500mV
225ps/div
2µs/div
_______________________________________________________________________________________
3
MAX3262
__________________________________________Typical Operating Characteristics
(VCC = 5V, TA = +25°C, unless otherwise noted.)
MAX3262
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
_______________________________________________________________Pin Description
4
PIN
NAME
FUNCTION
1
VCCB
Positive supply for internal gain stages
2
VLOS
Power detect/LOS level set. Use this input to program the required threshold level for LOS assertion.
3
CZP
Offset-correction loop compensation capacitor. This pin should be connected to the CZN pin through a
100nF to 330nF capacitor, which provides the dominant pole for the offset-correction loop.
4
CZN
Offset-correction loop compensation capacitor. This pin should be connected to the CZP pin through a
100nF to 330nF capacitor, which provides the dominant pole for the offset-correction loop.
5
VCCA
Power supply for the input stage amplifier
6
DIN+
Data Input
7
DIN-
Inverting Data Input
8
GND
Ground for the input stage amplifier
9
ENB
Output Enable. Output gain stage is disabled and LOS circuitry remains functional.
10
DIV2
Input stage gain adjust. Grounding this pin forces the input stage gain to maximum (11dB) for applications
where the LOS threshold level will be set for input signals in the 9mVp-p to 20mVp-p range. Leaving this pin
open forces the gain of the input stage to be divided by two (6dB) for applications where the LOS threshold
level will be set for input signal levels in the 15mVp-p to 48mVp-p range.
11
VTH
Comparator threshold voltage for test only. Leave unconnected.
12
VCCE
Positive supply for the power detect/LOS circuitry
13
GND
Ground for the power detect/LOS circuitry
14
GND
Ground for the LOS+/LOS- buffer circuitry
15
VCCD
Positive supply for the LOS+/LOS- buffer circuitry
16
LOS-
Loss-of-Signal detect. This pin is asserted low when input power drops below the LOS threshold level.
17
LOS+
Loss-of-Signal detect. This pin is asserted high when input power drops below the LOS threshold level.
18
DOUT-
Inverting Data Output
19
DOUT+
Data Output
20
GND
Substrate Ground
21
VCCC
Positive supply for bias generators
22
GND
Ground for bias generators
23
VCC
Positive supply for output buffers
24
GND
Ground for internal gain stages
_______________________________________________________________________________________
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
MAX3262
CAZ
VLOS
OFFSET
CORRECTION
20k
20k
DIN+
DOUT+
5dB/11dB
0dB to 11dB
10dB
10dB
6dB
DIN-
DOUTRMS
DETECT
DIV2
MAX3262
BIAS
ENB
LOS+
REFERENCE
LOS-
Figure 1. Functional Diagram
_______________ Detailed Description
The MAX3262 is an integrated limiting amplifier intended for high-frequency fiber-optic applications. The circuit connects to typical transimpedance amplifiers
found within a fiber-optic link. The linear signal output
from a transimpedance amplifier can contain significant
amounts of noise, and may vary in amplitude over time.
The MAX3262 limiting amplifier quantizes the signal,
and outputs a voltage-limited waveform over a 48dB
input dynamic range.
The MAX3262 provides an offset correction function
that effectively reduces the offset voltage to negligible
levels. In communications systems using NRZ data with
a 50% duty cycle, pulse-width distortion present in the
signal or generated by the transimpedance amplifier
appears as input offset and is partially removed by the
offset correction function. An external capacitor is
required between CZP and CZN to compensate the offset correction loop, determining the lower 3dB point.
Loss-of-Signal Function
The MAX3262 incorporates a chatter-free loss-of-signal
function, which is used to detect that the input signal
has dropped below the level necessary for acceptable
bit error rate performance, or to indicate an open-fiber
condition. The loss-of-signal function is implemented
with a rectifying peak detector, which samples the signal entering the output stage. The output from the peak
detector is compared against an internally generated
threshold, and is used to assert the LOS+ and LOSoutputs.
The loss-of-signal threshold is adjusted by varying the
amplifier gain. The MAX3262 is configurable for gains
between 33dB and 48dB, allowing LOS thresholds
between 9mVp-p and 48mVp-p. Figure 2 shows the
LOS threshold as a function of the DIV2 and VLOS pins.
The DIV2 pin provides a coarse adjustment of 6dB of
gain, while the VLOS pin provides a fine gain adjustment between 0dB and 11dB.
_______________________________________________________________________________________
5
MAX3262
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
VCC = 5V
45
MAX3262-07
LOS ASSERT LEVEL
50
+5V
SENSITIVITY (mVp-p)
40
35
30
RLOS
MAX3262
DIV2 OPEN
LOS+
LOS OUTPUT WITH
DESIRED RISE TIME
25
CLOS
20
LOS
BUFFER
15
10
5
DIV2 GROUNDED
0
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
VLOS (V)
RLOS ≥ 3.3kΩ
Figure 2. MAX3262 Sensitivity vs. VLOS Setting
Figure 3. Setting the LOS Time Constant
Level-detect hysteresis and a 200ns internal delay
ensure chatter-free LOS outputs when the input signal
level is close to the LOS threshold. The hysteresis for
any programmed loss-of-signal level is nominally 2.5dB.
The LOS+ and LOS- outputs are open-collector,
Schottky-clamped transistors, that require pull-up resistors for proper operation (Figure 3). The loss-of-signal
time constant is set externally with the appropriate pull-up
resistor and shunt load capacitance.
The ENB pin allows the user to disable the output signal without removing the input signal.
CIN should be large enough to not affect the signal
quality, but small enough to not affect the LOS assert
time. When an open-fiber condition occurs, the input
coupling capacitors must discharge below the LOS
threshold level before the LOS can assert. The worstcase discharge time would occur with the maximum
input signal and the minimum LOS threshold. In this
case, the input capacitor must discharge from 0.9V to
4.5mV. The time required for this to occur is:
t = (1500)(CIN) In(VMAX / VTHRESH) seconds
Example: If the MAX3262 is configured for 6mV sensitivity, CIN = 100pF results in a lower -3dB frequency of
1MHz, and a maximum LOS delay of about 1µs.
Wire Bonding Die
For reliable operation, the MAX3262 has gold metalization. Connections to the die should be made with gold
wire only, using ball bonding techniques. Wedge bonding is not recommended. Bond pad size is 4 mils.
__________________ Design Procedure
Determining Capacitor Values
The MAX3262 inputs must be AC coupled to allow proper operation of the offset correction function. Figure 4
shows the circuit’s input stage. The circuit’s lower -3dB
point is determined by the input coupling capacitors. The
lower -3dB frequency is 1 / [(2π)(1500Ω)(CIN)] Hz.
6
The offset correction capacitor (CAZ) must be greater
than 100nF to ensure stable operation. This capacitor is
in series with an internal 40kΩ of resistance. The -3dB
point of the offset zeroing circuit is:
1 / [(2π)(CAZ)(40kΩ)] Hz
For CAZ = 180nF, the bandwidth of the offset correction
circuit is 22Hz. Maxim’s proprietary offset-correction
architecture decouples the input coupling time constant
from the offset correction time constant. This ensures
there is no interaction between these two networks, eliminating an additional source of chatter on LOS.
_______________________________________________________________________________________
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
VCC
MAX3262
Layout and PC Board Design
Since the MAX3262 is a high-frequency component,
the circuit’s performance can largely be determined by
board layout and design. A common problem with
high-gain amplifiers is feedback from the large swing
outputs to the input via the power supply. Some fiberoptic limiting amplifiers suffer from LOS “chatter.” The
act of switching the LOS outputs on or off generates
noise on the power supply, which can cause the LOS
outputs to chatter. With proper board layout, the
MAX3262 ensures chatter-free LOS operation.
CIN
DIN+
VIN
CIN
DIN-
1.5k
1.5k
The MAX3262 has five ground pins and a substrate
connection. All of these should be connected to the circuit board’s ground. Use multiple PCB vias close to the
part to connect the grounds. Avoid long, inductive runs,
which can degrade MAX3262 performance. The
MAX3262’s six VCC supply pins must all be connected.
VCCA–VCCE can be collectively decoupled with one
capacitor. VCC (pin 23) should be decoupled separately (see the Typical Operating Circuit).
Figure 4. MAX3262 Equivalent Input Circuit
+5V
82Ω
DOUT+
DOUT+
330Ω
50Ω
MAX3262
120Ω
MAX3262
+5V
ZLOAD
>500Ω
82Ω
DOUT-
DOUT330Ω
a) DRIVING A 50Ω LOAD TO GROUND
50Ω
120Ω
b) DRIVING A HIGH-IMPEDANCE LOAD
Figure 5. Output Termination Techniques
_______________________________________________________________________________________
7
MAX3262
Output Termination
The MAX3262 outputs must be terminated with a 50Ω
load to (VCC - 2V), or a Thevenin equivalent. Figure 5
shows two possible output termination methods.
MAX3262
1Gbps, High-Speed Limiting Amplifier with
Chatter-Free Loss-of-Signal Detection
___________________Pin Configuration
____________________Chip Topography
TOP VIEW
VCCB 1
24 GND
VLOS 2
23 VCC
CZP 3
22 GND
CZN 4
VCCA 5
21 VCCC
MAX3262
V CC C
GND
DOUTLOSDOUT+
LOS+
GND
V CC D
V CC
GND
20 GND
DIN+ 6
19 DOUT+
DIN- 7
18 DOUT-
GND 8
17 LOS+
ENB 9
16 LOS-
DIV2 10
15 VCCD
VTH 11
14 GND
VCCE 12
13 GND
SSOP
0.080"
(2.032mm)
GND
GND
V CC B
V CC E
V LOS
VTH
CZP
DIV2
CZN
V CC A DIN+ DIN- GND
ENB
0.060"
(1.524mm)
TRANSISTOR COUNT: 200
SUBSTRATE CONNECTED TO GND PIN 17
Maxim makes no warranty, representation, or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any liability arising out of the application or use of any product or circuit, and Maxim specifically disclaims any and all liability including, without limitation, consequential or incidental damages. “Typical’’ parameters can and do vary in different applications. All operating parameters, including “typicals”, must be
validated for each customer application by customer’s technical experts. Maxim products are not designed, intended, or authorized for use as components
in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Maxim product could create a situation where personal injury or death may occur.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1997 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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