Si483X-B/Si4820/24 ANTENNA, SCHEMATIC, LAYOUT

Si483X-B/Si4820/24 ANTENNA, SCHEMATIC, LAYOUT
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S i483 X -B/Si4820/24 A NTENNA , S CHEMATIC , L AYOUT ,
AND D E S I G N G UIDEL INES
1. Introduction
This document provides general Si483x-B/Si4820/24 design and AM/FM/SW antenna selection guidelines,
including schematic, BOM and PCB layout. All users should follow the Si483x-B/Si4820/24 design guidelines
presented in Section 2 and Section 3 and choose the appropriate antennas based on the applications and device
used according to Sections 4 through 8.
Wheel-tuned AM/FM Receiver
†
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Si4835-B30
Wheel-tuned AM/FM/SW Receiver
†
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Si4835-B31
Wheel-tuned AM/FM/SW Receiver,
Enhanced SW Tuning Feel
†
†
Si4820-A10
Entry Level Wheel-tuned AM/FM
Receiver, Mono Audio
†
†
Si4824-A10
Entry Level Wheel-tuned AM/FM/SW
Receiver, Mono Audio
†
†
Rev. 0.2 11/11
Whip
Air Loop
AM Antenna
Ferrite Loop
Whip
Headphone
FM Antenna
Si4831-B30
SW Receiver
AM Receiver
FM Receiver
Function
†General Description
FM Receiver
†Part
Number
SW Antenna
Table 1. Part Selection Guide
†
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Copyright © 2011 by Silicon Laboratories
†
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2. Frequency Band Definition and Selection
Five FM bands and five AM bands are defined for the Si4831-B/Si4820. The Si4835-B/Si4824 has 16 SW bands
available. In each FM band, the parts also offer two de-emphasis selections and two LED stereo separation
threshold selections, which result in a total of 41 combinations. This section shows the detailed band definition and
selection information.
2.1. Band Definition
For the Si483x-B/Si4820/24, the FM band definition is a combination of frequency range, de-emphasis and LED
stereo separation threshold. Customers should choose the band according to not only frequency range, but also
de-emphasis setting and LED stereo separation requirements. For AM and SW, simply choose the band according
to the frequency range desired.
Table 2. Band Sequence Definition
Band
Number
2
Band Name Band Frequency
Range
De-emphasis
Stereo LED on
Threshold
(Only for Si483x-B)
Total R to GND
(k, 1%)
Band1
FM1
87–108 MHz
50 µs
Separation = 6 dB,
RSSI = 20
47
Band2
FM1
87–108 MHz
50 µs
Separation = 12 dB,
RSSI = 28
57
Band3
FM1
87–108 MHz
75 µs
Separation = 6 dB,
RSSI = 20
67
Band4
FM1
87–108 MHz
75 µs
Separation = 12 dB,
RSSI = 28
77
Band5
FM2
86.5–109 MHz
50 µs
Separation = 6 dB,
RSSI = 20
87
Band6
FM2
86.5–109 MHz
50 µs
Separation = 12 dB,
RSSI = 28
97
Band7
FM2
86.5–109 MHz
75 µs
Separation = 6 dB,
RSSI = 20
107
Band8
FM2
86.5–109 MHz
75 µs
Separation = 12 dB,
RSSI = 28
117
Band9
FM3
87.3–108.25 MHz
50 µs
Separation = 6 dB,
RSSI = 20
127
Band10
FM3
87.3–108.25 MHz
50 µs
Separation = 12 dB,
RSSI = 28
137
Band11
FM3
87.3–108.25 MHz
75 µs
Separation = 6 dB,
RSSI = 20
147
Band12
FM3
87.3–108.25 MHz
75 µs
Separation = 12 dB,
RSSI = 28
157
Band13
FM4
76–90 MHz
50 µs
Separation = 6 dB,
RSSI = 20
167
Band14
FM4
76–90 MHz
50 µs
Separation = 12 dB,
RSSI = 28
177
Rev. 0.2
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Table 2. Band Sequence Definition (Continued)
Band
Number
Band Name Band Frequency
Range
De-emphasis
Stereo LED on
Threshold
(Only for Si483x-B)
Total R to GND
(k, 1%)
Band15
FM4
76–90 MHz
75 µs
Separation = 6 dB,
RSSI = 20
187
Band16
FM4
76–90 MHz
75 µs
Separation = 12 dB,
RSSI = 28
197
Band17
FM5
64–87 MHz
50 µs
Separation = 6 dB,
RSSI = 20
207
Band18
FM5
64–87 MHz
50 µs
Separation = 12 dB,
RSSI = 28
217
Band19
FM5
64–87 MHz
75 µs
Separation = 6 dB,
RSSI = 20
227
Band20
FM5
64–87 MHz
75 µs
Separation = 12 dB,
RSSI = 28
237
Band21
AM1
520–1710 kHz
247
Band22
AM2
522–1620 kHz
257
Band23
AM3
504–1665 kHz
267
Band24
AM4
520–1730 kHz
277
Band25
AM5
510–1750 kHz
287
Band26
SW1
5.6–6.4 MHz
297
Band27
SW2
5.95–6.2 MHz
307
Band28
SW3
6.8–7.6 MHz
317
Band29
SW4
7.1–7.6 MHz
327
Band30
SW5
9.2–10 MHz
337
Band31
SW6
9.2–9.9 MHz
347
Band32
SW7
11.45–12.25 MHz
357
Band33
SW8
11.6–12.2 MHz
367
Band34
SW9
13.4–14.2 MHz
377
Band35
SW10
13.57–13.87 MHz
387
Band36
SW11
15–15.9 MHz
397
Band37
SW12
15.1–15.8 MHz
407
Band38
SW13
17.1–18 MHz
417
Band39
SW14
17.48–17.9 MHz
427
Band40
SW15
21.2–22 MHz
437
Band41
SW16
21.45–21.85 MHz
447
Rev. 0.2
3
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2.2. Si483x-B/Si4820/24 Band Selection
Refer to Figure 1 below for the band selection circuits. Selecting a band determines the resistance value from the
band select pin to GND.
To select a specific band, you need to ensure two things:
1. Total value of resistance from the BAND to GND is equal to the value specified in Table 2
2. Total resistance from TUNE1 to GND is 500 k in 1% tolerance
The following sections describe some commonly used bands and their respective selection circuits.
2.2.1. Typical 12-band application
Figure 1 and Table 3 illustrate the band and resistor value details for a typical 12-band application.
4
Rev. 0.2
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TUNE1
R36
33k 1%
R43
30k 1%
SW15 (21.2MHz - 22MHz)
R35
20k 1%
SW13 (17.1MHz - 18MHz)
R15
20k 1%
SW11 (15MHz - 15.9MHz)
Si4835/24 only
R10
20k 1%
SW9 (13.4MHz - 14.2MHz)
R12
20k 1%
S2
BAND
1
SW7(11.45MHz - 12.25MHz)
2
3
4
5
6
7
8
9
10
11
12
13
R11
20k 1%
SW5(9.2MHz - 10.0MHz)
R14
20k 1%
SW3(6.8MHz - 7.6MHz)
R9
20k 1%
SW1 (5.6MHz - 6.4MHz)
R8
50k 1%
AM1 (520kHz - 1710kHz)
R7
20k 1%
FM5 (64MHz - 87MHz)
R28
40k 1%
FM4 (76MHz - 90MHz)
R29
120k 1%
FM1 (87MHz - 108MHz)
R33
20k 1%
R44
47k 1%
Figure 1. Typical 12-Band Selection Circuit
Rev. 0.2
5
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Table 3. Typical 12-Band Selection
6
Band
Number
Band
Name
Band Frequency
Range
De-emphasis
Stereo LED on
Threshold
(Only for Si483x-B)
Total R to GND
(k, 1%)
Band3
FM1
87–108 MHz
75 µs
Separation = 6 dB,
RSSI = 20
67
Band15
FM4
76–90 MHz
75 µs
Separation = 6 dB,
RSSI = 20
187
Band19
FM5
64–87 MHz
75 µs
Separation = 6 dB,
RSSI = 20
227
Band21
AM1
520–1710 kHz
247
Band26
SW1
5.6–6.4 MHz
297
Band28
SW3
6.8–7.6 MHz
317
Band30
SW5
9.2–10 MHz
337
Band32
SW7
11.45–12.25 MHz
357
Band34
SW9
13.4–14.2 MHz
377
Band36
SW11
15–15.9 MHz
397
Band38
SW13
17.1–18 MHz
417
Band40
SW15
21.2–22 MHz
437
Rev. 0.2
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2.2.2. Typical 2-band Application for Europe
Table 4 and Figure 2 show the band and resistor value details for a typical European 2-band application.
Table 4. Typical European 2-Band Selection
Band
Number
Band
Name
Band Frequency
Range
De-emphasis
Stereo LED on
Threshold
(Only for Si483x-B)
Total R to GND
(k, 1%)
Band2
FM1
87–108 MHz
50 µs
Separation = 12 dB,
RSSI = 28
57
Band22
AM2
522–1620 kHz
257
Figure 2. Typical 2-Band Selection Circuit for Europe
Rev. 0.2
7
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2.2.3. Typical 2-band application for US
Table 5 and Figure 3 show the band and resistor value details for a typical 2-band application for the U.S.
Table 5. Typical U.S. 2-Band Selection
Band
Number
Band
Name
Band Frequency
Range
De-emphasis
Stereo LED on
Threshold
(Only for Si483x-B)
Total R to GND
(k, 1%)
Band4
FM1
87–108 MHz
75 µs
Separation = 12 dB,
RSSI = 28
77
Band21
AM1
520–1710 kHz
247
Figure 3. Typical 2-Band Selection Circuit for US
8
Rev. 0.2
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3. Si483x-B/Si4820/24 SSOP Schematic and Layout
This section shows the typical schematic and layout required for optimal Si483x-B/Si4820/24 performance.
There are basically two working modes for the Si483x-B: “Volume” and “Bass/Treble” modes. Adding a pull-up
resistor of 10 k on pin2 STATION sets the chip in "Volume" mode and removing the pull-up resistor sets the chip in
"Bass/Treble" mode, as illustrated in Figure 4. When working in Bass/Treble mode, the Bass/Treble can be
controlled via two push buttons with eight levels or by a slide switch with two or three levels. When working in
“Volume” mode, tuner audio output volume can be adjusted with 2 push buttons in 32 steps (2 dB per step).
Additionally, the default power up volume level can be set with pull-up/down resistors. Compared with the Si483xB, Si4820/24 only works in “Volume” mode, not “Bass/Treble” mode. The following sections describe in detail the
applications circuits for different working modes.
Figure 4. Si483x-B Mode Selection
Rev. 0.2
9
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3.1. Si483x-B/Si4820/24 Basic Volume Mode Applications Circuits
Figure 5 and Figure 6 illustrate the basic applications circuits for typical 4-band FM/AM radios if using Si4831-B/
Si4820 or 12-band FM/AM/SW radios if using Si4835-B/Si4824. The chip works in "Volume" mode without internal
volume adjustment. Volume control can be performed at audio amplifier circuit stage. For Si483x-B, the pull-up
resistor R42 of 10K for pin 2 STATION is a must for this application.
C6 and C15 are required bypass capacitors for VDD1/VDD2 power supply pin 20/21. Place C6/C15 as close as
possible to the VDD1/VDD2 pin 20/21 and DBYP pin 22. These recommendations are made to reduce the size of
the current loop created by the bypass cap and routing, minimize bypass cap impedance and return all currents to
the DBYP pin.
Pin 22 is the dedicated bypass capacitor pin. Do not connect it to power supply GND on PCB.
Pin 13 and pin 14 are the GND of the chip, these pins must be well connected to the power supply GND on PCB.
Pin 9 is the RFGND of the chip, it must be well connected to the power supply GND on PCB.
When doing PCB layout, try to create a large GND plane underneath and around the chip. Route all GND
(including RFGND) pins to the GND plane.
C4 and/or C7 (4.7uF) are ac coupling caps for receiver analog audio output from pin 23 and/or pin 24. The input
resistance of the amplifier R, such as a headphone amplifier, and the capacitor C will set the high pass pole given
by Equation 1. Placement location is not critical.
1
f c = ---------------2RC
Equation 1.
C2 and C3 (22 pF) are crystal loading caps required only when using the internal oscillator feature. Refer to the
crystal data sheet for the proper load capacitance and be certain to account for parasitic capacitance. Place caps
C2 and C3 such that they share a common GND connection and the current loop area of the crystal and loading
caps is minimized.
Y1 (32.768 kHz) is an optional crystal required only when using the internal oscillator feature. Place the crystal Y1
as close to XTALO pin 18 and XTALI pin 19 as possible to minimize current loops. If applying an external clock
(32.768 kHz) to XTALI, leave XTALO floating.
Do not route digital signals or reference clock traces near pin 6 and 7. Do not route Pin 6 and 7. These pins must
be left floating to guarantee proper operation.
Pin 16, 17 are volume control or bass/treble control pins for using tuner internal volume control function or bass/
treble control function. In this basic application circuit, the tuner internal volume control function is not used, just
connect the two pins to GND.
VR1 (100K / 10%), R27, C1, C13 constitute the tuning circuit. 10 k at 10% tolerance is recommended for VR1.
1P12T switch S2 together with resistor ladder constitute band select circuits. Si4831/Si4820 includes all AM and
FM bands as defined in above section 2.1, Si4835/Si4824 includes all AM, FM and SW bands.
Q1(2SC9018) together with it’s peripherals B6, C30,31,33,36, R31,32,34,41 is the LNA circuit for all SW bands, the
LNA is switched off by LNA_EN signal in AM and FM mode controlled by Si4835/Si4824.
For Si4820/24, do not route pin 23. This pin must be left floating to guarantee proper operation.
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Figure 5. Si483x-B Basic Volume Mode Applications Circuit
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TUNE1 [1]
R36
33k 1%
R43
30k 1%
ANT2
SW8 (21.2MHz - 22MHz)
[1] TUNE1
FM/SW
VR1
50k 10%
C1
47u
0.1u
R35
20k 1%
For Si4824 only
C13
VCC
R27
C36
0.47u
100R
R32
10R
C34
33p
[1] BAND
1
2
NC
TUNE1
LNA_EN
3
5
6
7
8
9
4
TUNE2
BAND
NC
NC
FMI
10
11
S2
BAND [1]
NC
DBYP
VDD2
AOUT
24
23
22
21
VDD1
20
XTALI
19
VOL-
VOL+
RST
XTAL0
18
17
16
14
13
Si482x-A
C4
For Si4824 only
4.7u
VCC
R6
100k
C6
C15
0.1u
4u7
AOUT
1
SW4(11.45MHz - 12.25MHz)
2
3
4
5
6
7
8
9
10
11
12
13
R11
20k 1%
SW3(9.2MHz - 10.0MHz)
R14
20k 1%
SW2(6.8MHz - 7.6MHz)
R9
20k 1%
VCC
C19
0.1u
R12
20k 1%
[1] LNA_EN
RFGND
NC
NC
AMI
SW5 (13.4MHz - 14.2MHz)
U1
GND
R34
100k
Q1
2SC9018
0.47u
15
33n
10p
GND
2.5k/100M
C5
ANT1
MW ferrite antenna
R41
120k
C30
B6
C33
12
270nH
R31
1k
[1]
SW6 (15MHz - 15.9MHz)
R10
20k 1%
L2
C31
33n
LNA_EN
SW7 (17.1MHz - 18MHz)
R15
20k 1%
SW1 (5.6MHz - 6.4MHz)
R8
50k 1%
Y1
AM1 (520kHz - 1710kHz)
R7
32.768KHz
C2
22p
20k 1%
C3
22p
FM3 (64MHz - 87MHz)
R28
40k 1%
optional
FM2 (76MHz - 90MHz)
R29
120k 1%
FM1 (87MHz - 108MHz)
R33
20k 1%
R44
47k 1%
Figure 6. Si4820/24 Basic Volume Mode Applications Circuit
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3.2. Si483x-B Applications Circuits with 9-level Bass/Treble Control via 2 Push Buttons
Figure 7 sets Si483x-B in Bass/Treble mode by removing the pull-up resistor of pin 2 STATION. Pushing button S3
once increases bass effect by one level, and pushing button S4 once increases treble effect by one level. By
pressing and holding one of the buttons, the bass or treble effect will automatically step through all levels until
reaching their maximums. There are nine levels for bass/treble control.
Figure 7. Si483x-B Applications Circuit with 9-Level Bass/Treble Control
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Figure 8. Si483x-B 3-Level Bass/Treble Mode Applications Circuits
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3.3. Si483x-B Applications Circuits with 3-level Bass/Treble Control via Slide Switch
Figure 8 sets Si483x-B in Bass/Treble mode by removing the pull-up resistor of pin 2 STATION. Slide switch S5
controls bass/treble effect in three levels, bass/normal/treble.
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3.4. Si48x-B/Si4820/24 Application Circuits with 32-Level Volume Control via 2 Push
Buttons
Figure 9 sets Si483x-B in "Volume" mode by adding the pull-up resistor R42 of 10K at pin 2 STATION. Figure 10
illustrates the application circuit for Si4820/24. Pressing button S3 once decreases the volume level by 2 dB;
pressing button S4 once increases the volume level by 2 dB. A total of 32 steps (2 dB per step) are available for the
push button volume control. If pressing and holding S3 or S4, tuner volume will step through all levels until
reaching the minimum or maximum, respectively.
Figure 9. Si483x-B Applications Circuits with 32-Level Volume Control
15
9&&
AN555
TUNE1 [1]
R36
33k 1%
R43
30k 1%
ANT2
SW8 (21.2MHz - 22MHz)
[1] TUNE1
FM/SW
VR1
50k 10%
C1
47u
0.1u
For Si4824 only
C13
R35
20k 1%
VCC
R27
C36
0.47u
100R
R32
10R
C34
33p
[1] BAND
1
2
NC
TUNE1
LNA_EN
3
5
6
7
8
9
4
TUNE2
BAND
NC
NC
FMI
10
11
S2
BAND [1]
NC
DBYP
VDD2
AOUT
24
23
22
21
VDD1
20
XTAL0
VOL-
XTALI
19
18
17
VOL+
16
14
13
Si482x-A
C4
For Si4824 only
4.7u
VCC
VCC
VCC
R6
100k
C6
C15
0.1u
4u7
AOUT
1
SW4(11.45MHz - 12.25MHz)
2
3
4
5
6
7
8
9
10
11
12
13
R11
20k 1%
SW3(9.2MHz - 10.0MHz)
R14
20k 1%
SW2(6.8MHz - 7.6MHz)
R9
20k 1%
VCC
C19
0.1u
R12
20k 1%
[1] LNA_EN
RFGND
NC
SW5 (13.4MHz - 14.2MHz)
U1
GND
R34
100k
RST
Q1
2SC9018
NC
AMI
0.47u
15
33n
10p
GND
2.5k/100M
C5
ANT1
MW ferrite antenna
R41
120k
C30
B6
C33
12
270nH
R31
1k
[1]
SW6 (15MHz - 15.9MHz)
R10
20k 1%
L2
C31
33n
LNA_EN
SW7 (17.1MHz - 18MHz)
R15
20k 1%
SW1 (5.6MHz - 6.4MHz)
R8
volume+
S4
volume-
S3
50k 1%
Y1
AM1 (520kHz - 1710kHz)
R7
32.768KHz
C2
22p
20k 1%
C3
22p
FM3 (64MHz - 87MHz)
R28
40k 1%
R37
56k
R38
56k
optional
FM2 (76MHz - 90MHz)
R29
120k 1%
FM1 (87MHz - 108MHz)
R33
20k 1%
R44
47k 1%
Figure 10. Si4820/24 Applications Circuit with 32-Level Volume Control
At the device power up, Si483x-B/Si4820/24 will put the output volume at some default levels according to the push
button configurations as shown in Figure 11. There are four default volume level choices. Adding pull-down
resistors to both pin 16 and 17 sets the default volume to maximum, typically 80 mVrms for FM and 60 mVrms for
AM. Different pin 16 and 17 pull-up/down resistor combinations can set the default volume to either Max, Max-6dB,
Max-12dB or Max-18dB. For example, in Figure 9, two pull-up resistors are connected to pin 16 and pin 17, which
sets the default volume to Max-18dB.
16
Rev. 0.2
AN555
Figure 11. Si483x-B/Si4820/24 Default Volume Selection in Volume Mode
3.5. Application Circuits for Memorization of User Settings
Si483x-B/Si4820/24 has high retention memory (HRM) built-in that can memorize the last volume and bass/treble
settings so that at the next power up, the unit will automatically restore the volume and bass/treble settings before
the last power off. The unit requires pin 20 Vdd1 to be connected to an always-on power source such as battery
terminals.
During power off/on cycling, there is a low probability that the user setting data in HRM can be corrupted by
transient. If the tuner finds that the stored data in HRM is corrupted at power on, it will switch to use the default
volume or bass/treble setting. To safeguard the integrity of HRM data, users are advised to ensure that the Reset
pin (RSTB) voltage goes down to 0.3*VDD before the VDD2 voltage drops to 1.65 V during the power off process.
A 2P2T, power on/off switch S3 in Figure 12 is recommended, with one pole of S3 short pin15 RSTB to GND
immediately at the power off event.
Applying always-on power supply voltage to Vdd1 and using 2P2T power on/off switch to connect RSTB will also
improve the tuned channel consistency before power off and after power on. Si483x-B/Si4820/24 memorizes the
last tuned station before power off and restores the original tuned station at power up after confirming that there is
not a large enough position change on PVR during the power off/on cycle.
Rev. 0.2
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AN555
Figure 12. Si483x-B Applications Circuits with User Setting Memory
YROXPH
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6
AN555
3.6. Si483x-B/Si4820/24 Bill of Materials
3.6.1. Si483x-B/Si4820/24 Basic Volume Mode Applications Circuit BOM
Table 6. Si483x-B Basic Volume Mode Applications Circuit BOM
Component(s)
Value/Description
Supplier
C4,C7,C15
Capacitor 4.7 µF, ±20%, Z5U/X7R
Murata
C13
Capacitor 47 µF, ±20%, Z5U/X7R
Murata
C1,C6,C19
Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R
Murata
C36
Supply bypass capacitor, 0.47 µF, ±20%, Z5U/X7R
Murata
C34
RF coupling capacitors, 33 pF, ±5%, COG
Murata
L2
Inductor 270 nH.
Murata
R5,R21
LED biasing resistors, 200 , ±5%
Venkel
VR1
Variable resistor (POT), 100 k, , ±10% 
Kennon
D1,D3
Station and Stereo indicating LEDs
Any, depends on
customer
U1
Si483xB AM/FM/SW Analog Tune Analog Display Radio Tuner
Silicon Laboratories
R6
Resistor, 100 k, ±5%
Venkel
R27
Resistor, 100 ,, ±5%
Venkel
R28
Band switching resistor, 40 k,, ±1%
Venkel
R44
Band switching resistor, 47 k,, ±1%
Venkel
R36
Band switching resistor, 33 k,, ±1%
Venkel
R43
Band switching resistor, 30 k,, ±1%
Venkel
R7,R33
Band switching resistor, 20 k,, ±1%
Venkel
R29
Band switching resistor, 120 k,, ±1%
Venkel
S2
Band switch
Shengda
C2, C3
Crystal load capacitors, 22 pF, ±5%, COG
(Optional: for crystal oscillator option)
Venkel
Y1
32.768 kHz crystal (Optional: for crystal oscillator option)
Epson
ANT2
Whip antenna
Various
ANT1
MW ferrite antenna 220 µH
Jiaxin Electronics
Rev. 0.2
19
AN555
Table 7. Si4820/24 Basic Volume Mode Applications Circuit BOM
Component(s)
Supplier
C4,C7,C15
Capacitor 4.7 µF, ±20%, Z5U/X7R
Murata
C13
Capacitor 4.7 µF, ±20%, Z5U/X7R
Murata
C1,C6,C19
Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R
Murata
C36
Supply bypass capacitor, 0.47 µF, ±20%, Z5U/X7R
Murata
C34
RF coupling capacitors, 33 pF, ±5%, COG
Murata
Inductor 270 nH
Murata
Variable resistor (POT), 100 k, ±10%
Kennon
L2
VR1
U1
Si4820/24 AM/FM/SW Analog Tune Analog Display Radio Tuner
R6
Resistor, 100 k, ±5%
Venkel
R27
Resistor, 100 , ±5%
Venkel
R28
Band switching resistor, 40 k, ±1%
Venkel
R44
Band switching resistor, 47 k, ±1%
Venkel
R36
Band switching resistor, 33 k, ±1%
Venkel
R43
Band switching resistor, 30 k, ±1%
Venkel
R7,R33
Band switching resistor, 20 k, ±1%
Venkel
R29
Band switching resistor, 120 k, ±1%
Venkel
S2
C2, C3
Band switch
Silicon Laboratories
Shengda
Crystal load capacitors, 22 pF, ±5%, COG
(Optional: for crystal oscillator option)
Venkel
32.768 kHz crystal (Optional: for crystal oscillator option)
Epson
ANT2
Whip antenna
Various
ANT1
MW ferrite antenna 220 µH.
Y1
20
Value/Description
Jiaxin Electronics
Rev. 0.2
AN555
Table 8. Si4835-B/Si4824 Additional BOM (for 8 SW Bands)
Component(s)
Value/Description
Supplier
C36
Capacitor, 0.47 µF, ±20%, Z5U/X7R
Murata
C33
Capacitor capacitors, 10 pF, ±5%, COG
Murata
C30-31
Capacitor capacitors, 33 nF, ±5%, COG
Murata
B6
Ferrite bead,2.5k, 100 MHz
Murata
Q1
RF transistor, 2SC9018.
ETC
R34
Resistor, 100 k, ±5%
Venkel
R41
Resistor, 120 k, ±5%
Venkel
R32
Resistor, 10R, ±5%
Venkel
R31
Resistor, 1k,, ±5%
Venkel
R9-12,R14-15,R35
Band switching resistor, 20 k,, ±1%
Venkel
R8
Band switching resistor, 50 k, ±1%
Venkel
3.6.2. Additional BOM for Applications Circuit with 9-level Bass/Treble Control via Push Buttons
Table 9. Si483x-B Additional BOM for 9-Level Bass/Treble Control
Component(s)
Value/Description
Supplier
R1-2
Resistor, 56 k, ±5%
Venkel
S3-4
Button switch
Various
3.6.3. Additional BOM for Application Circuit with 3-level Bass/Treble Control via Slide Switch
Table 10. Si483x-B Additional BOM for 3-Level Bass/Treble Control
Component(s)
Value/Description
Supplier
R37-38
Resistor, 56 k, ±5%
Venkel
S5
Slide switch
Shengda
3.6.4. Additional BOM for Application Circuit with 32-level Volume Control via Push Buttons
Table 11. Si483x-B Additional BOM for 32-Level Volume Control
Component(s)
Value/Description
Supplier
R1-2
Resistor, 56 k, ±5%
Venkel
S3-4
Button switch
Various
Rev. 0.2
21
AN555
Table 12. Si4820/24 Addtional BOM for 32-Level Volume Control
Component(s)
Value/Description
Supplier
R37-38
Resistor, 56 k, ±5%
Venkel
S3-4
Button switch
Various
3.6.5. Additional BOM for Application Circuit with Memorization of User Settings
Table 13. Si483x-B Additional BOM for User Setting Memory
22
Component(s)
Value/Description
Component(s)
R1-2
Resistor, 56 k, ±5%
Venkel
S3-4
Button switch
Various
S1
2P2T slide switch
Shengda
R16
Resistor, 200R, ±5%
Venkel
C40
Supply bypass electrolytic capacitor, 100 µF, 4 V
Any
C39
Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R
Murata
Rev. 0.2
AN555
3.7. Si483x-B/Si4820/24 PCB Layout Guidelines
1-layer
PCB is used for Si483x-B/Si4820/24
routed by large plane
Power routed with traces
0402 component size or larger
10 mil traces width
20 mil trace spacing
15 mil component spacing
Recommended to keep the AM ferrite loop antenna at least 5 cm away from the tuner chip
Keep the AM ferrite loop antenna at least 5 cm away from MCU, audio AMP, and other circuits which have
AM interference
Place Vdd1/Vdd2 bypass capacitor C6, C15 as close as possible to the supply (pin 20/pin 21) and DBYP (pin 22).
GND
Do not connect the DBYP (pin 22) to the board GND.
Place the crystal as close to XTALO (pin 18) and XTALI (pin 19) as possible.
Route all GND (including RFGND) pins to the GND plane underneath the chip. Try to create a large GND plane
underneath and around the chip.
Do not route pin 6 and 7. These pins must be left floating to guarantee proper operation.
Keep the Tune1 and Tune2 traces away from pin 6 and pin 7. Route Tune1 and Tune2 traces in parallel and the
same way.
Place C1, C13 as close to pin3 TUNE1 as possible.
For Si4820/24, do not route pin 23, leave it floating to guarantee proper operation.
Copy the Si483x-B layout example as much as possible when doing PCB layout.
Figure 13. Si483x-B PCB Layout Example
Rev. 0.2
23
AN555
4. Headphone Antenna for FM Receive
The Si483x-B/Si4820/24 FM Receiver component supports a headphone antenna interface through the FMI pin. A
headphone antenna with a length between 1.1 and 1.45 m suits the FM application very well because it is
approximately half the FM wavelength (FM wavelength is ~3 m).
4.1. Headphone Antenna Design
A typical headphone cable will contain three or more conductors. The left and right audio channels are driven by a
headphone amplifier onto left and right audio conductors and the common audio conductor is used for the audio
return path and FM antenna. Additional conductors may be used for microphone audio, switching, or other
functions, and in some applications the FM antenna will be a separate conductor within the cable. A representation
of a typical application is shown in Figure 14.
Figure 14. Typical Headphone Antenna Application
24
Rev. 0.2
AN555
4.2. Headphone Antenna Schematic
Figure 15. Headphone Antenna Schematic
The headphone antenna implementation requires components LMATCH, C4, F1, and F2 for a minimal
implementation. The ESD protection diodes and headphone amplifier components are system components that will
be required for proper implementation of any tuner.
Inductor LMATCH is selected to maximize the voltage gain across the FM band. LMATCH should be selected with
a Q of 15 or greater at 100 MHz and minimal dc resistance.
AC-coupling capacitor C4 is used to remove a dc offset on the FMI input. This capacitor must be chosen to be large
enough to cause negligible loss with an LNA input capacitance of 4 to 6 pF. The recommended value is 100 pF to
1 nF.
Ferrite beads F1 and F2 provide a low-impedance audio path and high-impedance RF path between the
headphone amplifier and the headphone. Ferrite beads should be placed on each antenna conductor connected to
nodes other than the FMIP such as left and right audio, microphone audio, switching, etc. In the example shown in
Figure 15, these nodes are the left and right audio conductors. Ferrite beads should be 2.5 k or greater at
100 MHz, such as the Murata BLM18BD252SN1. High resistance at 100 MHz is desirable to maximize RSHUNT,
and therefore, RP. Refer to “AN383: Si47xx Antenna, Schematic, Layout, and Design Guidelines,” Appendix A–FM
Receive Headphone Antenna Interface Model for a complete description of RSHUNT, RP, etc.
ESD diodes D1, D2, and D3 are recommended if design requirements exceed the ESD rating of the headphone
amplifier and the Si483x-B/Si4820/24. Diodes should be chosen with no more than 1 pF parasitic capacitance,
such as the California Micro Devices CM1210. Diode capacitance should be minimized to reduce CSHUNT and,
therefore, CP. If D1 and D2 must be chosen with a capacitance greater than 1 pF, they should be placed between
the ferrite beads F1 and F2 and the headphone amplifier to minimize CSHUNT. This placement will, however,
reduce the effectiveness of the ESD protection devices. Diode D3 may not be relocated and must therefore have a
capacitance less than 1 pF. Note that each diode package contains two devices to protect against positive and
negative polarity ESD events.
C9 and C10 are 125 uF ac coupling capacitors required when the audio amplifier does not have a common mode
output voltage and the audio output is swinging above and below ground.
Optional bleed resistors R5 and R6 may be desirable to discharge the ac-coupling capacitors when the headphone
cable is removed.
Rev. 0.2
25
AN555
Optional RF shunt capacitors C5 and C6 may be placed on the left and right audio traces at the headphone
amplifier output to reduce the level of digital noise passed to the antenna. The recommended value is 100 pF or
greater, however, the designer should confirm that the headphone amplifier is capable of driving the selected shunt
capacitance.
The schematic example in Figure 15 uses the National Semiconductor LM4910 headphone amplifier. Passive
components R1 R4 and C7 C8 are required for the LM4910 headphone amplifier as described in the LM4910 data
sheet. The gain of the right and left amplifiers is R3/R1 and R4/R2, respectively. These gains can be adjusted by
changing the values of resistors R3 and R4. As a general guide, gain between 0.6 and 1.0 is recommended for the
headphone amplifier, depending on the gain of the headphone elements. Capacitors C7 and C8 are ac-coupling
capacitors required for the LM4910 interface. These capacitors, in conjunction with resistors R1 and R2, create a
high-pass filter that sets the audio amplifier's lower frequency limit. The high-pass corner frequencies for the right
and left amplifiers are:
1
1
f CRIGHT = -----------------------------------  f CLEFT = ----------------------------------2  R1  C7
2  R2  C8
Equation 2.
With the specified BOM components, the corner frequency of the headphone amplifier is approximately 20 Hz.
Capacitor C1 is the supply bypass capacitor for the audio amplifier. The LM4910 can also be shut down by
applying a logic low voltage to the number 3 pin. The maximum logic low level is 0.4 V and the minimum logic high
level is 1.5 V.
The bill of materials for the typical application schematic shown in Figure 15 is provided in Table 14. Note that
manufacturer is not critical for resistors and capacitors.
4.3. Headphone Antenna Bill of Materials
Table 14. Headphone Antenna Bill of Materials
26
Designator
Description
LMATCH
IND, 0603, SM, 270 nH, MURATA, LQW18ANR27J00D
C4
AC coupling cap, SM, 0402, X7R, 100 pF
D1, D2, D3
IC, SM, ESD DIODE, SOT23-3, California Micro Devices, CM1210-01ST
U3
IC, SM, HEADPHONE AMP, National Semiconductor, LM4910MA
R1, R2, R3, R4
RES, SM, 0603, 20 k
C7, C8
CAP, SM, 0603, 0.39 UF, X7R
C5, C6
CAP, SM, 0402, C0G, 100 pF
R5, R6
RES, SM, 0603, 100 k
F1, F2
FERRITE BEAD, SM, 0603, 2.5 k, Murata, BLM18BD252SN1D
C1
CAP, SM, 0402, X7R, 0.1 µF
R7
RES, SM, 0402, 10 k
Rev. 0.2
AN555
4.4. Headphone Antenna Layout
To minimize inductive and capacitive coupling, inductor LMATCH and headphone jack J24 should be placed
together and as far from noise sources such as clocks and digital circuits as possible. LMATCH should be placed
near the headphone connector to keep audio currents away from the chip.
To minimize CSHUNT and CP, place ferrite beads F1 and F2 as close as possible to the headphone connector.
To maximize ESD protection diode effectiveness, place diodes D1, D2, and D3 as close as possible to the
headphone connector. If capacitance larger than 1 pF is required for D1 and D2, both components should be
placed between FB1, FB2, and the headphone amplifier to minimize CSHUNT.
Place the chip as close as possible to the headphone connector to minimize antenna trace capacitance,
CPCBANT. Keep the trace length short and narrow and as far above the reference plane as possible, restrict the
trace to a microstrip topology (trace routes on the top or bottom PCB layers only), minimize trace vias, and relieve
ground fill on the trace layer. Note that minimizing capacitance has the effect of maximizing characteristic
impedance. It is not necessary to design for 50  transmission lines.
To reduce the level of digital noise passed to the antenna, RF shunt capacitors C5 and C6 may be placed on the
left and right audio traces close to the headphone amplifier audio output pins. The recommended value is 100 pF
or greater; however, the designer should confirm that the headphone amplifier is capable of driving the selected
shunt capacitance.
4.5. Headphone Antenna Design Checklist
Select
an antenna length of 1.1 to 1.45 m.
Select matching inductor LMATCH to maximize signal strength across the FM band.
Select matching inductor LMATCH with a Q of 15 or greater at 100 MHz and minimal dc resistance.
Place inductor LMATCH and headphone connector together and as far from potential noise sources as
possible to reduce capacitive and inductive coupling.
Place the chip close to the headphone connector to minimize antenna trace length. Minimizing trace length
reduces CP and the possibility for inductive and capacitive coupling into the antenna by noise sources.
This recommendation must be followed for optimal device performance.
Select ferrite beads F1-F2 with 2.5 k or greater resistance at 100 MHz to maximize RSHUNT and,
therefore, RP.
Place ferrite beads F1-F2 close to the headphone connector.
Select ESD diodes D1-D3 with minimum capacitance.
Place ESD diodes D1-D3 as close as possible to the headphone connector for maximum effectiveness.
Place optional RF shunt capacitors near the headphone amplifier’s left and right audio output pins to
reduce the level of digital noise passed to the antenna.
Rev. 0.2
27
AN555
5. Whip Antenna for FM Receiver
A whip antenna is a typical monopole antenna.
5.1. FM Whip Antenna Design
A whip antenna is a monopole antenna with a stiff but flexible wire mounted vertically with one end adjacent to the
ground plane.
There are various types of whip antennas including long, non-telescopic metal whip antennas, telescopic metal
whip antennas, and rubber whip antennas. Figure 16 shows the telescopic whip antenna.
Figure 16. Telescopic Whip Antennas
The whip antenna is capacitive, and its output capacitance depends on the length of the antenna (maximum length
~56 cm). At 56 cm length, the capacitance of the whip antenna ranges from 18 to 32 pF for the US FM band. The
antenna capacitance is about 22 pF in the center of the US FM band (98 MHz).
5.2. FM Whip Antenna Schematic
Figure 17. FM Whip Antenna Schematic
L1 (56 nH) is the matching inductor and it combines with the antenna impedance and the FMI impedance to
resonate in the FM band.
C5 (1nF) is the ac coupling cap going to the FMI pin.
U3 is a required ESD diode since the antenna is exposed. The diode should be chosen with no more than 1 pF
parasitic capacitance, such as the California Micro Device CM1213.
28
Rev. 0.2
AN555
5.3. FM Whip Antenna Bill of Materials
Table 15. FM Whip Antenna Bill of Materials
Designator
Description
WIP_ANTENNA
Whip Antenna
L1
Tuning Inductor, 0603, SM, 56 nH, MURATA, LQW18AN56nJ00D
C5
AC coupling capacitor,
1 nF, 10%, COG
U3
IC, SM, ESD DIODE, SOT23-3, California Micro Devices, CM1213-01ST
5.4. FM Whip Antenna Layout
Place the chip as close as possible to the whip antenna. This will minimize the trace length between the device and
whip antenna, which will minimize parasitic capacitance and the possibility of noise coupling. Place inductor L1 and
the antenna connector together and as far from potential noise sources as possible. Place the ac coupling
capacitor, C5, as close to the FMI pin as possible. Place ESD diode U3 as close as possible to the whip antenna
input connector for maximum effectiveness.
5.5. FM Whip Antenna Design Checklist
Maximize
whip antenna length for optimal performance.
Select matching inductor L1 with a Q of 15 or greater at 100 MHz and minimal dc resistance.
Select L1 inductor value to maximize resonance gain from FM frequency (64 MHz) to FM frequency
(109 MHz)
Place L1 and whip antenna close together and as far from potential noise sources as possible to reduce
capacitive and inductive coupling.
Place the chip as close as possible to the whip antenna to minimize the antenna trace length. This reduces
parasitic capacitance and hence reduces coupling into the antenna by noise sources. This
recommendation must be followed for optimal device performance.
Place ESD U3 as close as possible to the whip antenna for maximum effectiveness.
Select ESD diode U3 with minimum capacitance.
Place the ac coupling capacitor, C5, as close to the FMI pin as possible.
Rev. 0.2
29
AN555
6. Ferrite Loop Antenna for AM Receive
Two types of antenna will work well for an AM receiver: a ferrite loop antenna or an air loop antenna. A ferrite loop
antenna can be placed internally on the device or connected externally to the device with a wire connection. When
the ferrite loop antenna is placed internally on the device, it is more susceptible to picking up any noise within the
device. When the ferrite loop antenna is placed outside a device, e.g., at the end of an extension cable, it is less
prone to device noise activity and may result in better AM reception.
6.1. Ferrite Loop Antenna Design
The following figure shows an example of ferrite loop antennas. The left figure is the standard size ferrite loop
antenna, which is usually used in products with a lot of space, such as desktop radios. The right figure is the
miniature size of the loop antenna compared with a U.S. 10-cent piece (dime). It is usually used in small products
where space is at a premium, such as cell phones. If possible, use the standard size ferrite loop antenna as it has
a better sensitivity than the miniature one.
Figure 18. Standard and Miniature Ferrite Loop Antennas
A loop antenna with a ferrite inside should be designed such that the inductance of the ferrite loop is between 180
and 450 uH for the Si483x-B/Si4820/24 AM Receiver.
Table 16 lists the recommended ferrite loop antenna for the Si483x-B/Si4820/24 AM Receiver.
Table 16. Recommended Ferrite Loop Antenna
Part #
Diameter
Length
Turns
Ui
Type
Application
SL8X50MW70T
8 mm
50 mm
70
400
Mn-Zn
Desktop Radios
SL4X30MW100T
4 mm
30 mm
100
300
Ni-Zn
Portable Radios
(MP3, Cell, GPS)
SL3X30MW105T
3 mm
30 mm
105
300
Ni-Zn
SL3X25MW100T
3 mm
25 mm
110
300
Ni-An
SL5X7X100MW70T
5x7 mm
100 mm
70
400
Mn-Zn
The following is the vendor information for the ferrite loop antennas:
Jiaxin Electronics
Shenzhen Sales Office
email:
[email protected]
Web:
www.firstantenna.com
30
Rev. 0.2
Desktop Radios
AN555
6.2. Ferrite Loop Antenna Schematic
Figure 19. AM Ferrite Loop Antenna Schematic
C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 µF.
D1 is an optional ESD diode if there is an exposed pad going to the AMI pin.
6.3. Ferrite Loop Antenna Bill of Materials
Table 17. Ferrite Loop Antenna Bill of Materials
Designator
Description
ANT1
Ferrite loop antenna, 180–450 H
C1
AC coupling capacitor, 0.47 µF, 10%, Z5U/X7R
D1*
ESD diode, IC, SM, SOT23-3,
California Micro Devices, CM1213-01ST
*Note: Optional; only needed if there is any exposed pad going to the AMI pin.
6.4. Ferrite Loop Antenna Layout
Place the chip as close as possible to the ferrite loop antenna feedline. This will minimize the trace going to the
ferrite antenna, which will minimize parasitic capacitance as well as the possibility of noise sources coupling to the
trace.
The placement of the AM antenna is critical because AM is susceptible to noise sources causing interference in the
AM band. Noise sources can come from clock signals, switching power supply, and digital activities (e.g., MCU).
When the AM input is interfaced to a ferrite loop stick antenna, the placement of the ferrite loop stick antenna is
critical to minimize inductive coupling. Place the ferrite loop stick antenna as far away from interference sources as
possible. In particular, make sure the ferrite loop stick antenna is away from signals on the PCB and away from
even the I/O signals of the chip. Do not route any signal under or near the ferrite loop stick. Route digital traces in
between ground plane for best performance. If that is not possible, route digital traces on the opposite side of the
chip. This will minimize capacitive coupling between the plane(s) and the antenna.
To tune correctly, the total capacitance seen at the AMI input needs to be minimized and kept under a certain value.
The total acceptable capacitance depends on the inductance seen by the chip at its AM input. The acceptable
capacitance at the AM input can be calculated using the formula shown in Equation 3.
Rev. 0.2
31
AN555
1
C Total = ------------------------------------------------2
 2f max  L effective
Where:
C Total = Total capacitance at the AMI input
L effective = Effective inductance at the AMI input
f max = Highest frequency in AM band
Equation 3. Expected Total Capacitance at AMI
The total allowable capacitance, when interfacing a ferrite loop stick antenna, is the effective capacitance resulting
from the AMI input pin, the capacitance from the PCB, and the capacitance from the ferrite loop stick antenna. The
inductance seen at the AMI in this case is primarily the inductance of the ferrite loop stick antenna. The total
allowable capacitance in the case of an air loop antenna is the effective capacitance resulting from the AMI input
pin, the capacitance of the PCB, the capacitance of the transformer, and the capacitance of the air loop antenna.
The inductance in this case should also take all the elements of the circuit into account. The input capacitance of
the AMI input is 8 pF. The formula shown in Equation 3 gives a total capacitance of 29 pF when a 300 uH ferrite
loop stick antenna is used for an AM band with 10 kHz spacing, where the highest frequency in the band is
1750 kHz.
6.5. Ferrite Loop Antenna Design Checklist
Place
the chip as close as possible to the ferrite loop antenna feedline to minimize parasitic capacitance
and the possibility of noise coupling.
Place the ferrite loop stick antenna away from any sources of interference and even away from the I/O
signals of the chip. Make sure that the AM antenna is as far away as possible from circuits that switch at a
rate which falls in the AM band (504–1750 kHz).
Recommend keeping the AM ferrite loop antenna at least 5 cm away from the tuner chip.
Place optional component D1 if the antenna is exposed.
Select ESD diode D1 with minimum capacitance.
Do Not Place any ground plane under the ferrite loop stick antenna if the ferrite loop stick antenna is
mounted on the PCB. The recommended ground separation is 1/4 inch or the width of the ferrite.
Route traces from the ferrite loop stick connectors to the AMI input via the ac coupling cap C1 such that the
capacitance from the traces and the pads is minimized.
32
Rev. 0.2
AN555
7. Air Loop Antenna for AM
An air loop antenna is an external AM antenna (because of its large size) typically found on home audio
equipment. An air loop antenna is placed external to the product enclosure making it more immune to system noise
sources. It also will have a better sensitivity compared to a ferrite loop antenna.
7.1. Air Loop Antenna Design
Figure 20 shows an example of an air loop antenna.
Figure 20. Air Loop Antenna
Unlike a ferrite loop, an air loop antenna will have a smaller equivalent inductance because of the absence of ferrite
material. A typical inductance is on the order of 10 to 20 uH. Therefore, in order to interface with the air loop
antenna properly, a transformer is required to raise the inductance into the 180 to 450 uH range.
T1 is the transformer to raise the inductance to within 180 to 450 uH range. A simple formula to use is as follows:
Typically a transformer with a turn ratio of 1:5 to 1:7 is good for an air loop antenna of 10 to 20 uH to bring the
inductance within the 180 to 450 uH range.
Choose a high-Q transformer with a coupling coefficient as close to 1 as possible and use a multiple strands Litz
wire for the transformer winding to reduce the skin effect. All of this will ensure that the transformer will be a low
loss transformer.
Finally, consider using a shielded enclosure to house the transformer or using a torroidal shape core to prevent
noise pickup from interfering sources.
A few recommended transformers are listed in Table 18.
Rev. 0.2
33
AN555
Table 18. Recommended Transformers
Transformer 1
Transformer 2
Transformer 3
Vendor
Jiaxin Electronics
UMEC
UMEC
Part Number
SL9x5x4MWTF1
TG-UTB01527S
TG-UTB01526
Surface Mount
Surface Mount
Through Hole
Primary Coil Turns (L1)
12T
10T
10T
Secondary Coil Turns
(L2)
70T
55T
58T
ULSA / 0.07 mm x 3
n/a
n/a
Type
Wire Gauge
Inductance (L2)
380 µH ±10% @ 796 kHz
Q
184 µH min, 245 µH typ @ 179 µH min, 263 µH typ @
100 kHz
100 kHz
130
50
The following is the vendor information for the above transformer:
Vendor #1:
Jiaxin Electronics
Shenzhen Sales Office
email:
[email protected]
Web:
www.firstantenna.com
Vendor #2:
UMEC USA, Inc.
Website:
www.umec-usa.com
www.umec.com.tw
34
Rev. 0.2
75
AN555
7.2. Air Loop Antenna Schematic
Figure 21. AM Air Loop Antenna Schematic
C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 uF.
D1 is a required ESD diode since the antenna is exposed.
7.3. Air Loop Antenna Bill of Materials
Table 19. Air Loop Antenna Bill of Materials
Designator
Description
LOOP_ANTENNA
Air loop antenna
T1
Transformer, 1:6 turns ratio
C1
AC coupling capacitor, 0.47 µF, 10%, Z5U/X7R
D1
ESD diode, IC, SM, SOT23-3,
California Micro Devices, CM1213-01ST
7.4. Air Loop Antenna Layout
Place the chip and the transformer as close as possible to the air loop antenna feedline. This will minimize the
trace going to the air loop antenna, which will minimize parasitic capacitance and the possibility of noise coupling.
When an air loop antenna with a transformer is used with the Si483x-B/Si4820/24, minimize inductive coupling by
making sure that the transformer is placed away from all sources of interference. Keep the transformer away from
signals on the PCB and away from even the I/O signals of the Si483x-B/Si4820/24. Do not route any signals under
or near the transformer. Use a shielded transformer if possible.
7.5. Air Loop Antenna Design Checklist
Select
a shielded transformer or a torroidal shape transformer to prevent noise pickup from interfering
sources
Select a high-Q transformer with coupling coefficient as close to 1 as possible
Use multiple strands Litz wire for the transformer winding
Place the transformer away from any sources of interference and even away from the I/O signals of the
chip. Make sure that the AM antenna is as far away as possible from circuits that switch at a rate which
falls in the AM band (504–1750 kHz).
Route traces from the transformer to the AMI input via the ac coupling cap C1 such that the capacitance
from the traces and the pads is minimized.
Select ESD diode D1 with minimum capacitance.
Rev. 0.2
35
AN555
8. Whip Antenna for SW Receiver
SW reception usually uses whip antennas, the same as FM.
8.1. SW Whip Antenna Design
A whip antenna is a monopole antenna with a stiff but flexible wire mounted vertically with one end adjacent to the
ground plane.
There are various types of whip antennas, including long non-telescopic metal whip antennas, telescopic metal
whip antennas, and rubber whip antennas. Figure 22 shows the telescopic whip antenna.
Figure 22. Telescopic Whip Antenna for SW
8.2. SW Whip Antenna Schematic
Figure 23. SW Whip Antenna Schematic
Q1 2SC9018 is a low noise RF transistor and it constitutes a LNA to amplify the SW signal coming from the whip
antenna.
C30 (33nF) is the ac couplijng cap between whip antenna and LNA input.
C33 (0.47uF) is the ac coupling cap going to the AMI pin.
R31, R41 are bias resistors of the transistor.
36
Rev. 0.2
AN555
8.3. SW Whip Antenna Bill of Materials
Table 20. SW Whip Antenna Bill of Materials
Designator
Description
WHIP_ANTENNA
Whip Antenna
Q1
Low noise RF transistor, 2SC9018
C30
AC coupling capacitor,
33 nF, 10%, COG
C33
Coupling capacitor, 0.47 µF, ±20%, Z5U/X7R
R31
Resistor, 1 k, ±5%
R41
Resistor, 200 k, ±5%
8.4. SW Whip Antenna Layout
Place the chip and 2SC9018 as close as possible to the whip antenna feedline. This will minimize the trace going
to the whip antenna, which will minimize parasitic capacitance as well as the possibility of noise sources coupling to
the trace.
8.5. SW Whip Antenna Design Checklist
Maximize
whip antenna length for optimal performance.
Q1 and whip antenna close together and as far from potential noise sources as possible to reduce
capacitive and inductive coupling.
Place the chip as close as possible to the whip antenna to minimize the antenna trace length. This reduces
parasitic capacitance and hence reduces coupling into the antenna by noise sources. This
recommendation must be followed for optimal device performance.
Place the ac coupling capacitor C33, as close to the AMI pin as possible.
Place
Rev. 0.2
37
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