AN738: Si4825/36-A Antenna, Schematic, Layout and Design Guidelines

AN738
Si4825/36-A A NTENNA , S CHEMATIC , L AYOUT , AND
D E S I G N G UIDEL INES
1. Introduction
This document provides general Si4825/36-A design and AM/FM/SW antenna selection guidelines, including
schematic, BOM and PCB layout. All users should follow the Si4825/36-A design guidelines presented in Section 2
and Section 3, and choose the appropriate antennas based on the applications and device used according to
Section 4 through 8.
AM Antenna
FM Antenna
Function
†Part
Number
SW Antenna
Table 1. Part Selection Guide
FM Receiver
AM Receiver
SW Receiver
Headphone
Whip
Ferrite Loop
Air Loop
Whip
†General Description
Si4825
Entry Level Wheel-tuned AM/FM/SW
Receiver, Mono Audio
†
†
†
†
†
†
†
†
Si4836
Wheel-tuned AM/FM/SW Receiver,
Stereo Audio
†
†
†
†
†
†
†
†
The purpose of this revision of AN738 is to cover the support for Si4825/36-A20, which is derived from Si4825/36A10. Si4825/36-A20 differs from Si4825/36-A10 in the following two ways:
Extending
the band range of BAND 11 and BAND 12 from 76-90 MHz to 76-95 MHz, details in Section 2.1;
Removing the audio volume/bass/treble settings memorizing and restoring feature, details in Section 3.4.
In this document, if not otherwise specified, Si4825/36-A refers to all the A versions of Si4825/36, including Si4825/
36-A10 and Si4825/36-A20.
Rev. 0.3 3/16
Copyright © 2016 by Silicon Laboratories
AN738
AN738
2. Frequency Band Definition and Selection
Eighteen FM bands, five AM bands, and eighteen SW bands are defined for Si4825/36-A. In FM band, the parts
also offer two de-emphasis selections and two stereo LED indication threshold selections. In SW band, the part
offers 18 wide bands or 18 narrow bands. This section shows the detailed band definition and selection
information.
2.1. Band Definition
For the Si4825/36-A, the FM band definition is a combination of frequency range, de-emphasis and stereo LED
indication threshold (Si4836-A only). Customers should choose the band according to the frequency range, as well
as de-emphasis setting and stereo LED indication requirements. For AM and SW, simply choose the band
according to the frequency range desired.
Table 2. Band Sequence Definition for Si4836-A
2
Band
Number
Band
Name
Band Frequency Range
De-emphasis
(FM)
Channel
Space (AM)
Stereo LED on Conditions
Total R
to GND
(k, 1%)
Band1
FM1
87–108 MHz
50 µs
Separation = 6 dB, RSSI = 20
47
Band2
FM2
87–108 MHz
50 µs
Separation = 12 dB,
RSSI = 28
57
Band3
FM3
87–108 MHz
75 µs
Separation = 6 dB, RSSI = 20
67
Band4
FM4
87–108 MHz
75 µs
Separation = 12 dB,
RSSI = 28
77
Band5
FM5
86.5–109 MHz
50 µs
Separation = 6 dB, RSSI = 20
87
Band6
FM6
86.5–109 MHz
50 µs
Separation = 12 dB,
RSSI = 28
97
Band7
FM7
87.3–108.25 MHz
50 µs
Separation = 6 dB, RSSI = 20
107
Band8
FM8
87.3–108.25 MHz
50 µs
Separation = 12 dB,
RSSI = 28
117
Band9
FM9
87.3–108.25 MHz
75 µs
Separation = 6 dB, RSSI = 20
127
Band10
FM10
87.3–108.25 MHz
75 µs
Separation = 12 dB,
RSSI = 28
137
Band11
FM11
76–90 MHz (Si4836-A10)
76–95 MHz (Si4836-A20)
50 µs
Separation = 6 dB, RSSI = 20
147
Band12
FM12
76–90 MHz (Si4836-A10)
76–95 MHz (Si4836-A20)
50 µs
Separation = 12 dB,
RSSI = 28
157
Band13
FM13
64–87 MHz
50 µs
Separation = 6 dB, RSSI = 20
167
Band14
FM14
64–87 MHz
50 µs
Separation = 12 dB,
RSSI = 28
177
Band15
FM15
76–108 MHz
50 µs
Separation = 6 dB, RSSI = 20
187
Band16
FM16
76–108 MHz
50 µs
Separation = 12 dB,
RSSI = 28
197
Rev. 0.3
AN738
Table 2. Band Sequence Definition for Si4836-A (Continued)
Band
Number
Band
Name
Band Frequency Range
De-emphasis
(FM)
Channel
Space (AM)
Stereo LED on Conditions
Total R
to GND
(k, 1%)
Band17
FM17
64–108 MHz
50 µs
Separation = 6 dB, RSSI = 20
207
Band18
FM18
64–108 MHz
50 µs
Separation = 12 dB,
RSSI = 28
217
Band19
AM1
520–1710 kHz
10 k
227
Band20
AM2
522–1620 kHz
9k
237
Band21
AM3
504–1665 kHz
9k
247
Band22
AM4
522–1728 kHz /
520–1730 kHz
9 k / 10 k
257
Band23
AM5
510–1750 kHz
10 k
267
Band24
SW1
SW Wide Band SW Narrow Band
277
2.3–10.0 MHz
2.30–2.49 MHz
Band25
SW2
3.2–7.6 MHz
3.20–3.40 MHz
287
Band26
SW3
3.2–10.0 MHz
3.90–4.00 MHz
297
Band27
SW4
3.7–12.5 MHz
4.75–5.06 MHz
307
Band28
SW5
3.9–7.5 MHz
5.6–6.4 MHz
317
Band29
SW6
5.6–22 MHz
5.95–6.2 MHz
327
Band30
SW7
5.8–12.1 MHz
6.8–7.6 MHz
337
Band31
SW8
5.9–9.50 MHz
7.1–7.6 MHz
347
Band32
SW9
5.9–18.0 MHz
9.2–10 MHz
357
Band33
SW10
7.0–16.0 MHz
11.45–
12.25 MHz
367
Band34
SW11
7.0– 23.0 MHz
11.6–12.2 MHz
377
Band35
SW12
9.0–16.0 MHz
13.4–14.2 MHz
387
Band36
SW13
9.0–22.0 MHz
13.57–
13.87 MHz
397
Band37
SW14
9.5–18.0 MHz
15–15.9 MHz
407
Band38
SW15
10.0–16.0 MHz
17.1–18 MHz
417
Band39
SW16
10.0–22.0 MHz 17.48–17.9 MHz
427
Band40
SW17
13.0–18.0 MHz
21.2–22 MHz
437
Band41
SW18
18.0–28.5 MHz
21.45–
21.85 MHz
447
Rev. 0.3
3
AN738
Table 3. Band Sequence Definition for Si4825-A
4
Band Frequency Range
De-emphasis
(FM)
Channel Space
(AM)
Total R
to GND
(kΩ, 1%)
87–108 MHz
50 µs
57
87–108 MHz
75 µs
77
86.5–109 MHz
50 µs
97
87.3–108.25 MHz
50 µs
117
87.3–108.25 MHz
75 µs
137
76–90 MHz (Si4825-A10)
76–95 MHz (Si4825-A20)
50 µs
157
64–87 MHz
50 µs
177
76–108 MHz
50 µs
197
64–108 MHz
50 µs
217
AM1
520–1710 kHz
10 K
227
Band20
AM2
522–1620 kHz
9K
237
Band21
AM3
504–1665 kHz
9K
247
Band22
AM4
522–1728 kHz /
520–1730 kHz
9 K/10 K
257
Band
Number
Band
Name
Band1
FM1
Band2
FM2
Band3
FM3
Band4
FM4
Band5
FM5
Band6
FM6
Band7
FM7
Band8
FM8
Band9
FM9
Band10
FM10
Band11
FM11
Band12
FM12
Band13
FM13
Band14
FM14
Band15
FM15
Band16
FM16
Band17
FM17
Band18
FM18
Band19
Rev. 0.3
AN738
Table 3. Band Sequence Definition for Si4825-A (Continued)
Band
Number
Band
Name
Band Frequency Range
De-emphasis
(FM)
Channel Space
(AM)
Total R
to GND
(kΩ, 1%)
Band23
AM5
510–1750 kHz
10 K
267
SW Wide Band
SW Narrow Band
2.3–10.0 MHz
2.30–2.49 MHz
Band24
SW1
Band25
SW2
3.2–7.6 MHz
3.20–3.40 MHz
287
Band26
SW3
3.2–10.0 MHz
3.90–4.00 MHz
297
Band27
SW4
3.7–12.5 MHz
4.75–5.06 MHz
307
Band28
SW5
3.9–7.5 MHz
5.6–6.4 MHz
317
Band29
SW6
5.6–22 MHz
5.95–6.2 MHz
327
Band30
SW7
5.8–12.1 MHz
6.8–7.6 MHz
337
Band31
SW8
5.9–9.50 MHz
7.1–7.6 MHz
347
Band32
SW9
5.9–18.0 MHz
9.2–10 MHz
357
Band33
SW10
7.0–16.0 MHz
11.45–12.25 MHz
367
Band34
SW11
7.0–23.0 MHz
11.6–12.2 MHz
377
Band35
SW12
9.0–16.0 MHz
13.4–14.2 MHz
387
Band36
SW13
9.0–22.0 MHz
13.57–13.87 MHz
397
Band37
SW14
9.5–18.0 MHz
15–15.9 MHz
407
Band38
SW15
10.0–16.0 MHz
17.1–18 MHz
417
Band39
SW16
10.0–22.0 MHz
17.48–17.9 MHz
427
Band40
SW17
13.0–18.0 MHz
21.2–22 MHz
437
Band41
SW18
18.0–28.5 MHz
21.45–21.85 MHz
447
Rev. 0.3
277
5
AN738
2.2. Band Selection
Refer to Figure 1 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
Table 4 and Figure 1 illustrate the band and resistor value details for a typical 12-band application for Si4836-A.
.
Table 4. Typical 12-Band Selection
Band
Band
Number Name
Band Frequency Range
De-emphasis (FM)
Channel Space
(AM)
Stereo LED on
Conditions (Only for
Si4836-A)
Total R to
GND (K,
1%)
Band3
FM3
87–108 MHz
75 µs
Separation = 6 dB,
RSSI = 20
67
Band17
FM17
64–108 MHz
50 µs
Separation = 6 dB,
RSSI = 20
207
Band19
AM1
520–1710 kHz
10 k
227
Band20
AM2
522–1620 kHz
9k
237
Band25
SW2
SW Wide
Band
SW Narrow Band
3.2–7.6 MHz
3.20–3.40 MHz
287
Band26
SW3
3.2–10.0 MHz
3.90–4.00 MHz
297
Band32
SW9
5.9–18.0 MHz
9.2–10 MHz
357
Band33
SW10 7.0–16.0 MHz 11.45–12.25 MHz
367
Band34
SW11 7.0–23.0 MHz
377
Band36
SW13 9.0–22.0 MHz 13.57–13.87 MHz
397
Band37
SW14 9.5–18.0 MHz
15–15.9 MHz
407
Band39
SW16
17.48–17.9 MHz
427
6
10.0–
22.0 MHz
11.6–12.2 MHz
Rev. 0.3
AN738
Figure 1. Typical 12-Band Selection Circuit
Rev. 0.3
7
AN738
2.2.2. Typical 2-band Application for Europe
Table 5 and Figure 2 show the band and resistor value details for a typical European 2-band application.
Table 5. Typical European 2-Band Selection
Band
Number
Band
Name
Band Frequency
Range
De-emphasis (FM)
Channel Space (AM)
Band2
FM2
87–108 MHz
50 µs
Band20
AM2
522–1620 kHz
9k
Stereo LED on
Conditions
(Only for Si4836-A)
Separation = 12 dB,
RSSI = 28
R3
263k, 1%
S2
1
AM
2
3
R4
180k, 1%
FM
R5
57k, 1%
Figure 2. Typical 2-Band Selection Circuit for Europe
8
Rev. 0.3
57
237
TUNE1
BAND
Total R to GND
(k, 1%)
AN738
2.2.3. Typical 2-band Application for US
Table 6 and Figure 3 show the band and resistor value details for a typical 2-band application for the U.S.
Table 6. Typical U.S. 2-Band Selection
Band
Number
Band
Name
Band Frequency
Range
De-emphasis
Band4
FM4
87–108 MHz
75 µs
Band19
AM1
520–1710 kHz
10 k
Stereo LED on
Threshold
(Only for Si483x-A)
Separation = 12 dB,
RSSI = 28
Total R to GND
(k, 1%)
77
227
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Rev. 0.3
9
AN738
3. Si4825/36-A SOIC Schematic and Layout
This section shows the typical schematic and layout required for optimal Si4825/36-A performance.
The Si4825/36-A offers eighteen wide SW bands or eighteen narrow SW bands. The wide/narrow SW bands are
selected via an external pin pull up/down resistor, as illustrated in Figure 4. The Si4825-A configures the Pin 1 as
the wide/narrow SW band selection pin. As the chip integrates about 50 k internal pull down resistor for Pin 1, the
external pull down resistor is omitted. The Si4836-A configures Pin 11 as the wide/narrow SW band selection pin.
Figure 4. Si4825/36-A SW Wide/Narrow Band Selection
3.1. Si4825/36-A Basic Applications Circuits
Figure 5 and Figure 6 are the Si4825/36-A basic application circuits for typical 12-band FM/AM/SW radios.
C16 and C15 are required bypass capacitors for VDD power supply Pin 14. Place C16 and C15 as close as
possible to the VDD Pin 14. This placement will reduce the size of the current loop created by the bypass cap and
routing, minimize bypass cap impedance, and return all currents to GND.
Pin 15 is the GND of the chip; it must be well connected to the power supply GND on PCB.
Pin 7 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 (4.7 µF) are ac coupling caps for receiver analog audio output from Pin 1 and/or Pin 16. 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.
10
Rev. 0.3
AN738
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 12 and XTALI Pin 13 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 5; do not route Pin 5. This pin must be left floating to
guarantee proper operation.
Pin 10, 11 are volume control pins for Si4825-A or stereo/station pin for Si4836-A, for using tuner internal volume
control function or stereo/station indicator function.
VR1 (100k /10%), R27, C1, C13 constitute the tuning circuit. 100K at 10% tolerance is recommended for VR1.
1P12T switch S2 together with resistor ladder constitutes band select circuits. Si4825/36-A includes all AM, FM,
and SW bands as defined in Section “2.1. Band Definition” .
Q1(2SC9018), together with it's peripherals B6, C30,31,33,36, R31,32,34,41 constitute the LNA circuit for all SW
bands. The LNA is switched off by the LNA_EN signal in AM and FM mode controlled by the chip.
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Figure 5. Si4825-A Basic Applications Circuit
Rev. 0.3
11
AN738
Figure 6. Si4836-A Basic Applications Circuit
12
Rev. 0.3
AN738
3.2. Si4825-A Applications Circuit with Internal Volume Adjustment via 2 Push Buttons
The Si4825-A supports internal volume adjustment via two push buttons. Figure 7 is the Si4825-A applications
circuit with internal volume adjustment. 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, the tuner volume will step through all levels until reaching
the minimum or maximum, respectively.
The chip Si4836-A works without internal volume adjustment. Volume control can be performed at the audio
amplifier circuit stage.
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Figure 7. Si4825-A Applications Circuit with Internal Volume Adjustment
At the device powerup, Si4825-A will put the output volume at some default levels according to the push button
configurations as shown in Figure 8. The Si4825-A has four default volume level choices. Adding pull-down
resistors to both Pin 10 and 11 sets the default volume to maximum, typically 80 mVrms for FM and 60 mVrms for
AM. Different Pin 10 and 11 pull-up/down resistor combinations can set the default volume to either Max, Max6 dB, Max-12 dB or Max-18 dB. For example in Figure 5, two pull-down resistors are connected to Pin 10 and Pin
11, which sets the default volume to Max.
Rev. 0.3
13
AN738
Figure 8. Si4825-A Default Volume Selection
3.3. Si4836-A Applications Circuit with Bass/Treble Control via 1 Push Button
The Si4836-A further supports bass and treble tone control for superior sound quality. When the tuner uses the
external reference clock RCLK, Pin 12 can be configured for tone control with the push button for cyclic switching
of three tone levels (bass/normal/treble). If the user does not want to use the bass/treble tone control, Pin 12 must
be connected to a 56k external pull down resistor. When the tuner uses the crystal, the user cannot use the bass/
treble control.
Figure 8 is the Si4836-A applications circuit with bass/treble tone control. Push button S3 controls the bass/treble
effect.
14
Rev. 0.3
Figure 9. Si4836-A Applications Circuit with Bass/Treble Control
AN738
Rev. 0.3
15
AN738
3.4. Application Circuits for Memorizing User Settings
The Si4825/36-A has high retention memory (HRM) built-in that can memorize the user settings.
The Si4825/36-A10 memorizes the last volume/bass/treble settings so that at the next power up, the unit will
automatically restore the volume and bass/treble settings to those before the last power off. If the user does not
use the HRM, the tuner will restore the default volume/bass/treble setting at each power up.
Both Si48325/36-A10 and Si4825/36-A20 memorize the last tuned station before power off and restore 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. This restoration process will improve the tuned channel consistency before power off and after
power on.
To memorize the user settings, Pin 14 VDD needs to be connected to an always-on power source. Force Pin 9
RSTB voltage to below 0.3*VDD to power off Si4825/36.
In Figure 10, the Pin 14 VDD is connected to battery VBAT. A 2P2T power on/off switch S3 is recommended one
pole of S3 short Pin 9 RSTB to GND to power off the tuner.
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Figure 10. Si4825-A Applications Circuit with User Setting Memory
16
Rev. 0.3
AN738
3.5. Si4825/36-A Bill of Materials
3.5.1. Si4825-A Basic Applications Circuit BOM
Table 7. Si4825-A Basic Applications Circuit BOM
Component(s)
Value/Description
Supplier
C4,C15
Capacitor 4.7 F, ±20%, Z5U/X7R
Murata
C13
Capacitor 47 F, ±20%, Z5U/X7R
Murata
C1,C6,C19
Supply bypass capacitor, 0.1 F, ±20%, Z5U/X7R
Murata
C5,C36
Supply bypass capacitor, 0.47 F, ±20%, Z5U/X7R
Murata
C34
RF coupling capacitors, 33 pF, ±5%, COG
Murata
C33
Capacitor capacitors,10 pF, ±5%, COG
Murata
C30,C31
Capacitor capacitors,33 nF, ±5%, COG
Murata
VR1
Variable resistor (POT), 100 k, ±10%
Changtaier
U1
Si4825-A AM/FM/SW Analog Tune Analog Display Radio Tuner
Silicon
Laboratories
R32
Resistor, 10 , ±5%
R27
Resistor, 100 , ±5%
Venkel
R31
Resistor, 1 k, ±5%
Venkel
R17
Resistor, 10 k, ±5%
Venkel
R6,R34
Resistor, 100 k, ±5%
Venkel
R41
Resistor, 120 k, ±5%
Venkel
R7,R9,R11,R12,R15,
R28
Band switching resistor, 10 k, ±1%
Venkel
R43
Band switching resistor, 40 k, ±1%
Venkel
R44
Band switching resistor, 47 k, ±1%
Venkel
R36
Band switching resistor, 33 k, ±1%
Venkel
R29
Band switching resistor, 140 k, ±1%
Venkel
R10,R35
Band switching resistor, 20 k, ±1%
Venkel
R8
Band switching resistor, 50 k, ±1%
Venkel
Rev. 0.3
17
AN738
Table 7. Si4825-A Basic Applications Circuit BOM (Continued)
Component(s)
Value/Description
Supplier
R14
Band switching resistor, 60 k, ±1%
Venkel
R33
Band switching resistor, 30 k, ±1%
Venkel
S2
Band switch
Shengda
J8
Slider switch
Shengda
B6
Ferrite bead,2.5K/100 MHz
Murata
Q1
RF transistor,2SC9018
ETC
ANT2
Whip antenna
Various
ANT1
MW ferrite antenna 220 H
Jiaxin Electronics
Optional
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
3.5.2. Additional BOM for Si4825-A Applications Circuit with Internal Volume Adjustment
Table 8. Additional BOM for Si4825-A Applications Circuit with Internal Volume Adjustment
Component(s)
Value/Description
Supplier
R37, R38
Resistor, 56 k, ±5%
Venkel
S3, S4
Push button
Various
3.5.3. Additional BOM for Si4825-A Applications Circuit with User Setting Memory
Table 9. Additional BOM for Si4825-A Applications Circuit with User Setting Memory
18
Component(s)
Value/Description
Supplier
R37,R38
Resistor, 56 k, ±5%
Venkel
S3, S4
Push button
Various
S1
2P2T slide switch
Shengda
R45
Resistor, 200 , ±5%
Venkel
C14
Supply bypass electrolytic capacitor, 100 µF, 4V
Various
C39
Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R
Murata
Rev. 0.3
AN738
3.5.4. Si4836-A Basic Applications Circuit BOM
Table 10. Si4836-A Basic 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,C16,C19
Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R
Murata
C5,C36
Supply bypass capacitor, 0.47 µF, ±20%, Z5U/X7R
Murata
C34
RF coupling capacitors, 33 pF, ±5%, COG
Murata
C33
Capacitor capacitors, 10 pF, ±5%, COG
Murata
C30,C31
Capacitor capacitors, 33 nF, ±5%, COG
Murata
VR1
Variable resistor (POT), 100 k, ±10%
Changtaier
U1
Si4836-A AM/FM/SW Analog Tune Analog Display Radio Tuner
Silicon Laboratories
R32
Resistor, 10 , ±5%
Venkel
R27
Resistor, 100 , ±5%
Venkel
R31
Resistor, 1 k, ±5%
Venkel
R6,R34
Resistor, 100 k, ±5%
Venkel
R41
Resistor, 120 k, ±5%
Venkel
R5,R21
Resistor, 200 , ±5%
Venkel
R1,R2
Resistor, 56 k, ±5%
Venkel
R7,R9,R11,R12,R15
Band switching resistor, 10 k, ±1%
Venkel
R43
Band switching resistor, 40 k, ±1%
Venkel
R44
Band switching resistor, 47 k, ±1%
Venkel
R36
Band switching resistor, 33 k, ±1%
Venkel
R29
Band switching resistor, 140 k, ±1%
Venkel
R10,R28,R33,R35
Band switching resistor, 20 k, ±1%
Venkel
R8
Band switching resistor, 50 k, ±1%
Venkel
R14
Band switching resistor, 60 k, ±1%
Venkel
S2
Band switch
Shengda
J7
Slide switch
Shengda
L2
Inductor 270 nH
Murata
B6
Ferrite bead, 2.5 k/100 MHz
Murata
Rev. 0.3
19
AN738
Table 10. Si4836-A Basic Applications Circuit BOM (Continued)
Component(s)
Value/Description
Supplier
Q1
RF transistor, 2SC9018
ETC
D1,D3
Station and Stereo indicating LEDs
Various
ANT2
Whip antenna
Various
ANT1
MW ferrite antenna 220 µH
Jiaxin Electronics
Optional
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 or equivalent
3.5.5. Additional BOM For Si4836-A Applications Circuit With Bass/Treble Control
Table 11. Additional BOM for Si4836-A Applications Circuit with Bass/Treble Control
Component(s)
20
Value/Description
Supplier
R4
Resistor, 56 k, ±5%
Venkel
C6
Capacitor, 0.1 µF, ±20%, Z5U/X7R
Murata
S3
Push button
Various
Rev. 0.3
AN738
3.6. Si4825/36-A PCB Layout Guidelines
1-layer
PCB is used for Si4825/36-A
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
Place VDD bypass capacitor C16, C15 as close as possible to the power supply pin (Pin 14).
GND
Place the crystal as close to XTALO (Pin 12) and XTALI (Pin 13) 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 5. This pin must be left floating to guarantee proper operation.
Keep the Tune1 and Tune2 traces away from Pin 5, route Tune1 and Tune2 traces in parallel and the same way.
Place C1, C13 as close to Pin 2 TUNE1 as possible.
Refer to the Si4836-A Layout example as much as possible when doing Si4825/36-A PCB layout.
Figure 11. Si4836-A PCB Layout Example
Rev. 0.3
21
AN738
4. Headphone Antenna for FM Receive
The Si4825/36-A 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 at least three 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 12.
Figure 12. Typical Headphone Antenna Application
22
Rev. 0.3
AN738
4.2. Headphone Antenna Schematic
Figure 13. 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 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 13, 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 Si4825/36-A. 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. As Diode D3 may not be relocated, it must 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.
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
Rev. 0.3
23
AN738
greater; however, the designer should confirm that the headphone amplifier is capable of driving the selected shunt
capacitance.
The schematic example in Figure 13 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 are 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 = ----------------------------------- , ----------------------------------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 also can be shut down by
applying a logic low voltage to Pin 3. 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 13 is provided in Table 12. Note that
manufacturer is not critical for resistors and capacitors.
4.3. Headphone Antenna Bill of Materials
Table 12. Headphone Antenna Bill of Materials
24
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 µF, 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. 0.3
AN738
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 closely as possible to the headphone connector.
To maximize ESD protection diode effectiveness, place diodes D1, D2, and D3 as near to the headphone
connector as possible. 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 near to the headphone connector as possible 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. 0.3
25
AN738
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 14 shows the telescopic whip antenna.
Figure 14. 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 15. 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 (1 nF) 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.
26
Rev. 0.3
AN738
5.3. FM Whip Antenna Bill of Materials
Table 13. 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 near to the whip antenna as possible. 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 near 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. 0.3
27
AN738
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 16. 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 Si4825/36-A AM Receiver.
Table 14 lists the recommended ferrite loop antenna for the Si4825/36-A AM Receiver.
Table 14. 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
28
Rev. 0.3
Desktop Radios
AN738
6.2. Ferrite Loop Antenna Schematic
Figure 17. 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 15. Ferrite Loop Antenna Bill of Materials
Designator
Description
ANT1
Ferrite loop antenna, 180–450 µH
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. 0.3
29
AN738
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 28 pF when a 300 uH ferrite
loop stick antenna is used for an AM band, 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.
30
Rev. 0.3
AN738
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 18 shows an example of an air loop antenna.
Figure 18. 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 µH. Therefore, in order to interface with the air loop
antenna properly, a transformer is required to raise the inductance into the 180 to 450 µH range.
T1 is the transformer to raise the inductance to within 180 to 450 µH range. A simple formula to use is as follows:
2
L equivalent = N L AIRLOOP
Typically a transformer with a turn ratio of 1:5 to 1:7 is good for an air loop antenna of 10 to 20 µH to bring the
inductance within the 180 to 450 µH 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 16.
Rev. 0.3
31
AN738
Table 16. 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
184 µH min, 245 µH typ @ 179 µH min, 263 µH typ @
100 kHz
100 kHz
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
32
Rev. 0.3
AN738
7.2. Air Loop Antenna Schematic
Figure 19. AM Air Loop Antenna Schematic
C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 µF.
D1 is a required ESD diode since the antenna is exposed.
7.3. Air Loop Antenna Bill of Materials
Table 17. 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 Si4825/36-A, 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 Si4825/36-A. 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. 0.3
33
AN738
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 20 shows the telescopic whip antenna.
Figure 20. Telescopic Whip Antenna for SW
8.2. SW Whip Antenna Schematic
Figure 21. 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 (33 nF) is the ac couplijng cap between whip antenna and LNA input.
C33 (0.47 µF) is the ac coupling cap going to the AMI pin.
R31, R41 are bias resistors of the transistor.
34
Rev. 0.3
AN738
8.3. SW Whip Antenna Bill of Materials
Table 18. 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. 0.3
35
AN738
DOCUMENT CHANGE LIST
Revision 0.1 to Revision 0.2

Added new Table 3 for the band definition of Si4825A.
 Updated all the Si4825 schematic figures and the
BOM tables.
Revision 0.2 to Revision 0.3

Updated the band definition Table 2 and Table 3 to
support Si4825/36-A20.
 Updated Section“3.4. Application Circuits for
Memorizing User Settings” to support Si4825/36A20.
36
Rev. 0.3
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