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%) 77 227 781( 5 N $0 6 %$1' 5 N )0 5 N Figure 3. Typical 2-Band Selection Circuit for US 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 = --------------2RC 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. 781( 5 N $17 5 N 781( & X 6:1DUURZ %$1' 6:10+]0+]:0+]0+] 781( /1$B(1 $287 6 8 %$1' 6L$ *1' 781( 9'' %$1' ;7$/, 1& ;7$/2 )0, 92/ $0, 5)*1' 92/ X 567 & $287 6:10+]0+]:0+]0+] 5 N 6:10+]0+]:0+]0+] 5 N 6:10+]0+]:0+]0+] X & 5 N 9&& 5 N S 4 6& 5 N Q - 6:10+]0+]:0+]0+] 5 N & X 9&& & & 5 N 9&& 5 N $17 0:IHUULWHDQWHQQD % N0 5 N 6::LGH & S & Q 5 N 6:10+]0+]:0+]0+] /1$B(1 5 5 5 5 /1$B(1 5 N X 9&& & X 6:10+]0+]:0+]0+] 95 N & 5 N & & X X 6:10+]0+]:0+]0+] 5 N $0N+]N+] 5 < N .+] & S $0N+]N+] & S 5 N )00+]0+] 2SWLRQDO 5 N )00+]0+] 5 N 5 N 1RWH1 6:1DUURZ%DQG: 6::LGH%DQG 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. 781( 5 N $17 5 N 781( & 6:10+]0+]:0+]0+] 95 N & 5 X N X 5 5 N 6:1DUURZ %$1' 6 8 6L$ %$1' $287 /1$B(1 5 N 781( *1' 781( %$1' ;7$/, 1& ;7$/2 9'' )0, $0, 567 5 N X 92/ 4 6& $17 0:IHUULWHDQWHQQD Q 6:10+]0+]:0+]0+] 5 N 6:10+]0+]:0+]0+] S & 5 N & 5)*1' & 92/ 5 N 5 N /1$B(1 - 9&& & S & Q % 6:10+]0+]:0+]0+] 6::LGH 5 5 5 N0 /1$B(1 9&& & X & $287 X X 6 & & X X 5 N 6:10+]0+]:0+]0+] 5 N 6:10+]0+]:0+]0+] N 6:10+]0+]:0+]0+] 5 YROXPH 6 YROXPH 5 N 6:10+]0+]:0+]0+] 5 9&& & 9&& 9&& 9&& N $0N+]N+] < 5 N .+] 5 N 5 N & S $0N+]N+] & S 5 N 2SWLRQDO )00+]0+] 5 N )00+]0+] 5 N 5 N 1RWH1 6:1DUURZ%DQG: 6::LGH%DQG 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. 781( 5 N $17 5 N 781( & & X X 6:10+]0+]:0+]0+] 95 N 5 N 5 5 N 6:1DUURZ & S %$1' 781( /1$B(1 6 8 6L$ %$1' $287 *1' 5 N 781( %$1' ;7$/, 9'' 1& ;7$/2 )0, $0, 567 5 N X 92/ 4 6& $17 0:IHUULWHDQWHQQD Q 6:10+]0+]:0+]0+] 5 N 6:10+]0+]:0+]0+] S & 5 N & 5)*1' & 92/ 5 N 5 N /1$B(1 - 9&& 5 5 % 6:10+]0+]:0+]0+] 6::LGH 5 & Q N0 /1$B(1 9&& & X & $287 X 9&& 6 YROXPH 6 YROXPH 5 N 6:10+]0+]:0+]0+] 5 N 6:10+]0+]:0+]0+] 5 X N 5 9&& 9&& 9%$7 & 6:10+]0+]:0+]0+] N & & X X 6:10+]0+]:0+]0+] 5 5(6(7 N $0N+]N+] < 5 N .+] 5 N 5 N & S $0N+]N+] & S 5 N 2SWLRQDO )00+]0+] 5 5(6(7 N )00+]0+] 6 5 N 9&& 5 5 9%$7 & X & X9 5 N 1RWH1 6:1DUURZ%DQG: 6::LGH%DQG 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 2f 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 Smart. Connected. Energy-Friendly Products Quality www.silabs.com/products www.silabs.com/quality Support and Community community.silabs.com Disclaimer Silicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "Typical" parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. 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