AN555 S i483 X -B/Si4820/24 A NTENNA , S CHEMATIC , L AYOUT , AND D E S I G N G UIDEL INES 1. Introduction This document provides general Si483x-B/Si4820/24 design and AM/FM/SW antenna selection guidelines, including schematic, BOM and PCB layout. All users should follow the Si483x-B/Si4820/24 design guidelines presented in Section 2 and Section 3 and choose the appropriate antennas based on the applications and device used according to Sections 4 through 8. Wheel-tuned AM/FM Receiver † † Si4835-B30 Wheel-tuned AM/FM/SW Receiver † † Si4835-B31 Wheel-tuned AM/FM/SW Receiver, Enhanced SW Tuning Feel † † Si4820-A10 Entry Level Wheel-tuned AM/FM Receiver, Mono Audio † † Si4824-A10 Entry Level Wheel-tuned AM/FM/SW Receiver, Mono Audio † † Rev. 0.2 11/11 Whip Air Loop AM Antenna Ferrite Loop Whip Headphone FM Antenna Si4831-B30 SW Receiver AM Receiver FM Receiver Function †General Description FM Receiver †Part Number SW Antenna Table 1. Part Selection Guide † † † † † † † † † † † † † † † † † † † † † † † † † Copyright © 2011 by Silicon Laboratories † AN555 AN555 2. Frequency Band Definition and Selection Five FM bands and five AM bands are defined for the Si4831-B/Si4820. The Si4835-B/Si4824 has 16 SW bands available. In each FM band, the parts also offer two de-emphasis selections and two LED stereo separation threshold selections, which result in a total of 41 combinations. This section shows the detailed band definition and selection information. 2.1. Band Definition For the Si483x-B/Si4820/24, the FM band definition is a combination of frequency range, de-emphasis and LED stereo separation threshold. Customers should choose the band according to not only frequency range, but also de-emphasis setting and LED stereo separation requirements. For AM and SW, simply choose the band according to the frequency range desired. Table 2. Band Sequence Definition Band Number 2 Band Name Band Frequency Range De-emphasis Stereo LED on Threshold (Only for Si483x-B) Total R to GND (k, 1%) Band1 FM1 87–108 MHz 50 µs Separation = 6 dB, RSSI = 20 47 Band2 FM1 87–108 MHz 50 µs Separation = 12 dB, RSSI = 28 57 Band3 FM1 87–108 MHz 75 µs Separation = 6 dB, RSSI = 20 67 Band4 FM1 87–108 MHz 75 µs Separation = 12 dB, RSSI = 28 77 Band5 FM2 86.5–109 MHz 50 µs Separation = 6 dB, RSSI = 20 87 Band6 FM2 86.5–109 MHz 50 µs Separation = 12 dB, RSSI = 28 97 Band7 FM2 86.5–109 MHz 75 µs Separation = 6 dB, RSSI = 20 107 Band8 FM2 86.5–109 MHz 75 µs Separation = 12 dB, RSSI = 28 117 Band9 FM3 87.3–108.25 MHz 50 µs Separation = 6 dB, RSSI = 20 127 Band10 FM3 87.3–108.25 MHz 50 µs Separation = 12 dB, RSSI = 28 137 Band11 FM3 87.3–108.25 MHz 75 µs Separation = 6 dB, RSSI = 20 147 Band12 FM3 87.3–108.25 MHz 75 µs Separation = 12 dB, RSSI = 28 157 Band13 FM4 76–90 MHz 50 µs Separation = 6 dB, RSSI = 20 167 Band14 FM4 76–90 MHz 50 µs Separation = 12 dB, RSSI = 28 177 Rev. 0.2 AN555 Table 2. Band Sequence Definition (Continued) Band Number Band Name Band Frequency Range De-emphasis Stereo LED on Threshold (Only for Si483x-B) Total R to GND (k, 1%) Band15 FM4 76–90 MHz 75 µs Separation = 6 dB, RSSI = 20 187 Band16 FM4 76–90 MHz 75 µs Separation = 12 dB, RSSI = 28 197 Band17 FM5 64–87 MHz 50 µs Separation = 6 dB, RSSI = 20 207 Band18 FM5 64–87 MHz 50 µs Separation = 12 dB, RSSI = 28 217 Band19 FM5 64–87 MHz 75 µs Separation = 6 dB, RSSI = 20 227 Band20 FM5 64–87 MHz 75 µs Separation = 12 dB, RSSI = 28 237 Band21 AM1 520–1710 kHz 247 Band22 AM2 522–1620 kHz 257 Band23 AM3 504–1665 kHz 267 Band24 AM4 520–1730 kHz 277 Band25 AM5 510–1750 kHz 287 Band26 SW1 5.6–6.4 MHz 297 Band27 SW2 5.95–6.2 MHz 307 Band28 SW3 6.8–7.6 MHz 317 Band29 SW4 7.1–7.6 MHz 327 Band30 SW5 9.2–10 MHz 337 Band31 SW6 9.2–9.9 MHz 347 Band32 SW7 11.45–12.25 MHz 357 Band33 SW8 11.6–12.2 MHz 367 Band34 SW9 13.4–14.2 MHz 377 Band35 SW10 13.57–13.87 MHz 387 Band36 SW11 15–15.9 MHz 397 Band37 SW12 15.1–15.8 MHz 407 Band38 SW13 17.1–18 MHz 417 Band39 SW14 17.48–17.9 MHz 427 Band40 SW15 21.2–22 MHz 437 Band41 SW16 21.45–21.85 MHz 447 Rev. 0.2 3 AN555 2.2. Si483x-B/Si4820/24 Band Selection Refer to Figure 1 below for the band selection circuits. Selecting a band determines the resistance value from the band select pin to GND. To select a specific band, you need to ensure two things: 1. Total value of resistance from the BAND to GND is equal to the value specified in Table 2 2. Total resistance from TUNE1 to GND is 500 k in 1% tolerance The following sections describe some commonly used bands and their respective selection circuits. 2.2.1. Typical 12-band application Figure 1 and Table 3 illustrate the band and resistor value details for a typical 12-band application. 4 Rev. 0.2 AN555 TUNE1 R36 33k 1% R43 30k 1% SW15 (21.2MHz - 22MHz) R35 20k 1% SW13 (17.1MHz - 18MHz) R15 20k 1% SW11 (15MHz - 15.9MHz) Si4835/24 only R10 20k 1% SW9 (13.4MHz - 14.2MHz) R12 20k 1% S2 BAND 1 SW7(11.45MHz - 12.25MHz) 2 3 4 5 6 7 8 9 10 11 12 13 R11 20k 1% SW5(9.2MHz - 10.0MHz) R14 20k 1% SW3(6.8MHz - 7.6MHz) R9 20k 1% SW1 (5.6MHz - 6.4MHz) R8 50k 1% AM1 (520kHz - 1710kHz) R7 20k 1% FM5 (64MHz - 87MHz) R28 40k 1% FM4 (76MHz - 90MHz) R29 120k 1% FM1 (87MHz - 108MHz) R33 20k 1% R44 47k 1% Figure 1. Typical 12-Band Selection Circuit Rev. 0.2 5 AN555 Table 3. Typical 12-Band Selection 6 Band Number Band Name Band Frequency Range De-emphasis Stereo LED on Threshold (Only for Si483x-B) Total R to GND (k, 1%) Band3 FM1 87–108 MHz 75 µs Separation = 6 dB, RSSI = 20 67 Band15 FM4 76–90 MHz 75 µs Separation = 6 dB, RSSI = 20 187 Band19 FM5 64–87 MHz 75 µs Separation = 6 dB, RSSI = 20 227 Band21 AM1 520–1710 kHz 247 Band26 SW1 5.6–6.4 MHz 297 Band28 SW3 6.8–7.6 MHz 317 Band30 SW5 9.2–10 MHz 337 Band32 SW7 11.45–12.25 MHz 357 Band34 SW9 13.4–14.2 MHz 377 Band36 SW11 15–15.9 MHz 397 Band38 SW13 17.1–18 MHz 417 Band40 SW15 21.2–22 MHz 437 Rev. 0.2 AN555 2.2.2. Typical 2-band Application for Europe Table 4 and Figure 2 show the band and resistor value details for a typical European 2-band application. Table 4. Typical European 2-Band Selection Band Number Band Name Band Frequency Range De-emphasis Stereo LED on Threshold (Only for Si483x-B) Total R to GND (k, 1%) Band2 FM1 87–108 MHz 50 µs Separation = 12 dB, RSSI = 28 57 Band22 AM2 522–1620 kHz 257 Figure 2. Typical 2-Band Selection Circuit for Europe Rev. 0.2 7 AN555 2.2.3. Typical 2-band application for US Table 5 and Figure 3 show the band and resistor value details for a typical 2-band application for the U.S. Table 5. Typical U.S. 2-Band Selection Band Number Band Name Band Frequency Range De-emphasis Stereo LED on Threshold (Only for Si483x-B) Total R to GND (k, 1%) Band4 FM1 87–108 MHz 75 µs Separation = 12 dB, RSSI = 28 77 Band21 AM1 520–1710 kHz 247 Figure 3. Typical 2-Band Selection Circuit for US 8 Rev. 0.2 AN555 3. Si483x-B/Si4820/24 SSOP Schematic and Layout This section shows the typical schematic and layout required for optimal Si483x-B/Si4820/24 performance. There are basically two working modes for the Si483x-B: “Volume” and “Bass/Treble” modes. Adding a pull-up resistor of 10 k on pin2 STATION sets the chip in "Volume" mode and removing the pull-up resistor sets the chip in "Bass/Treble" mode, as illustrated in Figure 4. When working in Bass/Treble mode, the Bass/Treble can be controlled via two push buttons with eight levels or by a slide switch with two or three levels. When working in “Volume” mode, tuner audio output volume can be adjusted with 2 push buttons in 32 steps (2 dB per step). Additionally, the default power up volume level can be set with pull-up/down resistors. Compared with the Si483xB, Si4820/24 only works in “Volume” mode, not “Bass/Treble” mode. The following sections describe in detail the applications circuits for different working modes. Figure 4. Si483x-B Mode Selection Rev. 0.2 9 AN555 3.1. Si483x-B/Si4820/24 Basic Volume Mode Applications Circuits Figure 5 and Figure 6 illustrate the basic applications circuits for typical 4-band FM/AM radios if using Si4831-B/ Si4820 or 12-band FM/AM/SW radios if using Si4835-B/Si4824. The chip works in "Volume" mode without internal volume adjustment. Volume control can be performed at audio amplifier circuit stage. For Si483x-B, the pull-up resistor R42 of 10K for pin 2 STATION is a must for this application. C6 and C15 are required bypass capacitors for VDD1/VDD2 power supply pin 20/21. Place C6/C15 as close as possible to the VDD1/VDD2 pin 20/21 and DBYP pin 22. These recommendations are made to reduce the size of the current loop created by the bypass cap and routing, minimize bypass cap impedance and return all currents to the DBYP pin. Pin 22 is the dedicated bypass capacitor pin. Do not connect it to power supply GND on PCB. Pin 13 and pin 14 are the GND of the chip, these pins must be well connected to the power supply GND on PCB. Pin 9 is the RFGND of the chip, it must be well connected to the power supply GND on PCB. When doing PCB layout, try to create a large GND plane underneath and around the chip. Route all GND (including RFGND) pins to the GND plane. C4 and/or C7 (4.7uF) are ac coupling caps for receiver analog audio output from pin 23 and/or pin 24. The input resistance of the amplifier R, such as a headphone amplifier, and the capacitor C will set the high pass pole given by Equation 1. Placement location is not critical. 1 f c = ---------------2RC Equation 1. C2 and C3 (22 pF) are crystal loading caps required only when using the internal oscillator feature. Refer to the crystal data sheet for the proper load capacitance and be certain to account for parasitic capacitance. Place caps C2 and C3 such that they share a common GND connection and the current loop area of the crystal and loading caps is minimized. Y1 (32.768 kHz) is an optional crystal required only when using the internal oscillator feature. Place the crystal Y1 as close to XTALO pin 18 and XTALI pin 19 as possible to minimize current loops. If applying an external clock (32.768 kHz) to XTALI, leave XTALO floating. Do not route digital signals or reference clock traces near pin 6 and 7. Do not route Pin 6 and 7. These pins must be left floating to guarantee proper operation. Pin 16, 17 are volume control or bass/treble control pins for using tuner internal volume control function or bass/ treble control function. In this basic application circuit, the tuner internal volume control function is not used, just connect the two pins to GND. VR1 (100K / 10%), R27, C1, C13 constitute the tuning circuit. 10 k at 10% tolerance is recommended for VR1. 1P12T switch S2 together with resistor ladder constitute band select circuits. Si4831/Si4820 includes all AM and FM bands as defined in above section 2.1, Si4835/Si4824 includes all AM, FM and SW bands. Q1(2SC9018) together with it’s peripherals B6, C30,31,33,36, R31,32,34,41 is the LNA circuit for all SW bands, the LNA is switched off by LNA_EN signal in AM and FM mode controlled by Si4835/Si4824. For Si4820/24, do not route pin 23. This pin must be left floating to guarantee proper operation. 10 Rev. 0.2 5 N Q & 5 N )RU6LRQO\ N0 % /1$B(1 >@ & Q 5 5 5 N 4 6& 9&& S & X & & X Rev. 0.2 N 5 & S Q+ / & X )0, & 5 5 X X & 95 N %$1' >@ )06: 9&& $0, *1' 1& *1' 1& 567 5)*1' 92/75(%/( 1& ;7$/ 92/%$66 1& ;7$/, %$1' < X & X & RSWLRQDO & S .+] 9'' 781( 9'' 781( '%<3 67(5(2 67$7,21 5287 & S /287 6L[% 8 X & X & ' 6WHUHRLQGLFDWRU ' 7XQLQJLQGLFDWRU >@ 781( >@ /1$B(1 5 5 5 5 N 5 9&& 9&& 5287 /287 9&& $17 %$1' >@ )RU6LRQO\ 6 781( >@ 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N )00+]0+] )00+]0+] )00+]0+] $0N+]N+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] AN555 Figure 5. Si483x-B Basic Volume Mode Applications Circuit 11 9&& $17 0:IHUULWHDQWHQQD AN555 TUNE1 [1] R36 33k 1% R43 30k 1% ANT2 SW8 (21.2MHz - 22MHz) [1] TUNE1 FM/SW VR1 50k 10% C1 47u 0.1u R35 20k 1% For Si4824 only C13 VCC R27 C36 0.47u 100R R32 10R C34 33p [1] BAND 1 2 NC TUNE1 LNA_EN 3 5 6 7 8 9 4 TUNE2 BAND NC NC FMI 10 11 S2 BAND [1] NC DBYP VDD2 AOUT 24 23 22 21 VDD1 20 XTALI 19 VOL- VOL+ RST XTAL0 18 17 16 14 13 Si482x-A C4 For Si4824 only 4.7u VCC R6 100k C6 C15 0.1u 4u7 AOUT 1 SW4(11.45MHz - 12.25MHz) 2 3 4 5 6 7 8 9 10 11 12 13 R11 20k 1% SW3(9.2MHz - 10.0MHz) R14 20k 1% SW2(6.8MHz - 7.6MHz) R9 20k 1% VCC C19 0.1u R12 20k 1% [1] LNA_EN RFGND NC NC AMI SW5 (13.4MHz - 14.2MHz) U1 GND R34 100k Q1 2SC9018 0.47u 15 33n 10p GND 2.5k/100M C5 ANT1 MW ferrite antenna R41 120k C30 B6 C33 12 270nH R31 1k [1] SW6 (15MHz - 15.9MHz) R10 20k 1% L2 C31 33n LNA_EN SW7 (17.1MHz - 18MHz) R15 20k 1% SW1 (5.6MHz - 6.4MHz) R8 50k 1% Y1 AM1 (520kHz - 1710kHz) R7 32.768KHz C2 22p 20k 1% C3 22p FM3 (64MHz - 87MHz) R28 40k 1% optional FM2 (76MHz - 90MHz) R29 120k 1% FM1 (87MHz - 108MHz) R33 20k 1% R44 47k 1% Figure 6. Si4820/24 Basic Volume Mode Applications Circuit 12 Rev. 0.2 Rev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i483x-B Applications Circuits with 9-level Bass/Treble Control via 2 Push Buttons Figure 7 sets Si483x-B in Bass/Treble mode by removing the pull-up resistor of pin 2 STATION. Pushing button S3 once increases bass effect by one level, and pushing button S4 once increases treble effect by one level. By pressing and holding one of the buttons, the bass or treble effect will automatically step through all levels until reaching their maximums. There are nine levels for bass/treble control. Figure 7. Si483x-B Applications Circuit with 9-Level Bass/Treble Control 13 9&& 6 5 N Q & 5 N 5 5 )RU6LRQO\ N0 % /1$B(1 >@ & Q S & Rev. 0.2 6 EDVV $17 0:IHUULWHDQWHQQD WUHEOH QRUPDO 4 6& 5 N X & & X 5 5 N N & S Q+ / & X 5 N 5 5 X X 95 N & & X & RSWLRQDO & S .+] < X & 1& %$1' >@ 9&& 9&& 67(5(2 )06: 9&& $0, *1' 1& *1' 1& 567 5)*1' 92/75(%/( )0, 92/%$66 ;7$/ 1& ;7$/, %$1' 9'' 781( 9'' 781( '%<3 67$7,21 5287 & S /287 14 6L[% 8 X & X & ' 6WHUHRLQGLFDWRU ' 7XQLQJLQGLFDWRU >@ 781( >@ /1$B(1 5 5 5 5 9&& 5287 /287 9&& $17 %$1' >@ )RU6LRQO\ 6 781( >@ Figure 8. Si483x-B 3-Level Bass/Treble Mode Applications Circuits 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N )00+]0+] )00+]0+] )00+]0+] $0N+]N+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] AN555 3.3. Si483x-B Applications Circuits with 3-level Bass/Treble Control via Slide Switch Figure 8 sets Si483x-B in Bass/Treble mode by removing the pull-up resistor of pin 2 STATION. Slide switch S5 controls bass/treble effect in three levels, bass/normal/treble. 9&& Rev. 0.2 5 N 5 N Q & 5 N 9&& )RU6LRQO\ N0 % & Q 5 S & 5 1& 9&& 5 1& 4 6& 5 N 9&& 5 N 5 6 /1$B(1 >@ 5 5 5 1& 9&& 5 1& X & X & 5 N & S Q+ / 1& 9&& YROXPH )0, 5 5 X X 95 N & & X & RSWLRQDO & S .+] < X & %$1' >@ & X 6 $17 0:IHUULWHDQWHQQD YROXPH 67(5(2 )06: 9&& $0, *1' 1& *1' 567 5)*1' 92/75(%/( 92/%$66 1& ;7$/ 1& ;7$/, %$1' 9'' 781( 9'' 781( '%<3 67$7,21 5287 & S /287 6L[% 8 X & >@ /1$B(1 5 5 5 N 5 5 X & ' 6WHUHRLQGLFDWRU ' 7XQLQJLQGLFDWRU >@ 781( 9&& 9&& 5287 /287 9&& $17 %$1' >@ )RU6LRQO\ 6 781( >@ 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N )00+]0+] )00+]0+] )00+]0+] $0N+]N+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] AN555 3.4. Si48x-B/Si4820/24 Application Circuits with 32-Level Volume Control via 2 Push Buttons Figure 9 sets Si483x-B in "Volume" mode by adding the pull-up resistor R42 of 10K at pin 2 STATION. Figure 10 illustrates the application circuit for Si4820/24. Pressing button S3 once decreases the volume level by 2 dB; pressing button S4 once increases the volume level by 2 dB. A total of 32 steps (2 dB per step) are available for the push button volume control. If pressing and holding S3 or S4, tuner volume will step through all levels until reaching the minimum or maximum, respectively. Figure 9. Si483x-B Applications Circuits with 32-Level Volume Control 15 9&& AN555 TUNE1 [1] R36 33k 1% R43 30k 1% ANT2 SW8 (21.2MHz - 22MHz) [1] TUNE1 FM/SW VR1 50k 10% C1 47u 0.1u For Si4824 only C13 R35 20k 1% VCC R27 C36 0.47u 100R R32 10R C34 33p [1] BAND 1 2 NC TUNE1 LNA_EN 3 5 6 7 8 9 4 TUNE2 BAND NC NC FMI 11 10 NC RFGND S2 BAND [1] AOUT NC DBYP VDD2 Si482x-A 24 23 22 21 VDD1 20 XTAL0 VOL- RST XTALI 19 18 17 14 13 VOL+ U1 GND R34 100k SW5 (13.4MHz - 14.2MHz) C4 For Si4824 only 4.7u VCC VCC VCC R6 100k C6 C15 0.1u 4u7 AOUT 1 SW4(11.45MHz - 12.25MHz) 2 3 4 5 6 7 8 9 10 11 12 13 R11 20k 1% SW3(9.2MHz - 10.0MHz) R14 20k 1% SW2(6.8MHz - 7.6MHz) R9 20k 1% VCC C19 0.1u R12 20k 1% [1] LNA_EN 16 Q1 2SC9018 NC AMI 0.47u GND 33n 10p 15 2.5k/100M C5 ANT1 MW ferrite antenna R41 120k C30 B6 C33 12 270nH R31 1k [1] SW6 (15MHz - 15.9MHz) R10 20k 1% L2 C31 33n LNA_EN SW7 (17.1MHz - 18MHz) R15 20k 1% SW1 (5.6MHz - 6.4MHz) R8 S4 volume+ S3 volume- 50k 1% Y1 AM1 (520kHz - 1710kHz) R7 32.768KHz C2 22p 20k 1% C3 22p FM3 (64MHz - 87MHz) R28 40k 1% R37 56k R38 56k optional FM2 (76MHz - 90MHz) R29 120k 1% FM1 (87MHz - 108MHz) R33 20k 1% R44 47k 1% Figure 10. Si4820/24 Applications Circuit with 32-Level Volume Control At the device power up, Si483x-B/Si4820/24 will put the output volume at some default levels according to the push button configurations as shown in Figure 11. There are four default volume level choices. Adding pull-down resistors to both pin 16 and 17 sets the default volume to maximum, typically 80 mVrms for FM and 60 mVrms for AM. Different pin 16 and 17 pull-up/down resistor combinations can set the default volume to either Max, Max-6dB, Max-12dB or Max-18dB. For example, in Figure 9, two pull-up resistors are connected to pin 16 and pin 17, which sets the default volume to Max-18dB. 16 Rev. 0.2 AN555 Figure 11. Si483x-B/Si4820/24 Default Volume Selection in Volume Mode 3.5. Application Circuits for Memorization of User Settings Si483x-B/Si4820/24 has high retention memory (HRM) built-in that can memorize the last volume and bass/treble settings so that at the next power up, the unit will automatically restore the volume and bass/treble settings before the last power off. The unit requires pin 20 Vdd1 to be connected to an always-on power source such as battery terminals. During power off/on cycling, there is a low probability that the user setting data in HRM can be corrupted by transient. If the tuner finds that the stored data in HRM is corrupted at power on, it will switch to use the default volume or bass/treble setting. To safeguard the integrity of HRM data, users are advised to ensure that the Reset pin (RSTB) voltage goes down to 0.3*VDD before the VDD2 voltage drops to 1.65 V during the power off process. A 2P2T, power on/off switch S3 in Figure 12 is recommended, with one pole of S3 short pin15 RSTB to GND immediately at the power off event. Applying always-on power supply voltage to Vdd1 and using 2P2T power on/off switch to connect RSTB will also improve the tuned channel consistency before power off and after power on. Si483x-B/Si4820/24 memorizes the last tuned station before power off and restores the original tuned station at power up after confirming that there is not a large enough position change on PVR during the power off/on cycle. Rev. 0.2 17 5 N 5 N Q & )RU6LRQO\ N0 % /1$B(1 >@ & Q & X 5 5 S & 4 6& 5 N 5 N 9&& 5 N $17 0:IHUULWHDQWHQQD 6 X & & X 567 >@ / Q+ N 5 & S )0, Rev. 0.2 RSWLRQDO & S .+] < 5 5 X X 95 N & & %$1' >@ 9&& 9&& $0, *1' 1& *1' 1& 567 5)*1' 92/75(%/( 1& ;7$/ 92/%$66 1& ;7$/, & X & X & S %$1' 9'' 781( 9'' 781( '%<3 67(5(2 67$7,21 5287 /287 X & 5 5 9%$7 6L[% 8 X X X9 & 9&& 6 5287 /287 & X >@ /1$B(1 5 5 5 N 5 5 567 >@ & & ' 6WHUHRLQGLFDWRU ' 7XQLQJLQGLFDWRU >@ 781( 9&& 9&& 9&& 18 9&& $17 9%$7 %$1' >@ )RU6LRQO\ 6 781( >@ 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N 5 N )00+]0+] )00+]0+] )00+]0+] $0N+]N+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] 6:0+]0+] AN555 Figure 12. Si483x-B Applications Circuits with User Setting Memory YROXPH YROXPH 6 AN555 3.6. Si483x-B/Si4820/24 Bill of Materials 3.6.1. Si483x-B/Si4820/24 Basic Volume Mode Applications Circuit BOM Table 6. Si483x-B Basic Volume Mode Applications Circuit BOM Component(s) Value/Description Supplier C4,C7,C15 Capacitor 4.7 µF, ±20%, Z5U/X7R Murata C13 Capacitor 47 µF, ±20%, Z5U/X7R Murata C1,C6,C19 Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R Murata C36 Supply bypass capacitor, 0.47 µF, ±20%, Z5U/X7R Murata C34 RF coupling capacitors, 33 pF, ±5%, COG Murata L2 Inductor 270 nH. Murata R5,R21 LED biasing resistors, 200 , ±5% Venkel VR1 Variable resistor (POT), 100 k, , ±10% Kennon D1,D3 Station and Stereo indicating LEDs Any, depends on customer U1 Si483xB AM/FM/SW Analog Tune Analog Display Radio Tuner Silicon Laboratories R6 Resistor, 100 k, ±5% Venkel R27 Resistor, 100 ,, ±5% Venkel R28 Band switching resistor, 40 k,, ±1% Venkel R44 Band switching resistor, 47 k,, ±1% Venkel R36 Band switching resistor, 33 k,, ±1% Venkel R43 Band switching resistor, 30 k,, ±1% Venkel R7,R33 Band switching resistor, 20 k,, ±1% Venkel R29 Band switching resistor, 120 k,, ±1% Venkel S2 Band switch Shengda C2, C3 Crystal load capacitors, 22 pF, ±5%, COG (Optional: for crystal oscillator option) Venkel Y1 32.768 kHz crystal (Optional: for crystal oscillator option) Epson ANT2 Whip antenna Various ANT1 MW ferrite antenna 220 µH Jiaxin Electronics Rev. 0.2 19 AN555 Table 7. Si4820/24 Basic Volume Mode Applications Circuit BOM Component(s) Supplier C4,C7,C15 Capacitor 4.7 µF, ±20%, Z5U/X7R Murata C13 Capacitor 4.7 µF, ±20%, Z5U/X7R Murata C1,C6,C19 Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R Murata C36 Supply bypass capacitor, 0.47 µF, ±20%, Z5U/X7R Murata C34 RF coupling capacitors, 33 pF, ±5%, COG Murata Inductor 270 nH Murata Variable resistor (POT), 100 k, ±10% Kennon L2 VR1 U1 Si4820/24 AM/FM/SW Analog Tune Analog Display Radio Tuner R6 Resistor, 100 k, ±5% Venkel R27 Resistor, 100 , ±5% Venkel R28 Band switching resistor, 40 k, ±1% Venkel R44 Band switching resistor, 47 k, ±1% Venkel R36 Band switching resistor, 33 k, ±1% Venkel R43 Band switching resistor, 30 k, ±1% Venkel R7,R33 Band switching resistor, 20 k, ±1% Venkel R29 Band switching resistor, 120 k, ±1% Venkel S2 C2, C3 Band switch Silicon Laboratories Shengda Crystal load capacitors, 22 pF, ±5%, COG (Optional: for crystal oscillator option) Venkel 32.768 kHz crystal (Optional: for crystal oscillator option) Epson ANT2 Whip antenna Various ANT1 MW ferrite antenna 220 µH. Y1 20 Value/Description Jiaxin Electronics Rev. 0.2 AN555 Table 8. Si4835-B/Si4824 Additional BOM (for 8 SW Bands) Component(s) Value/Description Supplier C36 Capacitor, 0.47 µF, ±20%, Z5U/X7R Murata C33 Capacitor capacitors, 10 pF, ±5%, COG Murata C30-31 Capacitor capacitors, 33 nF, ±5%, COG Murata B6 Ferrite bead,2.5k, 100 MHz Murata Q1 RF transistor, 2SC9018. ETC R34 Resistor, 100 k, ±5% Venkel R41 Resistor, 120 k, ±5% Venkel R32 Resistor, 10R, ±5% Venkel R31 Resistor, 1k,, ±5% Venkel R9-12,R14-15,R35 Band switching resistor, 20 k,, ±1% Venkel R8 Band switching resistor, 50 k, ±1% Venkel 3.6.2. Additional BOM for Applications Circuit with 9-level Bass/Treble Control via Push Buttons Table 9. Si483x-B Additional BOM for 9-Level Bass/Treble Control Component(s) Value/Description Supplier R1-2 Resistor, 56 k, ±5% Venkel S3-4 Button switch Various 3.6.3. Additional BOM for Application Circuit with 3-level Bass/Treble Control via Slide Switch Table 10. Si483x-B Additional BOM for 3-Level Bass/Treble Control Component(s) Value/Description Supplier R37-38 Resistor, 56 k, ±5% Venkel S5 Slide switch Shengda 3.6.4. Additional BOM for Application Circuit with 32-level Volume Control via Push Buttons Table 11. Si483x-B Additional BOM for 32-Level Volume Control Component(s) Value/Description Supplier R1-2 Resistor, 56 k, ±5% Venkel S3-4 Button switch Various Rev. 0.2 21 AN555 Table 12. Si4820/24 Addtional BOM for 32-Level Volume Control Component(s) Value/Description Supplier R37-38 Resistor, 56 k, ±5% Venkel S3-4 Button switch Various 3.6.5. Additional BOM for Application Circuit with Memorization of User Settings Table 13. Si483x-B Additional BOM for User Setting Memory 22 Component(s) Value/Description Component(s) R1-2 Resistor, 56 k, ±5% Venkel S3-4 Button switch Various S1 2P2T slide switch Shengda R16 Resistor, 200R, ±5% Venkel C40 Supply bypass electrolytic capacitor, 100 µF, 4 V Any C39 Supply bypass capacitor, 0.1 µF, ±20%, Z5U/X7R Murata Rev. 0.2 AN555 3.7. Si483x-B/Si4820/24 PCB Layout Guidelines 1-layer PCB is used for Si483x-B/Si4820/24 routed by large plane Power routed with traces 0402 component size or larger 10 mil traces width 20 mil trace spacing 15 mil component spacing Recommended to keep the AM ferrite loop antenna at least 5 cm away from the tuner chip Keep the AM ferrite loop antenna at least 5 cm away from MCU, audio AMP, and other circuits which have AM interference Place Vdd1/Vdd2 bypass capacitor C6, C15 as close as possible to the supply (pin 20/pin 21) and DBYP (pin 22). GND Do not connect the DBYP (pin 22) to the board GND. Place the crystal as close to XTALO (pin 18) and XTALI (pin 19) as possible. Route all GND (including RFGND) pins to the GND plane underneath the chip. Try to create a large GND plane underneath and around the chip. Do not route pin 6 and 7. These pins must be left floating to guarantee proper operation. Keep the Tune1 and Tune2 traces away from pin 6 and pin 7. Route Tune1 and Tune2 traces in parallel and the same way. Place C1, C13 as close to pin3 TUNE1 as possible. For Si4820/24, do not route pin 23, leave it floating to guarantee proper operation. Copy the Si483x-B layout example as much as possible when doing PCB layout. Figure 13. Si483x-B PCB Layout Example Rev. 0.2 23 AN555 4. Headphone Antenna for FM Receive The Si483x-B/Si4820/24 FM Receiver component supports a headphone antenna interface through the FMI pin. A headphone antenna with a length between 1.1 and 1.45 m suits the FM application very well because it is approximately half the FM wavelength (FM wavelength is ~3 m). 4.1. Headphone Antenna Design A typical headphone cable will contain three or more conductors. The left and right audio channels are driven by a headphone amplifier onto left and right audio conductors and the common audio conductor is used for the audio return path and FM antenna. Additional conductors may be used for microphone audio, switching, or other functions, and in some applications the FM antenna will be a separate conductor within the cable. A representation of a typical application is shown in Figure 14. Figure 14. Typical Headphone Antenna Application 24 Rev. 0.2 AN555 4.2. Headphone Antenna Schematic Figure 15. Headphone Antenna Schematic The headphone antenna implementation requires components LMATCH, C4, F1, and F2 for a minimal implementation. The ESD protection diodes and headphone amplifier components are system components that will be required for proper implementation of any tuner. Inductor LMATCH is selected to maximize the voltage gain across the FM band. LMATCH should be selected with a Q of 15 or greater at 100 MHz and minimal dc resistance. AC-coupling capacitor C4 is used to remove a dc offset on the FMI input. This capacitor must be chosen to be large enough to cause negligible loss with an LNA input capacitance of 4 to 6 pF. The recommended value is 100 pF to 1 nF. Ferrite beads F1 and F2 provide a low-impedance audio path and high-impedance RF path between the headphone amplifier and the headphone. Ferrite beads should be placed on each antenna conductor connected to nodes other than the FMIP such as left and right audio, microphone audio, switching, etc. In the example shown in Figure 15, these nodes are the left and right audio conductors. Ferrite beads should be 2.5 k or greater at 100 MHz, such as the Murata BLM18BD252SN1. High resistance at 100 MHz is desirable to maximize RSHUNT, and therefore, RP. Refer to “AN383: Si47xx Antenna, Schematic, Layout, and Design Guidelines,” Appendix A–FM Receive Headphone Antenna Interface Model for a complete description of RSHUNT, RP, etc. ESD diodes D1, D2, and D3 are recommended if design requirements exceed the ESD rating of the headphone amplifier and the Si483x-B/Si4820/24. Diodes should be chosen with no more than 1 pF parasitic capacitance, such as the California Micro Devices CM1210. Diode capacitance should be minimized to reduce CSHUNT and, therefore, CP. If D1 and D2 must be chosen with a capacitance greater than 1 pF, they should be placed between the ferrite beads F1 and F2 and the headphone amplifier to minimize CSHUNT. This placement will, however, reduce the effectiveness of the ESD protection devices. Diode D3 may not be relocated and must therefore have a capacitance less than 1 pF. Note that each diode package contains two devices to protect against positive and negative polarity ESD events. C9 and C10 are 125 uF ac coupling capacitors required when the audio amplifier does not have a common mode output voltage and the audio output is swinging above and below ground. Optional bleed resistors R5 and R6 may be desirable to discharge the ac-coupling capacitors when the headphone cable is removed. Rev. 0.2 25 AN555 Optional RF shunt capacitors C5 and C6 may be placed on the left and right audio traces at the headphone amplifier output to reduce the level of digital noise passed to the antenna. The recommended value is 100 pF or greater, however, the designer should confirm that the headphone amplifier is capable of driving the selected shunt capacitance. The schematic example in Figure 15 uses the National Semiconductor LM4910 headphone amplifier. Passive components R1 R4 and C7 C8 are required for the LM4910 headphone amplifier as described in the LM4910 data sheet. The gain of the right and left amplifiers is R3/R1 and R4/R2, respectively. These gains can be adjusted by changing the values of resistors R3 and R4. As a general guide, gain between 0.6 and 1.0 is recommended for the headphone amplifier, depending on the gain of the headphone elements. Capacitors C7 and C8 are ac-coupling capacitors required for the LM4910 interface. These capacitors, in conjunction with resistors R1 and R2, create a high-pass filter that sets the audio amplifier's lower frequency limit. The high-pass corner frequencies for the right and left amplifiers are: 1 1 f CRIGHT = ----------------------------------- f CLEFT = ----------------------------------2 R1 C7 2 R2 C8 Equation 2. With the specified BOM components, the corner frequency of the headphone amplifier is approximately 20 Hz. Capacitor C1 is the supply bypass capacitor for the audio amplifier. The LM4910 can also be shut down by applying a logic low voltage to the number 3 pin. The maximum logic low level is 0.4 V and the minimum logic high level is 1.5 V. The bill of materials for the typical application schematic shown in Figure 15 is provided in Table 14. Note that manufacturer is not critical for resistors and capacitors. 4.3. Headphone Antenna Bill of Materials Table 14. Headphone Antenna Bill of Materials 26 Designator Description LMATCH IND, 0603, SM, 270 nH, MURATA, LQW18ANR27J00D C4 AC coupling cap, SM, 0402, X7R, 100 pF D1, D2, D3 IC, SM, ESD DIODE, SOT23-3, California Micro Devices, CM1210-01ST U3 IC, SM, HEADPHONE AMP, National Semiconductor, LM4910MA R1, R2, R3, R4 RES, SM, 0603, 20 k C7, C8 CAP, SM, 0603, 0.39 UF, X7R C5, C6 CAP, SM, 0402, C0G, 100 pF R5, R6 RES, SM, 0603, 100 k F1, F2 FERRITE BEAD, SM, 0603, 2.5 k, Murata, BLM18BD252SN1D C1 CAP, SM, 0402, X7R, 0.1 µF R7 RES, SM, 0402, 10 k Rev. 0.2 AN555 4.4. Headphone Antenna Layout To minimize inductive and capacitive coupling, inductor LMATCH and headphone jack J24 should be placed together and as far from noise sources such as clocks and digital circuits as possible. LMATCH should be placed near the headphone connector to keep audio currents away from the chip. To minimize CSHUNT and CP, place ferrite beads F1 and F2 as close as possible to the headphone connector. To maximize ESD protection diode effectiveness, place diodes D1, D2, and D3 as close as possible to the headphone connector. If capacitance larger than 1 pF is required for D1 and D2, both components should be placed between FB1, FB2, and the headphone amplifier to minimize CSHUNT. Place the chip as close as possible to the headphone connector to minimize antenna trace capacitance, CPCBANT. Keep the trace length short and narrow and as far above the reference plane as possible, restrict the trace to a microstrip topology (trace routes on the top or bottom PCB layers only), minimize trace vias, and relieve ground fill on the trace layer. Note that minimizing capacitance has the effect of maximizing characteristic impedance. It is not necessary to design for 50 transmission lines. To reduce the level of digital noise passed to the antenna, RF shunt capacitors C5 and C6 may be placed on the left and right audio traces close to the headphone amplifier audio output pins. The recommended value is 100 pF or greater; however, the designer should confirm that the headphone amplifier is capable of driving the selected shunt capacitance. 4.5. Headphone Antenna Design Checklist Select an antenna length of 1.1 to 1.45 m. Select matching inductor LMATCH to maximize signal strength across the FM band. Select matching inductor LMATCH with a Q of 15 or greater at 100 MHz and minimal dc resistance. Place inductor LMATCH and headphone connector together and as far from potential noise sources as possible to reduce capacitive and inductive coupling. Place the chip close to the headphone connector to minimize antenna trace length. Minimizing trace length reduces CP and the possibility for inductive and capacitive coupling into the antenna by noise sources. This recommendation must be followed for optimal device performance. Select ferrite beads F1-F2 with 2.5 k or greater resistance at 100 MHz to maximize RSHUNT and, therefore, RP. Place ferrite beads F1-F2 close to the headphone connector. Select ESD diodes D1-D3 with minimum capacitance. Place ESD diodes D1-D3 as close as possible to the headphone connector for maximum effectiveness. Place optional RF shunt capacitors near the headphone amplifier’s left and right audio output pins to reduce the level of digital noise passed to the antenna. Rev. 0.2 27 AN555 5. Whip Antenna for FM Receiver A whip antenna is a typical monopole antenna. 5.1. FM Whip Antenna Design A whip antenna is a monopole antenna with a stiff but flexible wire mounted vertically with one end adjacent to the ground plane. There are various types of whip antennas including long, non-telescopic metal whip antennas, telescopic metal whip antennas, and rubber whip antennas. Figure 16 shows the telescopic whip antenna. Figure 16. Telescopic Whip Antennas The whip antenna is capacitive, and its output capacitance depends on the length of the antenna (maximum length ~56 cm). At 56 cm length, the capacitance of the whip antenna ranges from 18 to 32 pF for the US FM band. The antenna capacitance is about 22 pF in the center of the US FM band (98 MHz). 5.2. FM Whip Antenna Schematic Figure 17. FM Whip Antenna Schematic L1 (56 nH) is the matching inductor and it combines with the antenna impedance and the FMI impedance to resonate in the FM band. C5 (1nF) is the ac coupling cap going to the FMI pin. U3 is a required ESD diode since the antenna is exposed. The diode should be chosen with no more than 1 pF parasitic capacitance, such as the California Micro Device CM1213. 28 Rev. 0.2 AN555 5.3. FM Whip Antenna Bill of Materials Table 15. FM Whip Antenna Bill of Materials Designator Description WIP_ANTENNA Whip Antenna L1 Tuning Inductor, 0603, SM, 56 nH, MURATA, LQW18AN56nJ00D C5 AC coupling capacitor, 1 nF, 10%, COG U3 IC, SM, ESD DIODE, SOT23-3, California Micro Devices, CM1213-01ST 5.4. FM Whip Antenna Layout Place the chip as close as possible to the whip antenna. This will minimize the trace length between the device and whip antenna, which will minimize parasitic capacitance and the possibility of noise coupling. Place inductor L1 and the antenna connector together and as far from potential noise sources as possible. Place the ac coupling capacitor, C5, as close to the FMI pin as possible. Place ESD diode U3 as close as possible to the whip antenna input connector for maximum effectiveness. 5.5. FM Whip Antenna Design Checklist Maximize whip antenna length for optimal performance. Select matching inductor L1 with a Q of 15 or greater at 100 MHz and minimal dc resistance. Select L1 inductor value to maximize resonance gain from FM frequency (64 MHz) to FM frequency (109 MHz) Place L1 and whip antenna close together and as far from potential noise sources as possible to reduce capacitive and inductive coupling. Place the chip as close as possible to the whip antenna to minimize the antenna trace length. This reduces parasitic capacitance and hence reduces coupling into the antenna by noise sources. This recommendation must be followed for optimal device performance. Place ESD U3 as close as possible to the whip antenna for maximum effectiveness. Select ESD diode U3 with minimum capacitance. Place the ac coupling capacitor, C5, as close to the FMI pin as possible. Rev. 0.2 29 AN555 6. Ferrite Loop Antenna for AM Receive Two types of antenna will work well for an AM receiver: a ferrite loop antenna or an air loop antenna. A ferrite loop antenna can be placed internally on the device or connected externally to the device with a wire connection. When the ferrite loop antenna is placed internally on the device, it is more susceptible to picking up any noise within the device. When the ferrite loop antenna is placed outside a device, e.g., at the end of an extension cable, it is less prone to device noise activity and may result in better AM reception. 6.1. Ferrite Loop Antenna Design The following figure shows an example of ferrite loop antennas. The left figure is the standard size ferrite loop antenna, which is usually used in products with a lot of space, such as desktop radios. The right figure is the miniature size of the loop antenna compared with a U.S. 10-cent piece (dime). It is usually used in small products where space is at a premium, such as cell phones. If possible, use the standard size ferrite loop antenna as it has a better sensitivity than the miniature one. Figure 18. Standard and Miniature Ferrite Loop Antennas A loop antenna with a ferrite inside should be designed such that the inductance of the ferrite loop is between 180 and 450 uH for the Si483x-B/Si4820/24 AM Receiver. Table 16 lists the recommended ferrite loop antenna for the Si483x-B/Si4820/24 AM Receiver. Table 16. Recommended Ferrite Loop Antenna Part # Diameter Length Turns Ui Type Application SL8X50MW70T 8 mm 50 mm 70 400 Mn-Zn Desktop Radios SL4X30MW100T 4 mm 30 mm 100 300 Ni-Zn Portable Radios (MP3, Cell, GPS) SL3X30MW105T 3 mm 30 mm 105 300 Ni-Zn SL3X25MW100T 3 mm 25 mm 110 300 Ni-An SL5X7X100MW70T 5x7 mm 100 mm 70 400 Mn-Zn The following is the vendor information for the ferrite loop antennas: Jiaxin Electronics Shenzhen Sales Office email: [email protected] Web: www.firstantenna.com 30 Rev. 0.2 Desktop Radios AN555 6.2. Ferrite Loop Antenna Schematic Figure 19. AM Ferrite Loop Antenna Schematic C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 µF. D1 is an optional ESD diode if there is an exposed pad going to the AMI pin. 6.3. Ferrite Loop Antenna Bill of Materials Table 17. Ferrite Loop Antenna Bill of Materials Designator Description ANT1 Ferrite loop antenna, 180–450 H C1 AC coupling capacitor, 0.47 µF, 10%, Z5U/X7R D1* ESD diode, IC, SM, SOT23-3, California Micro Devices, CM1213-01ST *Note: Optional; only needed if there is any exposed pad going to the AMI pin. 6.4. Ferrite Loop Antenna Layout Place the chip as close as possible to the ferrite loop antenna feedline. This will minimize the trace going to the ferrite antenna, which will minimize parasitic capacitance as well as the possibility of noise sources coupling to the trace. The placement of the AM antenna is critical because AM is susceptible to noise sources causing interference in the AM band. Noise sources can come from clock signals, switching power supply, and digital activities (e.g., MCU). When the AM input is interfaced to a ferrite loop stick antenna, the placement of the ferrite loop stick antenna is critical to minimize inductive coupling. Place the ferrite loop stick antenna as far away from interference sources as possible. In particular, make sure the ferrite loop stick antenna is away from signals on the PCB and away from even the I/O signals of the chip. Do not route any signal under or near the ferrite loop stick. Route digital traces in between ground plane for best performance. If that is not possible, route digital traces on the opposite side of the chip. This will minimize capacitive coupling between the plane(s) and the antenna. To tune correctly, the total capacitance seen at the AMI input needs to be minimized and kept under a certain value. The total acceptable capacitance depends on the inductance seen by the chip at its AM input. The acceptable capacitance at the AM input can be calculated using the formula shown in Equation 3. Rev. 0.2 31 AN555 1 C Total = ------------------------------------------------2 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 29 pF when a 300 uH ferrite loop stick antenna is used for an AM band with 10 kHz spacing, where the highest frequency in the band is 1750 kHz. 6.5. Ferrite Loop Antenna Design Checklist Place the chip as close as possible to the ferrite loop antenna feedline to minimize parasitic capacitance and the possibility of noise coupling. Place the ferrite loop stick antenna away from any sources of interference and even away from the I/O signals of the chip. Make sure that the AM antenna is as far away as possible from circuits that switch at a rate which falls in the AM band (504–1750 kHz). Recommend keeping the AM ferrite loop antenna at least 5 cm away from the tuner chip. Place optional component D1 if the antenna is exposed. Select ESD diode D1 with minimum capacitance. Do Not Place any ground plane under the ferrite loop stick antenna if the ferrite loop stick antenna is mounted on the PCB. The recommended ground separation is 1/4 inch or the width of the ferrite. Route traces from the ferrite loop stick connectors to the AMI input via the ac coupling cap C1 such that the capacitance from the traces and the pads is minimized. 32 Rev. 0.2 AN555 7. Air Loop Antenna for AM An air loop antenna is an external AM antenna (because of its large size) typically found on home audio equipment. An air loop antenna is placed external to the product enclosure making it more immune to system noise sources. It also will have a better sensitivity compared to a ferrite loop antenna. 7.1. Air Loop Antenna Design Figure 20 shows an example of an air loop antenna. Figure 20. Air Loop Antenna Unlike a ferrite loop, an air loop antenna will have a smaller equivalent inductance because of the absence of ferrite material. A typical inductance is on the order of 10 to 20 uH. Therefore, in order to interface with the air loop antenna properly, a transformer is required to raise the inductance into the 180 to 450 uH range. T1 is the transformer to raise the inductance to within 180 to 450 uH range. A simple formula to use is as follows: Typically a transformer with a turn ratio of 1:5 to 1:7 is good for an air loop antenna of 10 to 20 uH to bring the inductance within the 180 to 450 uH range. Choose a high-Q transformer with a coupling coefficient as close to 1 as possible and use a multiple strands Litz wire for the transformer winding to reduce the skin effect. All of this will ensure that the transformer will be a low loss transformer. Finally, consider using a shielded enclosure to house the transformer or using a torroidal shape core to prevent noise pickup from interfering sources. A few recommended transformers are listed in Table 18. Rev. 0.2 33 AN555 Table 18. Recommended Transformers Transformer 1 Transformer 2 Transformer 3 Vendor Jiaxin Electronics UMEC UMEC Part Number SL9x5x4MWTF1 TG-UTB01527S TG-UTB01526 Surface Mount Surface Mount Through Hole Primary Coil Turns (L1) 12T 10T 10T Secondary Coil Turns (L2) 70T 55T 58T ULSA / 0.07 mm x 3 n/a n/a Type Wire Gauge Inductance (L2) 380 µH ±10% @ 796 kHz Q 184 µH min, 245 µH typ @ 179 µH min, 263 µH typ @ 100 kHz 100 kHz 130 50 The following is the vendor information for the above transformer: Vendor #1: Jiaxin Electronics Shenzhen Sales Office email: [email protected] Web: www.firstantenna.com Vendor #2: UMEC USA, Inc. Website: www.umec-usa.com www.umec.com.tw 34 Rev. 0.2 75 AN555 7.2. Air Loop Antenna Schematic Figure 21. AM Air Loop Antenna Schematic C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 uF. D1 is a required ESD diode since the antenna is exposed. 7.3. Air Loop Antenna Bill of Materials Table 19. Air Loop Antenna Bill of Materials Designator Description LOOP_ANTENNA Air loop antenna T1 Transformer, 1:6 turns ratio C1 AC coupling capacitor, 0.47 µF, 10%, Z5U/X7R D1 ESD diode, IC, SM, SOT23-3, California Micro Devices, CM1213-01ST 7.4. Air Loop Antenna Layout Place the chip and the transformer as close as possible to the air loop antenna feedline. This will minimize the trace going to the air loop antenna, which will minimize parasitic capacitance and the possibility of noise coupling. When an air loop antenna with a transformer is used with the Si483x-B/Si4820/24, minimize inductive coupling by making sure that the transformer is placed away from all sources of interference. Keep the transformer away from signals on the PCB and away from even the I/O signals of the Si483x-B/Si4820/24. Do not route any signals under or near the transformer. Use a shielded transformer if possible. 7.5. Air Loop Antenna Design Checklist Select a shielded transformer or a torroidal shape transformer to prevent noise pickup from interfering sources Select a high-Q transformer with coupling coefficient as close to 1 as possible Use multiple strands Litz wire for the transformer winding Place the transformer away from any sources of interference and even away from the I/O signals of the chip. Make sure that the AM antenna is as far away as possible from circuits that switch at a rate which falls in the AM band (504–1750 kHz). Route traces from the transformer to the AMI input via the ac coupling cap C1 such that the capacitance from the traces and the pads is minimized. Select ESD diode D1 with minimum capacitance. Rev. 0.2 35 AN555 8. Whip Antenna for SW Receiver SW reception usually uses whip antennas, the same as FM. 8.1. SW Whip Antenna Design A whip antenna is a monopole antenna with a stiff but flexible wire mounted vertically with one end adjacent to the ground plane. There are various types of whip antennas, including long non-telescopic metal whip antennas, telescopic metal whip antennas, and rubber whip antennas. Figure 22 shows the telescopic whip antenna. Figure 22. Telescopic Whip Antenna for SW 8.2. SW Whip Antenna Schematic Figure 23. SW Whip Antenna Schematic Q1 2SC9018 is a low noise RF transistor and it constitutes a LNA to amplify the SW signal coming from the whip antenna. C30 (33nF) is the ac couplijng cap between whip antenna and LNA input. C33 (0.47uF) is the ac coupling cap going to the AMI pin. R31, R41 are bias resistors of the transistor. 36 Rev. 0.2 AN555 8.3. SW Whip Antenna Bill of Materials Table 20. SW Whip Antenna Bill of Materials Designator Description WHIP_ANTENNA Whip Antenna Q1 Low noise RF transistor, 2SC9018 C30 AC coupling capacitor, 33 nF, 10%, COG C33 Coupling capacitor, 0.47 µF, ±20%, Z5U/X7R R31 Resistor, 1 k, ±5% R41 Resistor, 200 k, ±5% 8.4. SW Whip Antenna Layout Place the chip and 2SC9018 as close as possible to the whip antenna feedline. This will minimize the trace going to the whip antenna, which will minimize parasitic capacitance as well as the possibility of noise sources coupling to the trace. 8.5. SW Whip Antenna Design Checklist Maximize whip antenna length for optimal performance. Q1 and whip antenna close together and as far from potential noise sources as possible to reduce capacitive and inductive coupling. Place the chip as close as possible to the whip antenna to minimize the antenna trace length. This reduces parasitic capacitance and hence reduces coupling into the antenna by noise sources. This recommendation must be followed for optimal device performance. Place the ac coupling capacitor C33, as close to the AMI pin as possible. Place Rev. 0.2 37 AN555 CONTACT INFORMATION Silicon Laboratories Inc. 400 West Cesar Chavez Austin, TX 78701 Tel: 1+(512) 416-8500 Fax: 1+(512) 416-9669 Toll Free: 1+(877) 444-3032 Please visit the Silicon Labs Technical Support web page: https://www.silabs.com/support/pages/contacttechnicalsupport.aspx and register to submit a technical support request. The information in this document is believed to be accurate in all respects at the time of publication but is subject to change without notice. Silicon Laboratories assumes no responsibility for errors and omissions, and disclaims responsibility for any consequences resulting from the use of information included herein. Additionally, Silicon Laboratories assumes no responsibility for the functioning of undescribed features or parameters. Silicon Laboratories reserves the right to make changes without further notice. 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Other products or brandnames mentioned herein are trademarks or registered trademarks of their respective holders. 38 Rev. 0.2