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Rev. 0.3 2/13 Copyright © 2013 by Silicon Laboratories AN602 AN602 Si4822/26/27/40/44 A NTENNA , S CHEMATIC , L AYOUT , AND D ESIGN G UIDELINES 1. Introduction This document provides general Si48 22/26/27/40/44 design and AM/FM/SW antenna selection guidelines, including schematic, BOM, and PCB layout. All users s hould follow the Si4822/26/27/40/44 design guidelines presented in “2. Si4822/26/27/40/44 Default Frequency Band Definition and Selection”and “3. Si48422/26/27/40/44 SSOP/SOIC Schematic and Layout” and choose the appropriate antennas based on the applications and device used as described in “4. Headphone Antenna for FM Receive” through “8. Whip Antenna for SW Receiver”. Table 1. Part Selection Guide
Description
Si4822 Entry level wheel-tuned digital display AM/FM Receiver, Mono audio Si4826 Entry level wheel-tuned digital display AM/FM/SW Receiver, Mono audio Si4827 Entry level wheel-tuned digital display AM/FM/SW Receiver, wide FM/SW band, Mono audio Si4840 Wheel-tuned digital display AM/FM Receiver, Stereo audio Si4844 Wheel-tuned digital display AM/FM/ SW Receiver, wide FM/SW band, Ste- reo audio
- Si4822/26/27/40/44 Default Frequency Band Definition and Selection
selections, which results in a total 41 combinations to choose from. to the frequency range desired. Table 2. Band Sequence Definition
Table 2. Band Sequence Definition (Continued)
Some commonly used bands and their respective selection circuits are listed below for your quick reference. Figure 1 and Table 3 illustrate the band and resistor value details for a typical 12-band application.
Figure 1. A Typical 12-Band Selection Circuit
Figure 2 and Table 4 show the band and resistor value details for a typical European 2-band application. Table 3. Typical 12-Band Selection Table 4. Typical European 2-Band Selection
8 Rev. 0.3 3. Si48422/26/27/40/44 SSOP/SOIC Schematic and Layout This section shows the typical schematic and layout required for optimal Si4822/26/27/40/44 performance. Si4822/ 26/40/44 offer two methods to select the radio band by tuner setting and two methods to set band property by tuner setting. Normally, there are four kinds of typical application circuits in real application, however, the Si4827 offers two methods to select the radio band by tuner setting and two methods to set band property by host MCU, so there are two kinds of typical application circuits in real application. 3.1. Si4822/26/40/44 Application Circuit: Host MCU Select Radio Band and Set Band Property Figure 4 shows the applications circuits of Si4822/26/40/44 when the application is to us e the host MCU to select radio band and set band property. Normally, a push button for selecting band is connected to the host MCU. The MCU then detects the push button’s action and sends a command to Si4822/26/40/44 to set the desired band. The host MCU can also set the band property, such as band top frequency point and bottom frequency point, stereo indication threshold (only for Si4840/ 44), de-emphasis, AM tuning spacing, etc. The two key points to ensure Si4822/26/40/44 works properly are as follows: 1. No pull-up resistor is connected to pin 1 LNA_EN 2. Pin 5 BAND is connected to its power supply V CC directly C6 & C15 are required bypass capacitors for V DD1/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. C4 and/or C7 (4.7 µF) 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 capaci tance, C, will set the high pass pole given by Equation 1. Placement locations of C4 and C7 are not critical. Equation 1. High-Pass Pole Calculation C28 and C29 (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 ce rtain to account for parasitic capacitance. Place caps C28 and C29 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 & 7. These pins must be left floating to guarantee proper operation. Pin 2, 15, 16, 17 are the required communi cation pins with host MCU. A 100 k pull-up resistor R6 and 0.1 µF bypass cap C19 are recommended for the pin 15 RST. Pull-up resistor R3 of 10 k is necessary for pin 16 SDIO. VR1 (100 k / 10%), R27, C1, C13 constitute the tuning circuit. 100kat 10% tolerance is recommended for VR1. Q1(2SC9018), together with its 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 Si4826/44. For Si4822/26, do not route pin 23. This pin must be left floating to guarantee proper operation. fc
Figure 4. Si4822/26/40/44 Applications Circuit: MCU Select Band and Set Band Property
14 GND
15 RST
16 SDIO
17 SCLK
18 XTALO
19 XTALI
20 VDD1
21 VDD2
22 DBYP
23 ROUT/NC
24 LOUT/AOUT
- Add pull-up resistor R42 of 10k to pin 1 LNA_EN.
- Ensure pin 5 BAND is connected to its power supply VCC directly.
Figure 5. SiSi4822/26/40/44 Applications Circuit: MCU Select Default Band and Use Default Band
- No pull-up resistor is connected to pin 1 LNA_EN.
- Pin 5 BAND is connected to slide switch.
Figure 6. Si4822/26/40/44 Applications Circuit: Slide Switch Select Band and
only define the band properties which are not fixed in the default band definition, such as softmute property, etc.
- Add pull-up resistor R42 of 10 k to pin 1 LNA_EN.
- Pin 5 BAND is connected to slide switch.
Figure 7. Si4822/26/40/44 Applications Circuit: Slide Switch Select Band and Use Default Band
Table 6. Si4822/26/40/44 Applications Circuit: Host MCU Select Band and Set Band Property
Table 7. Si4822/26/40/44 Applications Circuit: MCU Select Default Band and Use Default Band
Table 8. Si4822/26/40/44 Application Circuits: Slide Switch Select Band and MCU Re-define Band
Table 9. Si4822/26/40/44 Application Circuits: Slide Switch Select Band and Use Default Band
Table 10. Si4827 Application Circuit: MCU Select Band
Table 11. Si4827 Application Circuit: Slide Switch Select Band
Place VDD1/VDD2 bypass capacitor C6, C15 as close as possible to the supply (pin20/pin 21) and DBYP (pin 22). Do not connect the DBYP (pin 22) to the board GND. trace and XTALI trace as small as possible. underneath and around the chip. Do not route Pin 6 and 7. These pins must be left floating to guarantee proper operation. Place C1, C13 as close to pin3 TUNE1 as possible. For Si4822/26, do not route pin 23, leave it floating to guarantee proper operation. Try to refer to the Si4840/44 PCB Layout example as much as possible when doing Si4822/26/27 PCB layout. Figure 10. Si4840/44 PCB Layout Example
- Headphone Antenna for FM Receive
approximately half the FM wavelength (FM wavelength is ~3 m). of a typical application is shown in Figure 11. Figure 11. Typical Headphone Antenna Application
With the specified BOM components, the corner frequency of the headphone amplifier is approximately 20 Hz. manufacturer is not critical for resistors and capacitors. Table 12. Headphone Antenna Bill of Materials
26 Rev. 0.3 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 source s such as clocks and digital circuits as possible. L MATCH 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 effe ctiveness, 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 and FB2 and the headphone amplifier to minimize C SHUNT. Place the chip as close as possible to the headpho ne 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 ampl ifier 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.
input connector for maximum effectiveness. 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. capacitive and inductive coupling. 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. Table 13. FM Whip Antenna Bill of Materials
Figure 16. 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. Table 15. Ferrite Loop Antenna Bill of Materials exposed pad going to the AMI pin.
Rev. 0.3 31 6.4. Ferrite Loop Antenna Layout Place the chip as close as possible to the ferrite loop ant enna feedline. This will minimize the trace going to the ferrite antenna, which in tu rn will minimize parasitic capacitance and also will minimize the possibility of noise sources coupling to the trace. The placement of the AM antenna is critical, since AM is susceptible to noise sources causing interference in the AM band. Noise sources can come from clock signals, sw itching 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 th e ferrite loop stick antenn a is away from signals on the PCB and away from even the I/O signals of the chip. Do not route any signal u nder or near the ferrite loop stick. Route digital traces in between ground plane for best performance. If that is not po ssible, 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 2 Equation 2. Expected Total Capacitance at AMI Where: C Total = Total capacitance at the AMI input Leffective = Effective inductance at the AMI input fmax = Highest frequency in AM band 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 ca se 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 elem ents of the circuit into account. The input capacitance of the AMI input is 8 pF. The formula shown in Equation 2 gives a total capacitance of 28 pF when a 300 µH 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. Please 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). Keep the AM ferrite loop antenna at least 5 cm away from the tuner chip (recommended). 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. CTotal 2fmax 2Leffective
Table 16. Recommended Transformers
Figure 18. 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. or near the transformer. Use a shielded transformer if possible. the AM band (504 to 1750 kHz). from the traces and the pads is minimized. Select ESD diode D1 with minimum capacitance. Table 17. Air Loop Antenna Bill of Materials
sources coupling to the trace. Maximize whip antenna length for optimal performance. capacitive and inductive coupling. recommendation must be followed for optimal device performance. Place the ac coupling capacitor C33, as close to the AMI pin as possible. Table 18. SW Whip Antenna Bill of Materials
Rev. 0.3 37 DOCUMENT CHANGE LIST Revision 0.2 to Revision 0.3 Updated "1.Introduction" Updated "2.Si4822/26/27/40/44 Default Frequency Band Definition and Selection" Added "3.5 Si4827 application circuit: Host MCU select radio band" Added "3.6 Si4827 application circuit: Slide switch select radio band" Added "Table10.Si44827 application circuit: Host MCU select radio band" Added "Table11. Si4827 application circuit: Slide switch select radio band"
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