1. Power (power supply to related devices): Filter capacitor is close to the pin of the related device.
Filter capacitance: between the positive and negative electrodes of the DC power supply, used to filter out AC, so that the direct flow is smooth.
The longer the wire, the larger the resistance, inductance, and the capacitance, which is not conducive to the delivery of the power supply, so the shorter the wire, the better,
The thicker, the filter capacitor is close to the chip, and the interference can be easily filtered, and it will be subject to secondary interference if it is too far.
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2. Power (power supply to related devices): The order of the filter capacitance is close to the chip.
If the small capacitance is far away, since there is an inductor and resistance, the high-frequency signal will be filtered, the effect is not good, that is, it is wrong. Therefore, small capacitors must be placed close to the IC pin.
Large filter low frequency, small filter high frequency
Because the large electrolysis is a rolled long aluminum foil, the self-inductance is large, high frequency impedance is very;
And small, it is much smaller inductance, so it can live too high;
3. Pa, 2G_PA Power above the 0603 package 22UF large capacitance. (Remark 10UF)
In the Buzz6T 4G GoPhone project, the location is reserved, but is not used, NC.
(Power supply to PA) PA power
PA is relatively high for power supply, plus this large capacitor is to improve the performance of the power supply. The large capacitance is filtered off the 217 Hz power ripple generated by the PA to keep the power supply voltage of the PA stabilizes. Otherwise, the power of the output changes, causing power of power.
Considering 1: Rong value is generally more, this large capacitor is Bulk Capacitor, is not a high frequency capacitor, theoretically, the smaller the PA power ripple. GSM PA is enough for dozens of uf. It can generally use more 6.3V / 22UF.
If you consider cost, you can almost. This capacitor is large, and it is generally not placed in the radio shield. Placed near the battery point of contact.
Nowadays, new PAs are now a 10uf power supply, which can take care of TX spurious performance, but close to the power connector or 22uf, the TAN capacitance is required to prevent current from the BB or other circuits.
Considering 2: Big pressure, higher than the voltage of the battery, generally withstand voltage. 1882. = 6.3V.
Consider 3: Material. Ceramics or tantalum capacitors can be. The cost is first.
Consider 4: Note ESR Must Low Enough. 1881.150U is better
This capacitor has a big impact on the linearity of the amplifier. Take the CDMA PA. If there is no such capacitor, the ACPR should be bad. This capacitance value is usually UF, because the low frequency filter, like CDMA, neighbor, neighboring spacing ( Offset frequency). 1881.1MHz, this capacitor impedance is small enough to 1MHz. Other modulations, the same considerations. The pressure should be satisfied at the same time to meet the RF voltage (Voltage Swing).
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4.WTR4905 (PDET): If WiFi 5G, TX_FBRX plus LPF filter is supported by 5G interference PDET, closed loop power control (calibration) Connector and Transceiver's RF line.
TX SAW: WTR4905 can not use TX SAW. If you need to use, TX Filter is placed in the PA shield.
The TX SAW action is to filter out the extra noise of the PA output. BUZZ6TEVDO schematic, B4, BC0, BC1 have not made
TX SAW is used with TX SAW, B13.
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5.TX: All DA outputs have internal flow bias, and the DC Blocking capacitors are needed outside. Also direct capacitor.
DC offset refers to the DC component in AC.
DA (Driver amplifier)
6. Match the device to place
The duplexer's own matching circuit is close to the duplex.
Receive matches close to Transceiver Pin.
PA output matches close to the output key.
My thinking (not necessarily accurate): 50 ohm characteristic impedance transmission line has a comprehensive advantage of transmitting energy density and efficiency.
Generally, the PCB panel will take a 50ohm trace, if you need to match, the port is not 50 ohm at the port of the device itself, and the 50oHM can reduce the reflection of the radio frequency transmission hour wave.
7. Temperature test is placed
RF temperature detecting thermistors near PA.
Crystal's temperature detection is close to Crystal.
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8. Receive the placement of SAW
Single SAW is close to receiving, such as Transceiver, WiFi.
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9. Keep away from the heat source (PA)
PA, WiFi chip cannot overlap, with PMIC and CPU chip distances of 6mm or more.
Crystal and TCXO are as far away from the heat source.
RF (including Transceiver and Wireless Chips, including Transceiver and Wireless Chips) on the back side of the double-sided device.
10.gps
Elna is close to the antenna.
Before SAW is placed near ELNA.
After SAW (if any) is close to the GPS receiving chip.
ELNA and before SAW are best masked separately.
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Class system NF:
Add ELNA (External LNA), one: Reduces F1, and dilute the effect of ELNA backend Noise figure on sensitivity. To reduce the NOISE Figure of the receiving path to improve the sensitivity. The INSERT LOSS of LNA and antenna to the LNA path is more important, so Elna should be placed close to the antenna.
Playing SAW: If the external noise is too large, the LNA / receiving chip is saturated, resulting in a decline in Gain, the stronger the strength of its noise, the more Gain drops. Use SAW to filter out noise, protect ELNA and receive chips. (You can refer to the relevant documentation)
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11. Travel
The layout line should ensure the shortest high frequency trace, the order is high and low frequency segment, and the path LOSS is reduced.
The same traces, Cable lines, low-frequency LOSS compared to high-frequency LOSS.
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12. Shield
Backlight circuit is separately masked.
The RF section requires two shield cover:
Devices such as TX Filters, PAS, Duplexers, Antenna Switches, and their matching networks need to be placed in a separate shield cover.
WTR4905, DRX SAWS, switch switch is put in a separate shield cover.
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13.EMI
EMI Filter and filter capacitors are placed near LCD, Camera, and TP.
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