2.3.3. FAQ On Hardware Design
1. Typical phenomenon: The current ripple is not large, but the TX performance of RF is rather
bad.
Problem description: ripple has a strong impact on the performance of RF TX. It should be noted
that ripple must be tested when ESP8266EX sends normal packets. The ripple increases when the
power gets high. Generally, the ripple value should <120mV when sending the packet 11N MCS7the
ripple value should <200mV when sending the packet 11B 11M.
Solution: add a10uF filter capacitor to the branch of source circuit ( ESP8266EX AVDD pin). 10uF
capacitor should be placed adjacent to the VDDA pin. The ripple is much small and more stable
when it’s near the pin.
2. Typical phenomenon: when the chipset is sending data packages, the power ripple is small
and the TX performance of the RF is not good
Problem description: the poor TX performance of the RF is not only caused by the problematic
power ripple, but also by abnormal crystal, for example, the crystal itself is of low quality and the
crystal frequency offset is too big (when over ±40PPM, the ESP8266EX will not be able to work
properly and the performance will get worse accordingly); or the crystal has been interfered with
high frequency signals, for example, the input signals couple with the output signals or the output
signals couple with the input signals due to the cross wiring of input and output signal wires at
different layers; or high frequency signal wires are wired below the crystal such as the SDIO wiring
and UART wiring, which will cause malfunction of the crystal. Another problem that has not received
due attention is the existence of inductive or radioactive parts beside the crystal, for example, great
inductance, antenna (many designers, when considering the area of the ESP8266EX module, often
place the crystal very close to the PCB on-board antenna, which, at the time ESP8266EX module
sends data packages, will lead to direct coupling between radioactive interference and the crystal,
the crystal and the antenna, thus resulting in very poor performance of the RF).
Solution: this problem is mainly caused by inconsiderate layout and can only be solved by re-layout.
See Chapter 2.7.2 for details about layout.
3. Typical phenomenon: when ESP8266EX is sending data packages, the power value tested
by an instrument is much higher or lower than the target power value, and the EVM is
relatively poor
Problem description: the sharp difference between the power value tested by an instrument and the
target power value is largely caused by the mismatch of the resistance in the section from the chipset
RF pin to the antenna. That is to say the resistance in the section from the chipset RF pin to the
antenna deviates from the 50Ω a lot, leading to reflections during signal transmission. The reflections
To Next Page
Loading...
