Espressif Systems ESP32-C3 Series, Руководство по проектированию аппаратного обеспечения, Страница: 25 / 30

3 PCB Layout Design
3.8 Typical Layout Problems and Solutions
3.8.1 Ripple in the power supply is not large, but the RF transmit (TX) performance is
rather poor.
Analysis:
Ripple in the power supply can significantly affect the RF TX performance. Please note that ripple in the power
supply must be measured when ESP32-C3 family works in TX mode. Ripple in the power supply changes along
with power. The higher the power, the larger the ripple.
Generally, the peak value of the ripple should be < 80 mV when ESP32-C3 family transmits MCS7@11n packets,
and < 120 mV when ESP32-C3 family transmits 11m@11b packets.
Solution:
Add a 10 µ F filter capacitor to the branch of the power trace (the branch routed from the analog power supply
pin of ESP32-C3 family). The 10 µ F capacitor should be as close to the analog power supply pin as possible.
The closer the capacitor, the smaller the ripple.
3.8.2 Ripple in power supply is small during packet transmission, but RF TX perfor­
mance is still poor.
Analysis:
Besides ripple in the power supply, RF TX performance can also be affected by the crystal itself. The following
factors will result in poor RF performance:
• Large frequency deviation and other quality issues of the crystal
• Interference from high-frequency signals, e.g. signal coupling resulted from a cross-layer design
• High-frequency signal traces under the crystal, such as UART trace
• Inductive or radiation components around the crystal, such as inductors and entennas
Solution:
This problem is caused by improper PCB layout and can be solved by optimizing the layout. For layout principles,
please see Section 3 .
3.8.3 When ESP32­C3 family transmits data packets, the measured power is much
higher or lower than the target power, and the EVM is relatively poor.
Analysis:
The difference between the measured power and the target power may be due to signal reflection caused by the
impedance mismatch on the transmission line connecting the RF pin and the antenna. Besides, the impedance
mismatch will affect the working state of the internal PA, making the PA prematurely access the saturated region
in an abnormal way. The EVM becomes poor as the signal distortion happens.
Solution:
Match the antenna’s impedance with the reserved π circuit on the RF trace, so that impedance of the antenna as
seen from the RF pin matches closely with that of the chip. This will reduce reflection to the minimum.
3.8.4 TX performance is not bad, but the RX sensitivity is low.
Analysis:
As TX and RX share the antenna path, good TX performance indicates proper RF impedance matching. The
reason of low RX sensitivity might lie in coupling of high-frequency interference signals to the antenna. In this
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ESP32-C3 Family Hardware Design Guidelines V1.0