Esp32 As A Slave Device; Typical Layout Problems And Solutions; Q: The Current Ripple Is Not Large, But The Tx Performance Of Rf Is Rather Poor - Espressif Systems ESP32 Series Manual

3.2 PCB Layout

3.2.2 ESP32 as a Slave Device

When ESP32 works as a slave device, the user needs to pay more attention to signal integrity in the PCB design. It
is important to keep ESP32 away from the interferences caused by the complexity of the system and an increased
number of high-frequency signals. We use the mainboard of a PAD or TV Box as an example here to provide
guidance on the PCB design.
The digital signals between the CPU and DDR are the main producers of the high-frequency noise that interferes
with Wi-Fi radio. Therefore, the following should be noted during the PCB design.
• As can be seen in Figure 15, ESP32 should be placed at the edge of the PCB and away from the CPU
and DDR, the main noise sources. The distance between the chip and the noise sources decreases the
interference and reduces the coupling noise.
• It is suggested that a 200Ω series resistor is added to the six signal traces when ESP32 communicates with
the CPU via SDIO to decrease the drive current and any interferences, and also to eliminate the sequence
problem caused by the inconsistent length of the SDIO traces.
• A PCB on-board antenna is not recommended, as it receives much interference and coupling noise, both of
which impact the RF performance. We suggest that you use an external antenna which should be directed
away from the PCB board via a cable, in order to weaken the high frequency interference with Wi-Fi.
• The high-frequency signal traces between the CPU and MEM should be routed strictly according to the
routing guidelines (please refer to the DDR trace routing guidelines). We recommend that you add ground
vias around the CLK traces separately, and around the data, or that you add traces in groups.
• The GND of the Wi-Fi circuit and that of other high-power devices should be separated and connected
through wires if there are high-power components, such as motors, in the design.
• The antenna should be kept away from high-frequency noise sources, such as LCD, HDMI, Camera Sensor,
USB, etc.

3.2.3 Typical Layout Problems and Solutions

3.2.3.1 Q: The current ripple is not large, but the Tx performance of RF is rather poor.

Analysis:
The current ripple has a strong impact on the RF Tx performance. It should be noted that the ripple must be
tested when ESP32 is in the normal working mode. The ripple increases when the power gets high in a different
mode.
Espressif Systems
Figure 15: PAD/TV Box Layout
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3 SCHEMATICS AND PCB LAYOUT DESIGN
ESP32 Hardware Design Guideline V1.0