Typical Layout Problems And Solutions; Q: The Current Ripple Is Not Large, But The Tx Performance Of Rf Is Rather Poor - Espressif Systems ESP32 Hardware Design Manuallines

2. SCHEMATIC CHECKLIST AND PCB LAYOUT DESIGN
and an increased number of high-frequency signals. We use the mainboard of a PAD or TV Box as an example
here to provide guidelines for the PCB layout and 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 with regards to the PCB design.
• As can be seen in Figure 19, ESP32 should be placed near the edge of the PCB and away from the CPU
and DDR, the main high-frequency noise sources. The distance between the chip and the noise sources
decreases the interference and reduces the coupled noise.
• It is suggested that a series resistor be reserved on the six signal traces when ESP32 communicates with
the CPU via SDIO to decrease the drive current and any interference, and also to eliminate the sequencing
problem caused by the inconsistent length of the SDIO traces.
• On-board PCB 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 associated memory should be routed strictly ac-
cording 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 parallel data or address buses.
• 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.

2.2.3 Typical Layout Problems and Solutions

2.2.3.1 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.
Generally, the peak-to-peak value of the ripple should be <80 mV when ESP32 sends MCS7@11n packets, and
<120 mV when ESP32 sends 11b/11m packets.
Espressif Systems
Figure 19: PAD/TV Box Layout
21 ESP32 Hardware Design Guidelines V2.1