Espressif Systems ESP32-S3 - RF; RF Circuit; RF Tuning

Chapter 3. Schematic Checklist
Fig. 8: ESP32-S3 Schematic for 32.768 kHz Crystal
Fig. 9: ESP32-S3 Schematic for External Oscillator
External signal Amplitude (Vpp, unit: V)
Sine wave or square wave 0.6 < Vpp < VDD
3.5 RF
3.5.1 RF Circuit
ESP32-S3’s RF circuit is mainly composed of three parts, the RF traces on the PCB board, the chip matching
circuit, the antenna and the antenna matching circuit. Each part should meet the following requirements:
• For the RF traces on the PCB board, 50 Ω impedance control is required.
• For the chip matching circuit, it must be placed close to the chip. A CLC structure is preferred.
– The CLC structure is mainly used to adjust the impedance point and suppress harmonics, and
a set of LC can be added if space permits.
– The RF matching circuit is shown in Figure ESP32-S3 Schematic for RF Matching.
• For the antenna and the antenna matching circuit, to ensure radiation performance, the antenna’s characteristic
impedance must be around 50 Ω. Adding a CLC matching circuit near the antenna is recommended to adjust
the antenna. However, if the available space is limited and the antenna impedance point can be guaranteed to
be 50 Ω by simulation, then there is no need to add a matching circuit near the antenna.
3.5.2 RF Tuning
The RF matching parameters vary with the board, so the ones used in Espressif modules could not be applied directly.
Follow the instructions below to do RF tuning.
Figure ESP32-S3 RF Tuning Diagram shows the general process of RF tuning.
In the matching circuit, de󰝘ne the port near the chip as Port 1 and the port near the antenna as Port 2. S11 describes
the ratio of the signal power re󰝙ected back from Port 1 to the input signal power, and S21 is used to describe the
transmission loss of signal from Port 1 to Port 2. If S11 is less than or equal to -10 dB and S21 is less than or equal to
-35 dB when transmitting 4.8 GHz and 7.2 GHz signals, the matching circuit can satisfy transmission requirements.
Espressif Systems 16
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