In PCB circuit design, there are usually other analog circuits on board. For example, many circuits have analog to digital converter (ADC) or digital to analog converter (DAC). The high frequency signal emitted by the antenna of the RF transmitter may reach the analog input of ADC. Because any circuit may send or receive RF signals like an antenna. If the processing of the ADC input is not reasonable, the RF signal may be self excited in the ESD diode input by ADC, resulting in ADC bias.