Theoretical considerations on influence of circuit impedance on IMD2 measurement of radio-frequency bulk acoustic wave duplexers

This paper discusses theoretically how the impedance of peripheral circuits influences the measurement of second-order inter-modulation distortion (IMD2) generated in RF BAW duplexers. First, IMD2 properties of RF BAW duplexers are expressed by a rank three tensor. Then, the tensor expression is used to evaluate how the port termination affects the IMD2 output. It is shown that variation of IMD2 output is caused mainly by five mechanisms: 1) variation of the transmit (Tx) signal intensity caused by impedance mismatching at the Tx port; 2) variation of the jammer signal intensity caused by impedance mismatching at the antenna (ANT) port; 3) variation of detector read caused by impedance mismatching at the receive (Rx) port; 4) reentry of the IMD2 signal to the ANT port caused by impedance mismatching at the ANT port; and 5) reentry of the Tx signal to the ANT port caused by impedance mismatching at the ANT port. Because input impedance of the ANT port is usually not defined for jammer signals, a large attenuator must be added to the ANT port to suppress the impedance mismatching. This result is consistent with experiments reported previously.