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

This paper discusses theoretically how impedance of peripheral circuits influences to the measurement of second-order inter-modulation distortion (IMD2) generated in radio frequency (RF) bulk acoustic wave (BAW) duplexers. First, IMD2 properties of RF BAW duplexers are expressed by a third-order tensor. A non-linear circuit model is applied, and basic properties of the tensor elements are discussed. Then the tensor expression is used to evaluate how the port termination affects the IMD2 output. It is shown that variation of IMD2 output causes mainly by following five mechanisms: (a) variation of the Tx signal intensity due to impedance mismatching at the Tx port, (a) variation of the jammer signal intensity due to impedance mismatching at the ANT port, (c) variation of detector read due to impedance mismatching at the Rx port, (d) reentry of the IMD2 signal to the ANT port due to impedance mismatching at the ANT port, and (e) reentry of the Tx signal to the ANT port due to impedance mismatching at the ANT port. Since input impedance of the ANT port is usually not defined for jammer signals, a large attenuator must be added to the ANT port for suppressing the impedance mismatching. This result is consistent with the experiments reported previously.