True-differential/common-mode mixed-mode S-parameter measurement techniques for cellular and 4G bandwidths

This paper introduces true-differential/common-mode mixed-mode S-parameter measurement techniques for cellular and 4G bandwidths. The on-chip differential amplifier is designed in a 130-nm RFCMOS process, where the simulated differential mode S-parameters are also presented over the wide frequencies (0.5 ~ 3.5 GHz) which includes cellular frequencies. The differential gains are 8.4 dB and 7.9 dB at 1 GHz and 3 GHz, respectively. The non-linear effects of the RF circuits can result in mixed-mode S-parameter measurement errors in virtual differential mode. Because real differential and common mode input signals stimulate a DUT in true differential mode, true differential/common mode measurements may reduce the measurement errors caused by the non-linear effects. Differential/common mixed-mode S-parameter tests were performed using an AD8350 IC from 0.1 GHz to 2.0 GHz. The various comparisons of measured input P1dB compression points and common mode rejection ratio (CMRRs) in true and virtual differential modes are presented.