Analysis of the common-mode induced differential-mode distortion in Gm-C filters

Effects of imbalance input on linearity of pseudodifferential ladder Gm‐C filters

“…are not dependent on V ic and therefore the 3rd-harmonic distortion component in the above equation is independent of V ic . This explains why the 3rd-harmonic distortion component in (21) is the same as the analytical result in [8] whereby the input voltages are assumed to be perfectly balanced, that is, V ic =0.…”

“…The analysis of in this section will be in analogous to the one in the previous section. In line with (6) and (8), by using state-space matrices defined in Appendix 2, the state vectors comprising linearised DM and CM node voltages in Fig. 4 can be found to be…”

“…respectively. It was shown in [8] that when the FD filter is driven by a pair of perfectly balance input voltages, that is, the cases where A = 1 and φ =0 ο , the DM output voltage of the filter will be composed of only the odd-harmonic components, that is…”

“…It was demonstrated in [8] that the cross-dependency between the DM and CM signals contributes significantly to the DM distortion in the FD filters. However, it is assumed in [8] that the input voltages of the FD filters are perfectly balanced. In reality this is not the case, for example, in practical receivers, imbalance can be introduced by non-ideality of circuits in the signal chain leading up the filter, notably the balun [9][10][11].…”

“…In general, this is not always true especially in the case where the FD transconductors with low CMR, for example, the ones with pseudodifferential structure, which are suitable for low‐voltage operation, are employed. It was demonstrated in [8] that the cross‐dependency between the DM and CM signals contributes significantly to the DM distortion in the FD filters. However, it is assumed in [8] that the input voltages of the FD filters are perfectly balanced.…”