A 3 V pseudo-differential transconductor with intrinsic rejection of the common-mode input signal

Transconductance differential amplifiers directly referred to ground (we will call them “pseudo-differential” structures to distinguish from the fully-differential ones) are not intrinsically capable of rejecting the common-mode (CM) input signal. This paper deals with the problems related to the propagation of the CM signal in differential circuits. A new pseudo-differential transconductor architecture with a high Common-Mode Rejection Ratio (CMRR) is proposed. The novel structure is based on a transconductor sensible only to CM signals which is added in parallel to the original one, in order to implement a feed-forward cancellation of the CM output signal current. An efficient circuital implementation of this structure is presented. Comparative simulations demonstrate that the proposed technique is competitive with the classical fully-differential one particularly at high frequency when the CMRR rapidly degrades