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.
Rezzi, F., Baschirotto, A., Castello, R. (1994). A 3 V pseudo-differential transconductor with intrinsic rejection of the common-mode input signal. In Proceedings of the 37th Midwest Symposium on Circuits and Systems (pp.85-88). Piscataway, NJ, United States : IEEE [10.1109/MWSCAS.1994.519196].
A 3 V pseudo-differential transconductor with intrinsic rejection of the common-mode input signal
BASCHIROTTO, ANDREA;
1994
Abstract
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.
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