A linear, fully balanced, voltage-tunable CMOS operational transconductance amplifier (OTA) with large dc gain and wide bandwidth is described. The approach uses a twodifferential-pair transconductor with a cross-coupled input stage together with a negative resistance load for compensating the parasitic output resistance of the OTA. Since no additional internal nodes are generated, dc gain enhancement is obtained without bandwidth limitation. SPICE simulations show that total harmonic distortion at 1.42 V p -p is less than 1% with dynamic range equal to 66 dB at a power consumption of 2.7 mW from a single 5-V supply. As an example, the OTA is used to design a third-order elliptic lowpass filter in the very-high-frequency range, simulated in a standard 2 m CMOS process (MOSIS).The cutoff frequency of the filter is tunable in the range of 12-50 MHz.

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A general topology for transconductance‐capacitor (Gm‐C) filters is presented that permits any continuous‐time analog Gm‐C filter to be analysed via a matrix‐description. Based on these matrices, explicit formulas are derived for the transfer function and the sensitivities valid for any Gm‐C filter topology. The approach leads to a useful relationship between the passive capacitor network of the filter and the degree of its transfer function. The matrix‐based approach is formulated especially for efficient use in computer‐aided analysis and design of Gm‐C filters, but ‘hand designs’ of Gm‐C IFLF and LF filters are given as illustrative examples. A new, more general definition of Gm‐C state‐space filters is proposed. Connections between the state matrices for voltage‐ and current‐mode state‐space Gm‐C filters are formulated and two canonical transformations are defined that convert state‐space filters into direct state‐space ones, i.e. those having only grounded capacitors. Copyright © 2003 John Wiley & Sons, Ltd.

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