A minimal integral nonlinearity criterion to optimize the design of a new tanh/sinh-type bipolar transconductor

We report on the use of a simple design optimization criterion for obtaining maximum static transfer function linearity. It is based on an analytic function that corresponds to the integral nonlinearity of the circuit. The criterion may be useful, either as an analytic tool to gain insight into the circuit´s behavior, or as an efficient computational alternative to calculating total harmonic distortion (THD). It is utilized here to optimize the design parameters of a recently proposed bipolar transconductor capable of high linearity, which is composed of two parallel-connected nonlinear blocks: a hyperbolic tangent-type transconductor and hyperbolic sine-type transconductor. Examination of this tanh/sinh-type transconductor concept, using the analytic version of the present criterion, indicates that this new circuit configuration is theoretically capable of achieving values of THD lower than possible with conventional bipolar hyperbolic tangent-type transconductors. A particular design example is presented to demonstrate, through simulations, the performance of the new transconductor, and in order to ascertain the ability of the proposed design optimization criterion for obtaining maximum static transfer function linearity. In this particular example, THD values of less than 0.3% are obtained with a 100-μS transconductance up to a maximum input voltage swing of 50-mV peak.