Linearity guidelines for gm-C biquad filter design using architecture optimization with Volterra analysis

In analog design, a good understanding of nonlinear behavior is crucial and should be taken into account early in the design flow at the architectural level. This paper presents the design towards optimal linearity of a biquadratic section of a gm-C low-pass filter based on Nauta's transconductor. First, Volterra analysis is extended from circuit to architectural level by means of macro models. At circuit level, Volterra is used to optimize and size the transconductor while at architectural level, Volterra series define the main nonlinearity contributors of the biquad and hence allow to set the optimal filter parameters. These results are then translated into a design rule for optimal linearity in the full bandwidth at architectural level. Finally, a bottom-up verification is performed using circuit simulations to confirm the optimum. Both methods are applied on a 10 MHz Butterworth filter, designed in 0.13 mum CMOS. It achieves a SFDR of 67 dB and consumes 3 mW from a 1.2 V supply.