A new OTA-C universal biquad resonates out the main parasitic capacitance

This paper proposes a core structure that provides, with minimum of adjustments, a wide range of second-order transfer functions, from the usual low-pass and band-pass to transfer functions with imaginary and complex zeroes. This universal biquad is implemented with transconductors and grounded capacitors. The performances of similar structures reported in the literature are significantly degraded by the parasitic capacitances present at their internal modes, especially those nodes without a placed capacitance. The biquad proposed here provides a way of resonating out the main parasitic capacitance, pushing most of its effects out of the band of interest. A design example demonstrates that this structure is suitable for the implementation of integrated filters operating in the tens of MHz frequency range.