A switched-capacitor biquad using a simple quasi-unity gain amplifier

This paper presents a SC biquad using a simple quasi-unity gain amplifier. In sub-nanometer CMOS technologies the intrinsic gain of the transistors is low, this increases the difficulty of designing high gain amplifiers. The proposed SC filter is based on the Sallen-Key biquad and it requires only a simple low gain amplifier. A differential filter circuit, including a suitable low gain amplifier based on a fully-differential voltage-combiner is presented. The correct functionality of this circuit is validated through electrical simulations of a cascaded sixth order filter. These simulations show that for a clock frequency of 100 MHz, the frequency response of the circuit is very similar to the one of the prototype filter, with only a relative error of 1.1% in the attenuation value at the cutoff frequency.