Low-distortion continuous-time integrated filters for low frequency applications

A technique for designing high-linearity continuous-time integrated filters for low frequency applications using transconductance network is presented. With this technique, an area-efficient transconductance network is used to replace the large resistors in low-frequency integrator-based continuous-time filters. The key challenge with this technique is in determining and realizing the appropriate relationship between the transconductance circuit and the nonideal frequency-dependent properties of the opamp. Simulation results for a third-order Bessel low-pass filter designed in a 0.5μm CMOS process with a cutoff frequency of 5 kHz provide a THD in excess of 70 dB for a 2V p-p output with the 5 V power supply.