A Low-Power Baseband Filter Based on a 1.2-V 65-nm CMOS Bulk-Driven Linear Tunable Transconductor

A fourth-order Butterworth G(m)-C low-pass filter based on a low-voltage tunable CMOS transconductor using a bulk-driven gain-enhancement scheme is presented. This scheme uses a local feedback auxiliary amplifier to increase the effective gain of the cascode transistors and linearize the drain voltage of the input transistors biased in the triode region. The auxiliary amplifier uses the bulk terminals as inputs and its biasing current allows tuning the transconductance. The transconductor has been designed in a 65-nm CMOS technology with a 1.2 V supply voltage. As an application, a 1 MHz low-pass filter has been designed and fabricated in the same technology. The measured total harmonic distortion of the filter for a 300 mVpp output signal of 100 kHz is -43 dB. The filter occupies 0.15 mm(2) and consumes a power of 1.5 mW. Tuning capabilities are also shown.