A low-distortion digitally programmable continuous-time filter and variable-gain amplifier

A technique for low-distortion and digitally programmable continuous-time filtering is proposed. Digital controllability is based on an inherent linear MOST-only current division technique. This technique is applied to achieve a VGA with gain from -10 dB to 53 dB in steps of 1 dB and with linearity better than -80 dB. The filter is a 5th order Butterworth low-pass with ± 50% tuning range around 1.1 MHz. Dynamic range and linearity around -70 dB is achieved. The system has been fabricated in a low-cost 0.8 µm CMOS process. The chip consumes 34 mA from a 3.3 V supply.