A sampled-data switched-current analog 16-tap FIR filter with digitally programmable coefficients in 0.8 μm CMOS

Abstract

A prototype 16-tap filter is designed. Target specifications are 7 b of linearity at 20 MSample/s with a signal bandwidth from DC to 10 MHz. Such a filter is applicable to 64-QAM digital modems over coaxial cable or twisted-pairs. The filter is implemented using switched currents. A single transconductor acts as the front-end interface circuit and converts an analog differential input voltage signal to a differential current. The signal current is sampled and held by class-AB current copier cells. The sampled current signals, unlike conventional CCD FIR filters, are held within the current copier cells and are not propagated through the taps. The robust digital coefficients are propagated, instead of the sensitive analog signals. Hence, the loss of signal fidelity is determined solely by leakage of the copier cells rather than the propagation loss. The filter, implemented in 0.8 /spl mu/m CMOS, is fully-programmable and can be configured to perform lowpass or bandpass functions respectively.