A high order continuous-time Sigma-Delta Modulator (.SIGMA..DELTA.M) is
used for its high carrier-to-noise ratio (CNR) performance and low power
consumption. The modulator is designed to allow zero-IF, wide-band
low-pass or low-IF flexibility. The sigma-delta ADC modulator includes a
receiving circuit, a plurality of loop filter transconductors, a
plurality of feedforward weighting amplifiers, a first adding element, at
least a local feedback circuit, a quantizer, and a feedback DAC. The
local feedback circuit includes a feedback weighting amplifier and a
second adding element. The feedback coefficient of the feedback weighting
amplifier is tunable, and the local feedback circuits can be designed to
maximize bandwidth combination.