A 6th-order continuous-time bandpass /spl Sigma//spl Delta/ modulator for digital radio IF

A bandpass SD Modulator (SDM) ADC uses negative feedback of a bandpass-filtered error-signal and a high oversampling ratio to reduce the in-band errors of a low-resolution quantizer. As high-order (>4) bandpass SDMs exhibit signal-dependent stability, multibit quantizers are often used to lower the quantization noise of a 2nd or 4th order SDM. However, the accuracy required of the intermediate quantizer levels is high as mismatch affects the overall SDM performance. A 6th-order SDM has a single-bit quantizer for digitizing IF signals of 10.7 MHz.