A 1.2V direct background digital tuned continuous-time bandpass sigma-delta modulator

A 1.2 V continuous-time bandpass sigma-delta modulator implemented in a conventional 1.5 µm CMOS process is presented. Low supply voltage is achieved using biased inverting opamp configuration technique. The modulator is tuned using a direct background digital tuning technique, which measures the noise spectral densities of the modulator output digitally during normal operation and adjusts the tuning code according to the measured spectral densities. No extra ADC or DAC are required. For a sampling rate of 4 MHz, the maximum SNDR after tuning was measured to be 44.6 dB and the power dissipation was 2.1 mW.