A delta-sigma modulator for a 1-bit digital switching amplifier

A seventh-order single-loop single-bit delta-sigma modulator for a 1-bit digital audio switching amplifier is presented. To achieve high SNR and ensure the modulator stability for a large input range, the positions of the modulator loop filter poles and zeros are optimized, and a feedback comparator is used. A test chip was fabricated in a 0.35-μm CMOS process with optional 5-V transistors. The modulator achieves an SNR of 111 dB and 0.0015-% THD+N over the audio band. The normalized maximum allowable input range is 0.89. There are two modulators on one chip, one for each left and right audio channel. The isolation between both channels is over 135 dB. The chip area is 12.6 mm² and it draws 60 mA from a 5-V supply.