To minimize the power consumption of an analog sigma-delta modulator (SDM), a fifth-order loop filter of the SDM has been realized with only three operational amplifiers (op-amp). The analog SDM with shared op-amp is applied to a class-D amplifier for a digital hearing aid. The class-D amplifier with the analog SDM has been realized in a standard 0.13-mu m CMOS process. The maximum output power level of the class-D amplifier is 1.13-mW for a load with 46.5-Omega DC resistance. The total harmonic distortion+noise (THD+N) and the dynamic range (DR) of the class-D amplifier are 0.0038-% and 96-dB, respectively. The fifth-order analog SDM with shared op-amp consumes only 0.2-mW from a 1.2-V power supply.