A 900mV single-stage class-AB amplifier suitable for the Switched-Opamp technique is presented. To improve the slew-limited characteristics, a Dynamic Current Source (DCS) circuit which boosts the tail currents of the amplifier is proposed. The tail current of the proposed circuit is well defined and independent of technology parameters and supply variations. The tail current of the amplifier is 40µA with zero differential voltages, while the maximum output current is nearly 900µA. A single-loop 3rd order Σ-Δ modulator with the proposed amplifier was designed. For a 260mV 15.625kHz sinusoidal input signal, the simulated dynamic range of the modulator is 89dB.