This paper proposes the use of sampled-data operation in op-amps. The technique favors very low supply voltage and micro-power. After discussing the method at a general level, a possible sampled-data scheme is analyzed. Simulations with a low threshold technology show that a 0.5-V supply is possible. A version of the circuit, which has been integrated by using a standard 0.18-mu m CMOS technology (with high thresholds), is able to operate at 0.65-V supply voltage. Simulation results show 42.5 dB of DC gain and 2.5-kHz bandwidth with 0.5-pF load capacitor. The power consumption is 63 nW. A pseudo-differential scheme doubles the consumed power and increases the DC gain by 6 dB.