A high speed CMOS amplifier with active feedforward compensation for contactless card reader

A high speed CMOS two stage amplifier with active feedforward compensation is designed for the 13.56MHz type B contactless card reader whose data rate is 847 kHz. A rail-to-rail input folded cascode amplifier is used as the first stage, a differential push-pull amplifier as the second stage, and a push-pull amplifier as the feedforward compensation stage. The active feedforward compensation shows better frequency character than the traditional compensation schemes, and the push-pull structure promotes the performance of amplifier. The amplifier was simulated in HHNEC 0.35μm CMOS digital process with single 3.3V power supply. The simulation results showed dc gain of around 93dB and phase margin of around 50 degree with high driven ability of a 20 PF capacitor. The gain bandwidth (GBW) is above 1GHz at the signal frequency 847 kHz, while its unit gain frequency is only 340MHz. This character is very useful to restrict the higher frequency carrier wave signal. It has been applied in the preamplifier, active RC filter and SC filter in our application.