A 1 V 2.5 μW fully-differential ASK demodulator with 12.5 pJ/bit FOM for ultra-low power biomedical applications

Wireless transceivers that receive data and power are important circuit blocks in implantable biomedical devices. In such wirelessly powered devices, supply and common-mode variations increase the error rate of the received data. In this paper we propose a fully-differential amplitude-shift-keying (ASK) demodulator for suppressing the effect of such undesired common mode variations on the received data. The proposed demodulator consists of a fully-differential envelope detector (ED) and programmable gain amplifier (PGA) that operates in the sub-threshold region, and a differential comparator that consumes only dynamic current. The proposed system is implemented in a 0.18 μm CMOS process and consumes 2.5 μA from a 1 V power supply. At a data rate of 200 kbps, this leads to an FOM of 12.5 pJ/bit.