Mixer-first FSK receiver with automatic frequency control for body area networks

We present a low-power (382 mu W) body area network receiver operating in the 900 MHz band. The wideband FSK receiver supports bit rates up to 625 kbps. To save power, the power consuming phase-locked-loop (PLL) is replaced by an energy efficient digital automatic frequency control (AFC) loop. The AFC acts as a low-bandwidth frequency-locked-loop (FLL), using the FSK demodulator as frequency detector; the measured frequency offset is fed back to the on-chip digitally controlled oscillator. To further decrease the power consumption, the LNA is removed, the passive mixer being the first circuit in the receiver front-end. The mixer-first topology increases the linearity compared to injection-locked and envelope detector based receivers. Additionally, analytical passive mixer transducer power gain and noise figure models are presented which are used to obtain an optimal mixer-first design. We achieve a -81 dBm sensitivity at a bit rate of 12.5 kbps