Mixer-First FSK Receiver With Automatic Frequency Control for Body Area Networks

We present a low-power (382
$\mu {\rm W}$
) 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
$-81~{\rm dBm}$
sensitivity at a bit rate of 12.5 kbps.