  This paper presents an always-on low-power wake-up receiver (WuRx) that
activates the remainder of the system when a wake-up signal is detected. The
proposed receiver has two phases of waking up. The first phase uses an
integrated CMOS Schottky diodes to detect the signal power at a low bias
current. The approach dissipates low quiescent power and allows the reuse of
the design in multiple frequency bands with only modifying the matching
network. In the second phase, a data-locked startable oscillator is proposed to
correlate the received data with a target signature. This design eliminates the
area and power dissipation of an external crystal oscillator and only turns on
when the second phase is activated. By correlating to a target signature, the
second phase also reduces the probability of a false alarm (PFA) that would
otherwise wake up the high-power bulk of the system. The two-phase approach
leads to significant reduction in average power consumption when compared to a
single-phase design. This implementation targets sub-ms wake-up latency and
operates in the unlicensed band at a 750-MHz carrier frequency with a data rate
of 200 kbps. The design achieves $\sim$8.45pJ/bit and $<$-50 dBm of input
sensitivity and average power of 1.69$\mu$W. The system is implemented in 65-nm
CMOS technology and occupies an area of 1mm$\times$0.75mm.
