A 3.4-mW 54.24-Mbps burst-mode injection-locked CMOS FSK transmitter

A burst-mode frequency-shift keying (FSK) transmitter is presented using injection locking technique for wireless neural signal recording. An initial single current pulse is injected to the LC tank to start up the oscillator quickly and, more importantly, to set the phase of the free-running oscillation at known value. We prove that the free-running oscillation phase is linearly related to the logarithm of the initial current pulse magnitude. With the free-running oscillation phase fixed, a gated reference signal can be injected at the optimum timing to achieve fast settling and consequently realize the high-data-rate burst-mode FSK transmission. The duty cycle of the reference signal is controlled to be 33% to reduce the required reference signal power by 73% approximately. With burst-mode operation and direct modulation by changing the self-resonance frequency of the oscillator, low power consumption and high energy efficiency is achieved. The transmitter is implemented in a 0.18-μm CMOS technology. It achieves a maximum data rate of 54.24 Mbps while consuming 3.4 mW from a 1.8-V supply, resulting in the high energy efficiency of 62 pJ/bit.