A 5.9mW 50Mbps CMOS QPSK/O-QPSK transmitter employing injection locking for direct modulation

900MHz QPSK/O-QPSK transmitter suitable for biomedical high quality imaging application is presented. The phase modulation is achieved by directly modifying the self-resonant frequency of a sub-harmonic injection-locked oscillator through capacitor bank switching. Due to the simplicity of the proposed architecture, implemented in 0.18μm CMOS technology, it consumes very low power of 3mW and 5.88mW with 1.2V and 1.4V supply voltages respectively, while transmitting at 50Mbps data rate. The transmitter can deliver output power of -3.3dBm at 1.4V supply with an EVM of 6.6%.