A Novel Direct Injection-Locked QPSK Modulator Based on Ring VCO in 180 nm CMOS

A novel quadrature phase-shift keying (QPSK) modulator that employs injection locking for the phase modulation as well as the phase-locked clock generation is presented. By using the proposed simple modulator based on a ring voltage-controlled oscillator (VCO), many blocks in the conventional QPSK modulators are removed, and the total area can be reduced.The proposed QPSK modulator was fabricated in a 180 nm CMOS, and occupies an area of 0.024 mm² . The modulator achieves measured error vector magnitude (EVM) of 8.23% at 50.8 Mb/s under QPSK modulation with the total power consumption of lower than 6 mW from a 1.8 V power supply.