A 124-GHz injection-locked quadrature voltage-controlled oscillator (ILQVCO) fabricated using a 40-nm CMOS process is presented. It locks onto a fundamental reference signal at 124 GHz generated on-chip from an external reference at 31 GHz, thereby avoiding generation of spurious noise commonly se en in the phase noise spectra of subharmonically injection-locked VCOs. The QVCO's phase noise levels in the free-running and injection-locked conditions are -87 dBc/Hz and -117 dBc/Hz, respectively, at 1-MHz offset. The high fundamental oscillation frequency and the low phase noise are realized by adopting a ring-type topology and transformers for inter-stage impedance matching. The ILQVCO is combined with an on-chip double-balanced quadrature modulator for vector signal generation. A 32QAM signal thus generated achieved a data rate of 25 Gb/s with an error-vector magnitude (EVM) of 5.1%.