A 80–95 GHz direct quadrature modulator in SiGe technology

A direct carrier IQ modulator operating in the 80-95 GHz frequency range is presented. The circuit is designed and fabricated in 0.18μm SiGe technology with 170/250 GHz f_T/f_max. The modulator is based on double-balanced gilbert mixer cells with on-chip quadrature LO phase shifter and consumes 23mW DC power. In single-sideband operation, the chip exhibits up to 3 dB conversion gain below 85 GHz and -1± 0.5 dB up to 95 GHz. The image rejection ratio and LO-RF isolation are as high as 25 dB and 43 dB respectively. The modulator can operate with 10 GHz of modulation bandwidth and delivers -7 dBm power in saturation. For demonstration, the circuit is tested and shown to be capable of transmitting 4Gbps BPSK signal with NRZ rectangular pulses. The active chip area is 480μm× 260μm.