High-speed QPSK modulator and demodulator with subharmonic pumping

The authors describe a subharmonically pumped QPSK modulator and demodulator using pairs of beam-leaded Schottky diodes and appropriate high-pass and low-pass filters on dielectric substrates. A modulator and a demodulator were operated in cascade at a carrier frequency of 13 GHz with a common pump at 6.5 GHz. This circuit showed clean eye diagrams of the recovered data trains up to 1.5 Gb/s with corresponding error rates of less than 10^-11. The circuits can be readily scaled to higher frequencies with a proportional increase of the information rate