Exclusive OR/NOR 1C for 40-Gbit/s clock recovery circuit

The clock recovery circuit is a key component in high-speed electrical time-division multiplexing (ETDM) transmission systems. In the case of clock extraction from non-returnto-zero (NRZ) signals, differentiation and full-wave rectification are indispensable. Exclusive OR/NOR circuits (XOR) are widely used for this purpose. In this paper, we describe an XOR 1C fabricated with 0.1-/<m gate-length InAlAs/InGaAs/InP HEMTs for a 40-Gbit/s class clock recovery circuit. The 1C was configured with a symmetrical Gilbert cell type XOR gate and two types of peaking techniques are used to achieve its high bit-rate. On-wafer-measurements indicate that the 1C operates as fast as 80Gbit/s and can extract a 40-GHz frequency component from 40-Gbit/s NRZ input signals. To confirm the feasibility of using the packaged XOR 1C in clock recovery circuits, the conversion gain of the 1C, which was operated as a differentiator and fullwave rectifier, was evaluated. Assuming that the input to the clock recovery circuit is a 1 Vp-p signal, the relatively high output power of -17dBm can be obtained with low dependency on the length of the input pseudo-random bit streams. Furthermore, a clock recovery circuit was assembled using the packaged XOR 1C, a waveguide filter and a commercial amplifier; it offers the practical system-bit-rate of 39.81312 GHz with the low rms jitter of 900 fs.