A 43-Gb/s full-rate clock transmitter chip for SONET OC-768 transmission systems is reported. The IC is implemented in a 0.18-μm SiGe BiCMOS technology featuring 120 GHz fT and 100 GHz fmax HBTs. It consists of a 4:1 multiplexer, a clock multiplier unit, and a frequency lock detector. The IC features clock jitter generation of 260 fs rms and dissipates 2.3 W from a -3.6-V supply voltage. Measurement results are compared to a previously reported half-rate clock transmitter designed using the same technology.