A high-speed multimodulus HBT prescaler for frequency synthesizer applications

A high-speed variable modulus prescaler that divides the input clock frequency by 128 up to 255 with unit step increment has been implemented with heterojunction bipolar transistor (HBT) technology. A maximum operating frequency of 9.72 GHz with power consumption of 650 mW has been measured. The high-speed performance is attributed to the circuit design, which minimizes the critical path delay, and the intrinsic high-speed characteristics of HBT technology. The phase noise of the prescaler is important for frequency synthesizer applications. With 6.24-GHz input frequency, the phase noise was -110 dBc/Hz at 100-Hz offset frequency and -120 dBc at 1-kHz offset frequency. The noise floor decreases as the input frequency decreases. Phase noises of -125 dBc/Hz at 100-Hz offset and -135 dBc/Hz at 1-kHz offset were obtained for a 1.2-GHz input frequency. >