Phase-Locked Loop Frequency Synthesizer for Satellite Receivers
Zhiming Deng and Ali Niknejad
The LNB (low noise block) in a satellite TV receiver down-converts the entire Ku-band (10.7-12.75 GHz) to an intermediate IF, ranging in the L-band (0.95 GHz-2.15 GHz). The goal of this project is to integrate the complete front end receiver (LNA, mixer, frequency synthesizer) in CMOS technology. An integrated CMOS approach will drastically reduce the costs for such receivers.
The frequency synthesizer is a critical part in the front end receiver. Current solutions employ dielectric resonant oscillators (DRO) for good frequency stability. A PLL has a much smaller footprint but must achieve very low phase noise over a wide output frequency range (10 GHz-11.3 GHz). The design of the frequency synthesizer will be accomplished in two steps. First, a low phase noise and low power VCO is designed, fabricated, and characterized. Second, a phase-locked loop frequency synthesizer will be designed and fabricated and integrated with the rest of the LNB blocks (described separately). A new VCO topology has been proposed for low power consumption. The VCO can oscillate at two different frequencies while only one current branch is required. A test chip (Figure 1) has been fabricated in standard CMOS technology and the functionality has been verified. The spectrum analyzer plot clearly shows two oscillation frequencies generated by the custom dual mode resonator.
Figure 1: Output spectrum of a dual-mode VCO