Negative-Resistance Cell Benefits Millimeter-Wave CMOS VCO

Many advanced communication and sensor systems include millimeter-wave voltage-controlled oscillators (VCOs) as key components. Recently, such devices have been realized in CMOS technology. Compared to III-V compound devices or silicon-germanium (SiGe) HBT, CMOS devices boast lower unit current-gain frequency and maximum oscillation frequency. It is therefore essential to investigate the highfrequency behavior of a negative-resistance cell when designing millimeter-wave CMOS VCOs. In fact, an LC source-degeneration negative-resistance cell of an LC VCO has been investigated by Ping-Chen Huang, Ming-Da Tsai, George D. Vendelin, Huei Wang, Chun-Hung Chen, and Chih-Sheng Chang of National Taiwan University and Taiwan Semiconductor Manufacturing Company (TSMC).

The researchers show that an LC sourcedegeneration negative-resistance cell has a better frequency response to operate at millimeter- wave range under low power consumption. By employing the push-push principle, they were able to obtain an output frequency beyond the maximum frequency of oscillation, fmax.

Specifically, a 114-GHz push-push fully integrated LC VCO was used to demonstrate the LC source-generated topology. It is implemented in TSMC’s 0.13-μm process. With core power consumption of 8.4 mW, the tuning range is 56.4 to 57.6 GHz at the fundamental port and 112.8 to 115.2 GHz at the push-push port. At 10-MHz offset, the measured phase noise at the fundamental port is −113.6 dBc/Hz. See “A Low-Power 114-GHz Push-Push CMOS VCO Using LC Source Degeneration,” IEEE Journal of Solid-State Circuits, June 2007, p. 1230.

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