Low Voltage performance of Microwave CMOS Gilbert Cell Mixers

Low Voltage performance of Microwave CMOS Gilbert Cell Mixers

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IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 32, NO. 7, JULY 1997 1151 Low Voltage Performance of a Microwave CMOS Gilbert Cell Mixer P. J. Sullivan, B. A. Xavier, and W. H. Ku Abstract— This paper demonstrates the low voltage operation of a doubly balanced Gilbert mixer fabricated in a 0.8- m CMOS process and operating as both a down-converter and an up- converter. As a down-converter with an RF input of 1.9 GHz, the mixer has a single sideband noise figure as low as 7.8 dB and achieved down-conversion gain for supply voltages as low as 1.8 V. As an up-converter, the mixer demonstrates 10 dB of conversion gain at an RF frequency of 2.4 GHz with an applied local oscillator (LO) power of 7 dBm and LO-RF/LO- IF isolation of at least 30 dB. Up-conversion gain was achieved over a 5-GHz bandwidth and at supply voltages as low as 1.5 V. The mixer presented demonstrates the lowest single side band noise figure for a CMOS doubly balanced down-converting mixer and the highest frequency of operation for a mixer fabricated in CMOS technology to date. Index Terms— CMOS integrated circuits, frequency conver- sion, microwave measurement, microwave mixer, mixer noise, mixers, power demand, scattering parameters measurement. I. I NTRODUCTION A CMOS RF up/down converter would allow a consider- able increase in transceiver integration and a reduction in transceiver cost. A low supply voltage is desired for hand-held wireless applications to reduce the weight from the number of stacked battery cells and for the corresponding reduction in power dissipation in the digital circuitry. Mixers are an especially important building block in transceiver design, because the receiver dynamic range is often limited by the first down-conversion mixer. The design of mixers forces many compromises between conversion gain, local oscillator (LO) power, linearity, noise figure, port-to-port isolation, volt- age supply, and current consumption. The most fundamental choice in FET mixer design is whether to use an active or a passive mixer. Active FET mixers achieve conversion gain and require lower LO power than their passive counterparts. Passive FET mixers (operating FET’s in the linear region) are a well-known mixing technique; they typically demonstrate conversion loss and excellent intermodulation performance at the expense of LO power [1], [2]. A reduced LO drive is a significant advantage in low-voltage/low-power IC design be- cause large LO drives are difficult to generate in a low-voltage environment and result in an increase in power dissipation. This also dictates increased LO-RF/LO-IF isolation in order to maintain the same rejection as would be obtained with a lower LO drive. The primary advantage of a passive mixer Manuscript received November 20, 1996; revised January 22, 1997. This work was supported in part by the NSF ICAS Center Award No. EEC-94- 19520.
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