CMOS Yields 9-To-31-GHz Subharmonic Passive Mixer

Silicon-CMOS Technology has rarely been associated with millimeter-wave signal-processing applications. But Mingquan Bao and associates from the Microwave and High Speed Electronics Research Center at Ericsson Research (Molndal, Sweden) have designed and fabricated a subharmonic, passive down-conversion mixer in 90-nm silicon CMOS capable of operating with RF signals from 9 to 31 GHz. The mixer incorporates a single transistor and runs in local-oscillator (LO) source-pumped mode, with the LO signal applied to the source of the device and the RF signal applied to its gate.

When driven with an LO signal with frequency that is only one-half of the expected fundamental frequency, the conversion loss is as low as 8 to 11 dB over the RF range of 9 to 31 GHz. The down-conversion mixer has an intermediate-frequency (IF) range of DC to 2 GHz. The mixer can also operate in gate-pumped mode. It is based on an optimized transistor layout with a device having a transition frequency of 170 GHz and maximum frequency of oscillation of 240 GHz. The CMOS process was used to fabricate a mixer chip measuring 0.94 X 1.0 mm including pads.

The CMOS mixer was measured on wafer in different subharmonic modes including with a source-pumped LO signal with frequencies that were one-half that of a fundamental mixer and one-third that of a fundamental mixer. For a fixed IF of 1 GHz, the conversion loss in the first mode of operation was about 8 to 12 dB, and about 12 to 16 dB in the second mode of operation. See “A 9-31-GHz Subharmonic Passive Mixer in 90-nm CMOS Technology,” IEEE Journal of Solid-State Circuits, October 2006, Vol. 41, No. 10, p. 2257.