A Dual-Core 60 GHz Push-Push VCO with Second Harmonic Extraction by Mode Separation

Abstract

In this work we present a 60 GHz dual-core push-push Colpitts VCO in 0.13) µm SiGe BiCMOS technology. We propose a circuit technique to extend a Colpitts VCO to a dual-core operation. Additionally, we propose a novel circuit technique that enables extraction of the second-harmonic from a VCO core for push-push operation by means of mode-separation. The principle takes advantage of the fact that the second harmonic is present in a differential VCO in a common-mode. Hence, the fundamental signal can be coupled out from a VCO in differential mode, whereas the second harmonic signal can be coupled via the common-mode. This enables extraction of signals, without loading the VCO core directly by input capacitance of the following buffer stages, which might deteriorate the phase noise. The VCO achieves in measurement a low phase noise of −107 dBc/Hz at 1 MHz offset at 62 GHz and an output power of −1.9 dBm. The VCO including buffer, biasing and frequency divider dissipates in dual-core operation 112 mA, whilst a single VCO core consumes only 24 mA from a single 1.8 V supply. The chip consumes area of 0.95 mm2 including pads, buffer and frequency divider chain.