A Frequency Doubler With Second Harmonic Feedback for Wideband, Efficient Frequency Multiplication at Millimeter-Wave

Frequency multipliers are widely used in scalable millimeter-wave (mm-wave) arrays in communication and radar. This article presents an mm-wave frequency doubler (FDB) topology that exploits odd-mode/even-mode operation to create different feedback networks at the fundamental frequency and second harmonic. Theoretical analysis of the FDB network is detailed. The FDB topology is well-suited for CMOS integration, and a stand-alone FDB in 65-nm CMOS achieves a saturated output power ( $\boldsymbol{P_{\text{sat}}}$ ) of $\boldsymbol{>}$ 10.1 dBm with a maximum drain efficiency (DE) of 32.7% at 60 GHz. The wideband FDB is also cascaded with a power amplifier (PA) to achieve a total $\boldsymbol{P_{\text{sat}}}$ of 15 dBm with a maximum dc-to-RF efficiency ( $\boldsymbol{\eta_{\text{total}}}$ ) of 24.5%. Measurements demonstrate wideband FDB chirp bandwidths and suitability for frequency-modulated continuous wave (FMCW) radar applications.