A 60-GHz Variable-Gain Power Amplifier With a Switchable Inductor for TDD Systems

This letter presents a four-stage variable-gain power amplifier (VGPA) for 60-GHz time division duplex (TDD) phased array systems. To reduce the loading effect of the off-state VGPA on the receiver (Rx), a switchable inductor is proposed as an antenna transmit/receive switch (TRSW), which introduces low insertions loss to the VGPA output matching in transmitter (Tx) mode while providing a high off-impedance in Rx mode. To improve the output dynamic range, a Gilbert-based X-type variable-gain stage with low phase variation is designed. With measurements, the VGPA realizes a 25.4-dB peak gain with a BW $_{\text{{3\,dB}}}$ from 49 to 67 GHz, and a $<$ 2.6 $^{\circ}$ rms phase error is achieved over a 15-dB gain tuning range. The measured OP $_{\text{1\,dB}}$ , $P_{\text{sat}}$ , OIP $_{\text{3}}$ , PAE $_{\text{1\,dB}}$ , and PAE $_{\text{max}}$ are 11.3, 12.2, 16.2 dBm, 6.4%, and 8.9%, respectively. When the PA and the switchable inductor are turned off, a $>$ 180 $~\Omega$ output off-impedance is achieved over the interested frequency range.