A Variable Gain Power Amplifier Based on Switched-Capacitor Array With Stable Linearity

This brief proposes a variable gain power amplifier (VG-PA) with stable linearity for n257/n258 frequency band applications. A switched-capacitor array is proposed in the cascode (CC) circuit to control the gain while maintaining linearity. A compensation inductor is introduced between the common-emitter (CE) and common-base (CB) transistors to suppress the phase variation. For the proof of concept, the VG-PA was fabricated in a 0.13-
$\mu \text{m}$
SiGe BiCMOS technology with a core size of 0.59
$\times $
0.46 mm
²
. Measurements show that at 24/26/28/29.5 GHz, over 5.7/5.5/7.0/7.5-dB gain tuning range, the output 1-dB compression point (OP1dB) is better than 14 dBm with
$ {\Delta }$
OP1dB less than 1.2 dB, the third-order output intercept point (OIP3) is better than 22 dBm with
$ {\Delta }$
OIP3 less than 3.4 dB, and the phase variation (
$ {\Delta }{\varphi }$
) is from 3 to 9.5°. To the author’s best knowledge, this work has the lowest linearity variation among Si-based variable gain amplifiers at millimeter-wave frequency band.