Ka-band load modulated balanced amplifier using transformer-based quadrature hybrid coupler in 22 nm CMOS FD-SOI

Abstract

Faster wireless data transfer requires spectrally efficient modulation schemes, such as orthogonal frequency division multiplexing (OFDM) and higher-order quadrature amplitude modulation (QAM), which leads to a high peak-to-average power ratio (PAPR). This makes the efficiency of power amplifiers important not only at peak power but especially at the back-off power levels, as most of the time, the PA operates at power back-off. In this work, a dual RF input load modulated balanced amplifier (LMBA) with a transformer-based 3 dB hybrid coupler is designed by using a 22 nm CMOS FD-SOI technology to improve the back-off efficiency. A separate RF input source is used to drive the control amplifier, which injects the signal into the isolation port of 90° output power combining hybrid coupler. The control signal load modulates the impedance seen by the main amplifier (PA1 and PA2) dynamically with input drive (β), both resistively and reactively, achieving efficiency enhancement for 6 dB input power back-off (IBO) with a corresponding output power of 2.5 dB back-off from saturated power.

The main PAs (PA1 and PA2) and control PA (CA) use 3-stack pseudo differential power cells having a total width of 300μm and 180μm, respectively. At 26 GHz, the designed LMBA achieves maximum power added efficiency (PAE) of 23% with 21.7 dBm saturated power (Psat) and 23% at 2.5 dB output power back-off (OBO). The output referred 1 dB compression (OP1 dB) is 16 dBm with PAE of 15%.