A Ka-Band SiGe High-Gain Power Amplifier With Stability–Efficiency–Reliability-Enhanced Serial–Parallel Current-Reuse Technique

This article presents a 22–31-GHz high-gain power amplifier (PA) with a stability–efficiency–reliability-enhanced serial–parallel current-reuse technique for 5G communications. The existing current-reuse techniques basically rely on the stacked coupling approach, which will have a risk of generating negative output impedance, resulting in potential instability and oscillation of the amplifier. Second, considering efficiency and reliability, another major problem is that they are inapplicable to power stage design, especially multiway high power. To address these issues, a novel single-level uncoupled serial–parallel current-reuse technique is proposed and applied to power stage for the first time. With this technique, the dc path of the power stage is equivalent to multiple common-emitter (CE) amplifiers in cascaded sharing the same current, and the final consumed total current is small instead of the sum of the individual ways, which can significantly alleviate the pressure on current intensity requirements, thereby enhancing the reliability, while the RF path is multiple CE amplifiers in parallel rendering both higher efficiency and stronger stability. Furthermore, a self-cancellation-based AM–PM distortion compensation technique is adopted to attain high linearity without sacrificing performance or introducing dramatic design complexity. The proposed PA with both techniques is demonstrated in a 0.13- $\mu$ m SiGe BiCMOS technology with a chip area including PADs of 0.56 mm $^{{2}}$ . It exhibits a measured peak gain of 31.9 dB with 3-dB bandwidth of 22.7–30.7 GHz. At such a high power gain, the PA is still unconditionally stable over all measured frequencies. Besides, the PA achieves a 16.2-dBm saturated output power ( ${P}_{{\text{sat}}}$ ), a 13.9-dBm output 1-dB compression point power (OP $_{{\text{1dB}}}$ ), and a 20.5% peak PAE. Without applying any predistortion, the prototype realizes a measured AM–PM distortion till OP $_{{\text{1dB}}}$ point of ${<}1^{\circ}$ and gain expansion in the linear region of ${<}0.3$ dB at 28 GHz. Modulated signal measurements are also performed at 28 GHz with 2.4-and 3.2-Gb/s symbol rates. The PA achieves 9.3-dBm average output power with $-$ 32.9-dBc adjacent channel leakage ratio (ACLR) and $-$ 24.1-dB error vector magnitude (EVM).