A 110-to-130 GHz SiGe BiCMOS Doherty Power Amplifier With a Slotline-Based Power Combiner

This article presents a D-band Doherty power amplifier (PA) featuring a low-loss and compact slotline-based eight-way power combiner to improve the saturated output power and power back-off (PBO) efficiency. The proposed combiner consists of grounded coplanar waveguides (GCPWs), slotlines, and SLOT-GCPW coupling structures. Instead of the conventional transformer structure, the proposed SLOT-GCPW coupling structure effectively reduces insertion loss, increases the common-mode rejection, and encounters a comfortable symmetrical compact layout. More importantly, the proposed combiner can also be applied to achieve impedance inverters for active load modulation in a compact size. Based on the proposed multiway combining Doherty PA prototype, a high-efficiency and high-output D-band PA is implemented in a 130-nm SiGe bipolar CMOS (BiCMOS) with f(iota) / f(max) of 350/450 GHz. The extremely compact power combiner leads to a small PA core area of 1.1 x 0.53 mm(2). The PA achieves a peak small-signal gain of 21.8 dB with 3-dB bandwidth from 107 to 135 GHz. At 110/120/130 GHz, the PA achieves 22.7/22.6/22.4 dBm P-sat with 18.7%/17.2%/16.1% peak power-added efficiency (PAE) and 12.1%/11.7%/9.8% PAE at 6-dB PBO from P-sat. Modulation measurement with single-carrier 16-quadrature amplitude modulation (QAM) and 64-QAM signals has been performed. For a 2-GHz 16-QAM signal, the PA achieves 13.74 dBm P-avg and 7.88% average collector efficiency with 11.6% error vector magnitude (EVM) at 131.5 GHz. The PA also supports a 2-GHz 64-QAM signal, achieving 13.76 dBm P-avg and 7.92% average collector efficiency with 11.9% EVM at 131.5 GHz.