A Wideband Balanced Amplifier Using Edge-Coupled Quadrature Couplers in 0.13-μm SiGe HBT Technology

In this work, a wideband millimeter-wave (mm-wave) power amplifier (PA) is reported. To provide excellent input/output impedance matching across broadband, sufficient output power and high power-added efficiency (PAE), a balanced amplifier (BA)-based architecture is used in designing this PA. In particular, an edge-coupled quadrature coupler is designed as its RF-power-division/combination block, and its performance in terms of magnitude/phase balance error is minimized throughout a relatively wide bandwidth. A PA prototype is fabricated in 0.13- $\mu \text{m}$ SiGe HBT technology and tested. Under a 1.6-V power supply, the variation of small-signal gain is less than 3 dB within 20-40 GHz, which is equivalent to more than 66% fractional 3-dB bandwidth. Within this frequency range, at least 15.8 dBm saturated output power could be delivered with the peak PAE higher than 16.8%. The designed PA supports a single-carrier 200-MHz 64-quadrature amplitude modulation (QAM) with higher than 12.8-dBm average output power, while still maintaining an error vector magnitude (EVM) below −25 dB at 30 GHz. The size of the designed compact-size PA, including all pads, is only 0.7 mm $\times1.3$ mm.