FBH research: 28.11.2016

First W-Band InP DHBT Digital Power Amplifier

W-band DPA
Fig. 1: Schematic of realized W-band DPA including collector bias feed and band-pass filter (left); fabricated InP DHBT DPA MMIC (right) for 95 GHz; chip area (w/ pads): 0.51 x 0.53 mm2
Collector efficiency & PAE for varying collector voltages
Fig. 2: Measured collector efficiency (ηC) and power-added efficiency (PAE) for varying collector voltages VC (1 … 2.7 V) and 10 and 12 dBm input power vs. output power (Pout); VB = 0.85 V.

Emerging system applications including future high-speed communications, high resolution radar/imaging systems and directed energy are driving the need for W-band power amplifiers (PA). In general, two PA parameters are subject and target of intensive research: high output power and high efficiency. For obvious reasons, the higher the transmitted power the larger is the transmission range, while a high efficiency extends battery lifetime, saves energy and reduces system complexity as well as cost.

Common power amplifiers in the millimeter wave range apply analog PA approaches like class-A, -AB, or even class-E design. As these types of PAs are narrowband and the transistors require a proper input and output matching they are limited in terms of flexibility and compactness. To overcome these restrictions, the digital PA approach is a suitable candidate, well proven in the lower GHz-range, but never employed in the sub-THz region so far.

Recently, FBH presented at the European Microwave Week 2016 in London for the first time a high-efficiency W-band power amplifier, the design of which follows the digital PA approach. The PA is realized as MMIC in the FBH 0.8 µm InP DHBT transferred-substrate process. It utilizes a double-emitter-finger DHBT unit cell with an emitter area of 2 x 0.8 x 6 µm2. It includes a band-pass filter at the output with 0.6 dB insertion loss and 24 dB input return loss at the signal frequency of 95 GHz. Moreover, it does not use any special reactive matching.

Applying an overdriven sinusoidal input signal to emulate digital operation the digital PA (DPA) reaches a maximum Pout of 14.4 dBm and a peak PAE of 31% at a signal frequency of 95 GHz. Collector efficiencies of more than 80% demonstrate the great potential of the DPA concept for future high-speed communications where extreme signal bandwidths above 1 GHz are required.

Publication

A. Wentzel, M. Hossain, D. Stoppel, N. Weimann, V. Krozer, and W. Heinrich, "An Efficient W-Band InP DHBT Digital Power Amplifier", Proceedings of the 11th European Microwave Integrated Circuits Conference (EuMiC) 2016, pp. 21 - 24, London, UK.