David E. Meharry

Multi-Watt Wideband MMICs in GaN and GaAs

A comparison is presented of 4 to 18 GHz MMIC power amplifiers implemented in AlGaN-GaN HEMT and GaAs PHEMT with common circuit design technology. Both GaN and GaAs MMICs were designed as non-uniform distributed power amplifiers and achieved approximately 4 Watts over the band. The circuit complexity of the GaAs circuit is much greater than for GaN, as shown by the relative transistor output peripheries of 14.4 mm and 2 mm. The authors believe that both the GaN and GaAs MMICs have higher power than any published result of comparable bandwidth.

Decade Bandwidth Planar MMIC Balun

A planar MMIC balun covering 2 to 20 GHz has been demonstrated with better than plusmn1.2 dB amplitude and plusmn9 degrees phase accuracy. This 1.2times1.5 mm2 circuit is a novel connection of a 2 to 7 GHz spiral coupled line balun, a 6 to 20 GHz coupled line balun, and lumped diplexer filter components with absorbed parasitic elements from the two baluns

Reduction of Noise in Wideband Distributed Amplifiers

A general solution is presented to a classical problem in wideband distributed amplifiers, a noise figure characteristic that increases at low frequencies to values much higher than the underlying transistor noise capabilities. Early studies showed that this is caused by the input line termination resistor, but this understanding has not been used to implement circuits with improved noise figure. We report that an effective solution is the recasting of the input artificial transmission line into a transformer filter that matches the more favorable high resistor values to the external impedance. Improvements of about 1 dB in noise figure at the lowest frequency of operation for a 2 to 18 GHz distributed amplifier are demonstrated.

A Q-Band MHEMT 100-mW MMIC power amplifier with 46 % power-added efficiency

A Q-band MMIC power amplifier has been designed, processed, and measured with first pass success. Design parameters include 20 dBm power, 25 dB gain, 40 % PAE, input return loss of 10 dB and output return loss of 6 dB across 43.5 to 45.5 GHz. The MMIC design is based on the BAE Systems 0.1 μm MHEMT device, which has high gain and excellent PAE. The two-stage amplifier uses a 2-finger, 75 μm unit gate width, 0.1 μm gate length MHEMT device for the first stage and two 4-finger, 75 μm unit gate width, 0.1 μm gate length MHEMT devices for the output stage. Complete stabilization for both the even and odd mode is provided using feedback and resistors in critical locations of the circuit. The first stage is optimized for gain while the output stage is optimized for power and power-added efficiency (PAE). The complete MMIC amplifier measures 3.5 mm × 1.7 mm complete with dc blocks and dc biasing elements. Measured performance includes record high PAE of 46 % at 44.5 GHz, 24 dB small-signal gain, 1 dB compressed power of 18 dBm, and 3-dB compressed power of 20.5 dBm across the 43.5 to 45.5 GHz frequency band.