Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 5, NO. 1, WINTER 1993

This article describes a 1-watt, broadband MMIC power amplifier design using lossy matching networks in the form of a bridged-T all-pass network. This approach offers the advantage of exceptional gain flatness, low input VSWR, high efficiency and small size. A two stage amplifier is described that delivers greater than 1 watt across the 2 to 6 GHz range with a linear gain of 19 dB, and input VSWR below 1.7, a power-added efficiency of 25 percent and a chip area less than 4.4 mm ².

In broadband power amplifier design, a key element is maintaining flat gain over the band while achieving a well matched input (good input VSWR). Commonly, this is addressed using the balanced amplifier approach, whereby the input is reactively matched for gain sloping (equalization) and quadrature couplers provide a good match when two similar amplifier stages are placed between them. Although very common in hybrid microwave integrated circuits (MICs), the quarter wavelength size of the couplers is usually not practical for monolithic MICs (MMICs).

Another approach often used with MMICs is the distributed amplifier, which offers large bandwidth, excellent gain flatness and low input VSWR. On the other hand, it has low gain, low efficiency and requires a relatively large chip size.

The distributed amplifier approach...