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SESSION VIII: GUNN and IMPATT DIODE CIRCUITS Chairman: James W

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SESSION VIII: GUNN and IMPATT DIODE CIRCUITS Chairman: James W SESSION VIII: GUNN and IMPATT DIODE CIRCUITS Chairman: James W. Gewartowski Bell Laboratories WPM 8.1: Ku-Band MIC GaAs IMPATT Amplifier Modules” Allentown, PA Hua Quen Tserng and David N. McQuiddy Texas Instruments, Inc. Dallas, TX THIS PAPER WILL DISCUSS thc development of a Ku-band Figure 4 shows the gain-frequency response of a four-stage solid-state transmitter consisting of GaAs IMPATT and Read power amplifier. Output power of 4 W with 20-68 gain was diodes operating in a microstrip circuit environment to provide obtained. This amplifier is centered at a frequency of 13.5 GHz amplification with a minimum of 63 dB small-signal gain and with a 1-dB bandwidth of 1.1 GIIz. The ovcrall power-added a minimum compressed gain at a 5-W output of 57 dB over a efficiency is about 150/. The circuit layout for the four-stage 250-MHz bandwidth centered at 13,525 GHz. power amplificr is similar to that of the preamplifier shown in Development of a multistage reflection amplifier using GaAs Figure 1, except for thc addition of onc more stage. IMPATT and Read diodes was selected as the approach to One of the major problems to bc overcome for the Read achieve high-power, high-gain goals. To facilitate testing diode amplifiers is the large change in diode negative rcsistancc and tuning, the transmitter has been separated into two that accompanies an incrcase in the input drive Icvcl. It has amplifiers. The preamplifier consists of three GaAs IMPATT been observed that the high-power, high-efficiency mode of amplifier stages in cascade. The power amplifier utilizes operation can only be achieved with a substantial RF voltage high low-profile GaAs Read diodes as the negative resistance swing across the diode aceompanicd by a large de current elements for increased power and efficiencies. modulation. This is due to the fact that depletion width The preamplifier was designed to provide 36 dB of gain at modulation plays an important role in high-efficiency operation. input signal levels of -20 dBm or less. Figure 1 shows a Generally, the circuit impedance required to maximize the photograph of the preamplifier. A broadband (11 to 16 GHz) power-added efficiency ai large-signal drive conditions and MIC circulator suitable for use in the reflection amplifier was produce a gain on the ordcr of 6 dB or more will result in a developed. The circulator-isolator chain and the coupling small-signal gain in execss of 20 dB. This high small-signal gain networks have been fabricated on single-ferrite and alumina is not desirable in a cascaded amplifier, since it will be difficult substrates, respectively. Unpackaged diodes with integral to prevent thc amplifier from breaking into spurious oscillation, plated heatsinks were mounted on small gold-plated copper once the RF input signal is removed. Figure 5 shows the blocks for attachment to thc microstrip circuit. A quarter- operating I-V characteristics of an amplifier using a doub1t:- wave, parallel-coupled filter section was used as the dc mesa diode. The bias state for maximumefficiency and block. The amplifier circuits consist of two quarter-wave output power of the amplifier can be reached by a carcful transformer section with provision for fine microwave tuning. sclection of the bias circuit load line. Figure 2 shows the microwave performance characteristics Figure 6 shows the gain-frequency response of a cascaded of the preamplifier at several input power levels. A single, amplificr. At the highest input level of -20 dBm, this amplifier common bias voltage of 42 V was applied to the amplifier. provided 4(.5Ri of output power with 56.5 dB gain. A gain of The unit dissipates 2.5 W (60 mA at 42 V) with no extcrnal 65.5 dB was obtained with 3.5 W output when the input level cooling required. was dropped to -30dBm. Prior to the integration of the power amplifier stages, In summary, it was possible to: Read diodes were characterized in a variety of amplifier Design widcband (11-16 GHz) circulators suitable circuits. It has been found that a circuit of the same type for use in reflection-type amplifiers using CaAs used for the preamplifier stages can be used successfully. IMPATT and Schottky-Read diodcs. A single-stage, single-mesa amplifier has demonstrated 6-dB Build a compact (2” x 1.2” x 0.6”) thrcc-stagc gain and 22.4% power-added efficiency with 2 JV CW output IMPATT amplifier in MIC form with a small-signal power. The 1-dB bandwidth is 1GHz(l3 to 14GHz). gain in excess of 30 dB, and a maximum dc input To achieve a 5-W output power goal, double-mesa Read power of only 2.5W. diodes were used in single-stage microstrip amplifier circuits Provide a single-stage, single-mesa amplifier with a for use in the last stage of the power amplifier. The highest 6-dB gain and 22.4yo power-addcd efficicncy with output power obtained was 5.9 W at 4-dB gain and 22Yo power 2WCW output power. Additionally, a douhle-mesa added efficiency at a frequency of 13.5 GHz. Figure 3 shows diode amplifier produced an output power of the RF performance of this amplifier as a function of the RF 5.9W at 4-dB gain with 22% efficiency. input levels. Produce a four-stage power amplifier affording 4W __ output power at 20-dB gain. Cascade a preamplifier and power amplifier to *Project supported by NASA Goddard Sgace Flight Center, Greenbelt. MD, under Contract No. NAS5-20894. achieve an overall gain of 56.5 dB with 4.5W output. 46 Acknowledgments I I I I I I I I FREQUENCY (GHz) FIGURE 1-Photograph of integrated preamplifier. FIGURE2-Performance characteristics of preamplifier shown in Figure 1. FRE3UENCY :13 4 GHz RF INPUT = + 16 dBm 30 - mLL 28 - O~~~~"~IIIl1,I06 OB 12 0 JO 26 ' I 16 20 24 12 55 13.55 14.55 RF INPUT POWER (WATTS1 FREQUENCY (GHzl FIGURE3-RF performance of double-mesa,singlestage FIGURE 4-Gain-frequencyresponse of four-stagepower Schottky-Read amplifier. amplifier. 500 I 36 RF INPUT (dhl 33 7 34 31 7 ..... 287 I E - 32.7 g 32 ;i 300 I c m LT 3 26 I- 24 [ 1 I 130 13.5 14 0 FREQUENCY (GHz) FIGURE 6-Microwave performance of a cascaded amplifier. .
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