An ultrahigh-speed GaAs MESFET operational amplifier

A wide-bandwidth GaAs MESFET operational amplifier is reported, with a 65-dB DC gain and a 20-GHz gain-bandwidth product at 500 MHz. The circuit uses a variety of local feedback techniques to enhance the overall gain. The use of an undoped GaAs buffer, grown at a relatively low temperature ( approximately=300 degrees C), eliminates backgating and light sensitivity. The circuit was fabricated in an 80-GHz f/sub T/ MESFET process, with 0.2- mu m electron-beam defined gates. The high levels of 1/f noise, MESFET frequency-dependent output conductance, and large offset voltage standard deviation limit the application of the circuit to moderate precision applications.<
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