A PHYSICALLY-BASED SMALL-SIGNAL CIRCUIT MODEL FOR HETEROSTRUCTURE ACOUSTIC CHARGE-TRANSPORT DEVICES

A physically based small-signal circuit model for GaAs-AlGaAs Schottky gate heterostructure acoustic charge transport (HACT) devices is pres ented. Analytical expressions for the instantaneous and average channe l current as a function of gate voltage are obtained from physical dev ice parameters. The charge injection model is based on subthreshold cu rrent models for GaAs MESFET's. It is shown that the shape of the samp ling aperture of the charge injection operation is approximately Gauss ian. Good agreement is obtained between the measured dc channel curren t versus gate voltage and that predicted by the model. Equivalent circ uits are also developed for the transfer and output sensing operations . Expressions for noise sources due to the physical processes that occ ur within the device are developed. Thermal noise, shot noise, and tra nsfer noise are treated. The form of the analytic expressions for freq uency response and noise figure allows easy implementation on commerci ally available CAE software. Simulations of both gain and noise figure performed on Libra(TM) are compared to measured data. Simulations agr ee with 10 percent of measured frequency response for a 160 tap HACT d evice. The predicted noise figure agrees within 1 dB of that measured for the same device.