A High-Speed Depletionmode Dmos Fet For Small Signal Applications

42 EE September 1988 A HIGH-SPEED DEPLETION- MODE DMOS FET FOR SMALL SIGNAL APPLICATIONS by Alan Pritchard This article describes a new ultrahigh-speed n-channel depletion- mode lateral DMOS transistor geared for small-signal applications. This device boasts high-performance characteristics, which in- clude tunr-on speeds of less than 1 ns; low reverse-transfer capacitance of less than 2.5 pF; high-frequency transconductance greater than 10 ms; a wide dynamic range; and low distortion. Fig. la and lb show idealized cross- sections of the "normally-on" depletion mode and "normally-off" enhancement- mode devices. Because these device structures are similar, the device characteristics are also similar. In fact, the depletion-mode device may be thought of as an enhancement-mode device with a negative threshold voltage. 2 200 A=920 B=100S2 their low drain capacitance, which makes them suitable for biasing appli- cations in low-input leakage, medium- speed (>50 V/0) circuits. Fig. 4 sho...