Digital Driver With Mesfets Having Three Different Threshold Voltages
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Digital high speed MESFET driver circuits requiring a source follower and providing proper logic output levels are difficult to realize with the two thresholds (VtD, VtE) provided by conventional enhancement/ depletion (E/D) devices. The invention suggests that substantial improvement can be achieved by using a source follower MESFET having a different, third threshold voltage somewhere between VtD and VtE . The implementation of this third threshold can be obtained without any additional processing steps. As in conventional E/D fabrication processes, two channel implants are made: first, a normal E implant resulting in a VtE of .15 V, and a second implant which provides a slightly negative threshold of -.15 V, corresponding to the desired threshold for the source follower device.