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Digital Driver With Mesfets Having Three Different Threshold Voltages

IP.com Disclosure Number: IPCOM000062537D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Baechtold, W: AUTHOR

Abstract

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.

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Digital Driver With Mesfets Having Three Different Threshold Voltages

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. For the load MESFETs, both implants are superimposed whereby a proper threshold of approximately -.75 V is obtained. Fig. 1 shows a circuit diagram of a source follower driver circuit with a source follower device exhibiting a "third level" threshold of -.15 V. The thresholds of the other MESFETs are .15 V for the E-type and -.75 V for the D-type devices. Fig. 2 shows a push-pull driver with driver MESFET thresholds of -.15 V.

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