Browse Prior Art Database

Low Level Differential Capacitive Hold Multiplex Switch

IP.com Disclosure Number: IPCOM000093450D
Original Publication Date: 1967-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Hall, TK: AUTHOR

Abstract

Field effect transistors FET's 10 and 12 provide a multiplexing function. A charge stored on capacitor 14 controls the operation of FET's 10 and 12. If they are normally on FET's, the charge holds the device off. If they are normally off devices, the charge on capacitor 14 holds them on. Regardless of the FET type employed, it is desirable to build up the charge on capacitor 14 rapidly, maintain it at a relatively constant level, and discharge it sharply.

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Low Level Differential Capacitive Hold Multiplex Switch

Field effect transistors FET's 10 and 12 provide a multiplexing function. A charge stored on capacitor 14 controls the operation of FET's 10 and 12. If they are normally on FET's, the charge holds the device off. If they are normally off devices, the charge on capacitor 14 holds them on. Regardless of the FET type employed, it is desirable to build up the charge on capacitor 14 rapidly, maintain it at a relatively constant level, and discharge it sharply.

To accomplish this, diodes 16 and 18 are provided as well as a discharge device, such as silicon controlled rectifier SCR 20. Transformers 22 and 24, with a source of potential and associated switches SW1 and SW2, complete the circuit diagram. When SW1 is closed, the potential applied to transformer 22 develops a pulse across the output of transformer 22. A charge rapidly builds up on capacitor 14 and FET's 10 and 12 are set to the proper state, on or off. They stay in that state until the charge decays on capacitor 14 or until capacitor 14 is discharged purposely. Diodes 16 and 18 prevent the charge from decaying or drooping. In order to discharge capacitor 14, SW2 is closed and a pulse is developed across the windings of transformer 24. This breaks down SCR 20 and allows capacitor 14 to discharge. FET 10 then changes state, as does FET 12.

In operation, analog input signals are applied across terminals 26 and 28. They are passed on, or not, to terminals 3...