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High Power J-FET Analog Switch

IP.com Disclosure Number: IPCOM000050091D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Olsen, FW: AUTHOR

Abstract

Low leakage, high current junction field-effect transistors (J-FETs) can be used reliably in series for controlling large analog voltages by insuring that the voltage drop across each device is maintained within acceptable limits.

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High Power J-FET Analog Switch

Low leakage, high current junction field-effect transistors (J-FETs) can be used reliably in series for controlling large analog voltages by insuring that the voltage drop across each device is maintained within acceptable limits.

Referring to the figure, a pair of J-FETs 1, 2 in series are used to control an analog voltage that exceeds the capability of a single J-FET. An acceptable voltage across each J-FET is insured by the use of a voltage divider of series resistors 3 and 4 interconnected with the supply potentials through respective operational amplifiers 5, 6 used as voltage followers. The resistor junction is further connected to the switched line 7 through resistor 8 which serves as a guide loosely holding the line mid-point at one half the analog switch "stand off" voltage.

J-FETs 1 and 2 are controlled through their respective gates 9 and 10 that are in turn switched by the signal level input to J-FET 11. A high voltage level at the input turns on J-FET 11 which, via resistors 12 and 13, turns on V-FET (VMOS FET) 14 to drop the voltage through resistors 15, 16 and diodes 17, 18 to lower the voltage at gates 9, 10 of respective J-FETs 1, 2. This holds J-FETs 1 and 2 off. Resistors 12 and 13 absorb the voltage differences through the analog input range. The output of each voltage follower 5, 6 is connected through a respective Zener diode 19, 20 and resistor 21, 22 to a negative potential. A capacitor 23 is in parallel with...