Switch uses a combination of N-channel and P-channel Metal Oxide Semiconductor Field Effect Transistors /MOSFET/ to obtain a normally open switch with no power applied. Series-shunt-series MOSFET switching achieves high input-output isolation

Magee, R. L.

Trowbridge, L. E.

English

NASA Technical Reports Server

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April 1970	 Brief 70-10022 
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L	 NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Tederal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, DC. 20546. 
Solid State Switch Provides High Input-to-Output Isolation 
- 
Gating Voltage 
How it's done: 
As shown in the schematic, a P-channel MOSFET 
(Qi) accomplishes the primary purpose of discon-
necting the input signal voltage from the output with-
out introducing an objectional level of offset voltage. 
An N-channel junction MOSFET (Q2) provides a 
rapid turnoff capability because of its low "on" re-
sistance. In order to prevent a short circuit, another 
MOSFET (Q3) is used to switch simultaneously with 
Qi, thus isolating the output from the shunt element. 
This leaves the output voltage at the cutoff level. 
The switching voltage waveform is delayed for a 
few nanoseconds before it is applied to the gate of Q3, 
(continued overleaf) 
..
The problem: 
To design a solid state switch capable of interrupt-
ing electronic signals in the 10 mV to 80 V peak-to-
peak range, with input-to-output isolation of 80 db, 
at a rate of 50,000 samples per sec. 
The solution: 
A solid state switch using a combination of N- and 
P-channel metal oxide semiconductor field effect 
transistors (MOSFET) to obtain a normally open 
switch with no power applied. High input-output 
isolation is achieved through the use of series-shunt-
series MOSFET switching. 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000022 2020-03-16T23:59:56+00:00Z
allowing the voltage charge on the load reactance to 
discharge through Q3 and Q2 to ground, turning off 
Q3, and disconnecting the load from the switch. This 
procedure energizes other switches connected to the 
same load, allowing measurements to be made of 
signals from other sources in rapid succession. The 
switch must remain off when no power is applied to 
the driver. This is accomplished by adding another 
MOSFET (Q4) to the circuit, ahead of Ql. Q4 has 
an opposite polarity to that of Qi andQ2; therefore, 
any input voltage that would turn Qi or Q2 on will 
turn Q4 off and never reach Qi. 
Two zener diodes are connected to each input line 
to protect the sWitches from overvoltage due to surges, 
noise spikes, or accidentally applied power inputs in 
excess of ratings.
Note: 
Requests for further information may be directed to 
Technology Utilization Officer 
Headquarters 
National Aeronautics and 
Space Administration 
Washington, D.C. 20546 
Reference: TSP70- 10022 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546 
Source: R. L. Magee and L. E. Trowbridge of
General Electric Co.

under contract to

NASA Headquarters
(HQN- 10488) 
Brief 70-10022	 Category 01


Solid state switch provides high input-to-output isolation

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