Commutator device combines several individual signal-input lines into single output line. Its desirable characteristics are - low input impedances, high output impedance, very high forward-to-reverse transmission ratios, and minimal gating spike coupling to either the inputs or the output

Farnsworth, D. L.

English

NASA Technical Reports Server

June 1971	 Brief 71-10148 
NASA TECH BRIEF 
Marshall Space Flight Center 
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 National Technical Information 
Service, Springfield; Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Isolated-Line Commutator-Amplifier 
A commutator device with nearly ideal charac-
teristics combines several individual signal-input lines 
into a single output line. Originally designed for solid 
state imaging mosaics, the commutator may be easily
Figure 1, a block diagram of the isolated-line 
commutator, shows the primary novelty of the device; 
i.e., the use of unity-gain, impedance-transforming 
amplifiers in each signal line, as opposed to in-
Signal	 Load Line Sw itches Line Amp s 
Inputs	 Resistors Ron
-high 
•	 R1
low : R0ff
Gate -
Summing 
Zhjgh Amplifier 
Output 
.	
R2
VGate
ZIOW 
.
.
1Zhigh 
ZIQW 
Ron Zhigh 
Rifln
Ilow E ff 
Gate
. Gate Signal 
Generator	 •
Figure 1. Block Diagram of Commutator 
modified to suit any situation in which several 
low-level signals must be merged into one output. 
Among its desirable characteristics are: low input im-
pedances, high output impedance, very high forward-
to-reverse transmission ratios, and minimal gating 
spike coupling to either the inputs or the output. 
Multiple signal inputs can be connected to the output 
sequentially by successive gating, or simultaneously 
by algebraic summing, and the input lines will re-
main essentially uncoupled. The commutator also has 
high resistance to nonselected inputs and very low 
noise generation, characteristics which are required 
for applications involving very weak signals.
dividual load resistors used in prior designs with 
only limited success. The line loads are the re-
sistors Rin, located at the input to reduce the effect 
of variable forward switch conductance (R on ) so that 
all input lines see the same load. Since each switch 
output is fed into the very low input impedance of 
the unity-gain line amplifiers, the conductance of all 
switches is independent of the input signal level. 
The forward-to-reverse transmission ratio is further 
maximized by the amplifiers. 
Figure 2 shows the circuit configuration used in 
the existing commutator design. Circuit details may 
be modified to suit the requirements of a given 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned-rights. 
https://ntrs.nasa.gov/search.jsp?R=19710000147 2020-03-17T02:23:59+00:00Z
. 
V 
-
Output 
 i 
Figure 2.	 Schematic of Commutator 
application. Metal oxide semiconductor (MOS) devices verted to respond to negative-going signals by in-
are	 used	 in	 the	 line	 switches to obtain	 low levels verting	 all	 supply	 voltages	 and	 replacing	 n-type 
of gate-to-signal-line leakage and spiking interaction, devices with p-types, and vice versa. 
These components exhibit essentially no dc gate leak- Notes: 
age, and the circuit arrangement makes symmetrical 1. Since	 nearly all	 of the circuitry associated 	 with 
switching spikes available through each device. These
the	 commutator	 consists	 of	 active,	 solid	 state 
may then	 be effectively cancelled at the summing devices, the innovation should lend itself readily point if the signal inputs are gated in a continuous to MSI or LSI techniques. 
sequence	 with	 no	 time	 lapse	 between	 selection 2. Requests for further information may be directed periods. If dead intervals are to exist between gates, 
the circuit may be modified to use complementary to: Technology Utilization Officer devices	 in	 each	 switch,	 so	 that	 spike	 cancellation Code A&TS-TU 
will occur at the input to the individual line ampli- Marshall Space Flight Center 
fiers. Huntsville, Alabama 35812 
The common-base line amplifiers were, selected be- Reference: B71-10148 
cause of their very low input impedances and be-
cause their emitters never rise more than one diode Patent status: 
drop above the base reference voltage. By referenc- Inquiries about obtaining rights for the commercial 
ing the	 bases one diode drop	 below ground, the use of this invention may be made to: 
emitters	 are	 essentially	 held	 at	 ground	 potential. Patent Counsel 
This	 configuration	 holds	 the	 source	 leads	 of	 the Mail Code A&TS-PAT 
MOS switches at a constant voltage and allows full George C. Marshall Space Flight Center 
use of the switching device characteristics for any Marshall Space Flight Center, Alabama 35812 
particular gating-signal level. Source: D. L. Farnsworth of With	 the	 circuitry	 shown,	 the commutator will Westinghouse Electric Corp. 
respond	 to	 positive-going	 input	 signals	 only.	 The
under contract to lower voltage limit may be modified by changing the Marshall Space Flight Center base reference voltage, or the system may be con- (MFS-20734)
Brief 71-10148	 Category 02 


Isolated-line commutator-amplifier

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