Commercially available integrated circuit that is marketed as a digital computer input gate circuit was converted to a linear amplifier in a microphone circuit that has high input impedance, low output impedance, low cost, and is small enough to fit on a standard printed circuit card

Harper, T. P.

English

NASA Technical Reports Server

- 24VDC 
BE 
FIG. 2 
LINEAR AMPLIFIER CONVERSION 
January 1968	 .	 Brief 68-10015 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Input Gate Circuit Converted for Use as Linear Amplifier
Output 
-- 1 
-4----  
2	
Output 
1
Output vinput 
- LHC
Source 
FIG. 1
MOS 3 INPUT GATE CIRCUIT 
Ground 8 
Input 
Input 2.__.4j 
Input 5q 
input NAND gate circuit. The gate contains three 
MOS transistors in series. Figure 2 shows the same 
circuit biased and converted for linear operation. Be-
cause the source and drain of the MOS are inter-
changeable, the common connection may function as 
a source in one pair and a drain in another pair. By 
connecting pin 2 to the —24 vdc supply, pin 3 to source 
diode Di, pin 4 to pin 7, and the remaining pins to 
suitable bias points, the circuit is converted. An ac 
input is coupled through capacitors C l
 and C2 and is 
applied to the gate elements of MOS A and B. The 
MOS A and B circuit forms a differential amplifier 
controlling the gate of MOS C which controls the 
output signal across R5. 
Voltage dividers RI and R2 provide dc bias for 
How it's done:	 MOS A. Constant current diode Di supplies a con-
Figure I shows a commercially available integrated 	 stant 2-milliampere current to the source elements of 
circuit, which is a P-channel enhancement type, three- 	 MOS A and B. Thus a constant total drain current 
(continued overleaf) 
The problem: 
To design a linear amplifier in a microphone circuit 
that has high input impedance, low output impedance, 
low cost, and is small enough to fit on a standard 
printed circuit card. Existing techniques use several 
components and voltage feedback circuitry for im-
pedance matching. These techniques usually require 
expensive and bulky components. 
The solution: 
Convert a commercially available integrated circuit 
that is marketed as a digital computer input gate cir-
cuit. This integrated circuit uses metal oxide semicon-
ductor (MOS) devices, and is reconnected as a linear 
amplifier.
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=19680000015 2020-03-12T05:42:39+00:00Z
flows regardless of signal polarity. MOS A or B is en-
hanced whenever a negative voltage is applied to its 
gate. The electrostatic field produced by the gate volt-
age is applied to the source and drain junctions form-
ing a continuous current path. The magnitude of the 
gate signal determines the degree of enhancement, 
which in turn determines conductivity. 
Constant current diode D2 supplies a constant 
1-milliampere current with a high impedance load to 
the drain element of MOS B. The diode combination 
establishes circuit balance regardless of temperature 
effects to circuit parameters and overcomes the prob-
lem of transconductance mismatch. Thevalues of volt-
age divider resistors Ri and R2 and resistors R3 and 
R4 are selected for balance of the high input imped-
ance ratios which are necessary for MOS circuit oper-
ation. As MOS A and B vary in conduction, the am-
plified signal is applied to the gate elements of MOS 
C. As MOS C conducts, a low impedance output 
signal (3000 ohms) is developed across resistor R5.
Thus, an overall circuit impedance transformation 
from 10 megohms to 3 kilohms is provided. 
The voltage gain of the circuit is linear over a fre-
quency range of 4 Hz to 100 kHz. Above 100 kHz, the 
voltage gain decreases and is reduced by a half at ap-
proximately 180 kHz. 
Note: 
Inquiries concerning this circuit may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10015 
Patent status: 
No patent action is contemplated by NASA. 
Source: T. P. Harper 
of IBM 
under contract to 
Marshall Space Flight Center 
(M FS- 14265)
S 
Brief 68-10015	 Category 01


Input gate circuit converted for use as linear amplifier

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server