A signal conditioning circuit is described including operational amplifier, a variable source of offset potential, and four resistive impedance. The circuit has constant input impedance independent of gain and offset adjustments. Gain change is effected by varying one of the impedances in an amplifier feedback circuit; offset adjustment is effected through variation of the offset potential source

Holland, V. B.

English

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ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, 'O.C. 20546
APR 3 1975
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Counsel for Patent Matters '
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In accordance with the procedures agreed upon by Code GP
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U.S. Patent No.
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NASA Patent case No.
NOTE - If this patent covers an invention made by a cor
employee of a NASA Contractor, the following is applicable:
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Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19750011446 2020-03-19T20:50:12+00:00Z
United States Patent
Holland
[in 3,872,395
145] Mar. 18, 1975
[54] SIGNAL CONDITIONING CIRCUIT
Arr A K A I Ua
3,030.022
3,082,381
3.518.563
4/1962
3/1963
6/1970
Gittleman
Morrill et al
Ainsworth
23VI95
330/86 X
330/86 X[75] Inventor: Yard B. Holland, San Jose, Calif.
[73] Assignee: The United States of America as
represented by the National
Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: May 5, 1971
[ 2 1 ] Appl. No.: 140,439
[52] U.S. Cl 330/86, 330/69
[51] Int. Cl H03f 1/36
[58] Field of Search 330/86
[56] References Cited
UNITED STATES PATENTS
2.307,308 1/1943 Sorenscn 330/86
2.790.945 4/1957 Chope 330/86 X
Primary Examiner—Nathan Kaufman
Attorney, Agent, or Firm—Darrell G. Brekke; Armand
G. Morin, ST.; John R. Manning
[57] ABSTRACT
A signal conditioning circuit including an operational
amplifier, a variable source of offset potential and four
resistive impedances operatively associated in such a
manner that the circuit has constant input impedance
independent of gain and offset adjustments. Gain
change is effected by varying one of the impedances in
an amplifier feedback circuit and offset adjustment is
effected through variation of the offset potential
source.
2 Claims, 1 Drawing Figure
22*
'OFFSET
10 -= ?1 16
'
IN1 ///
^K/V-H-^
18
eOUT
PATENTEO«ARl8 i f l75 3,872,395
R2
•AA/V
'OFFSET
10 "=r
f
e,
leOUTi
INVENTOR.
VARD B. HOLLAND
BY
ATTORNEY
3,872,395
1 2
SIGNAL CONDITIONING CIRCUIT APPARATUS the present invention includes a pair of input terminals
„ The invention described herein was made by an em- 10 and 11; a pair of output terminals 12 and 13; an op-
ployee of the United States Government and may be erational amplifier 14 having a pair of input terminals
manufactured and used by or for the Government for 16 and 18, and an output terminal 20; three fixed-value
governmental purposes without the payment of any 5 resistive impedances R,, R2 and R3; a variable resistive
royalties thereon or therefor. impedance R4; and a variable source 22 of offset poten-
BACKGROUND OF THE INVENTION tiaL Althou8h the rcsistive impedances R,-R4 are illus-BACK.UKOUNU Oh 1 Ht INVtN I IUN
 in schematic form as ordinary resistors, it is to be
1. Field of the Invention understood that they could likewise be formed of bi-
The present invention relates generally to electronic 10 polar transistors, field-effect transistors, or any other
signal handling apparatus and, more particularly, to a type of circuit element which exhibits a fixed or con-
novel signal conditioning circuit having independent trollable resistive impedance.
gain and offset characteristics and requiring but a sin- The negative input terminal 16 of operational ampli-
gle operational amplifier. fier 14 is coupled to input terminal 10 through the fix-
2. Description of the Prior Art 15 ed-value resistive impedance R! and the positive input
In modern electronic equipment, it is oftentimes de- terminal 18 is coupled to circuit ground. The fixed-
sirable to provide a means for amplifying or changing value resistive impedance R3 and the variable resistive
the offset of incoming electrical signals so as to make impedance R, are connected in series between ampli-
the signals compatible with date acquisition systems, fier input terminal 16 and amplifier output terminal 20
and the like, or to make the signals appropriate for dis- 20 to provide a gain controlling feedback path for ampli-
playing on analog and recording devices. Such condi- fier 14. Fixed-value resistive impedance R2 couples the
tioning circuits should have, among other features, positive terminal of variable potential source 22 to
constant input impedance, linear gain adjustment, and feedback circuit point 24.
independent gain and offset characteristics. Hereto- The circuit functions according to the following
fore, prior art circuits which have provided constant 25 equation:
input impedance have typically had offset and gain _
characteristics which were not independently adjust- e°<" ~ -l«4(«2+«3/Ki «2) + «3/«i \eln - K3/K2 ealtKt
able. In those circuits which did provide independent As indicated by this expression, the output signal eou, is
adjustment of gain and offset, the input impedance was comprised of two independent and algebraically added
not constant; and in those circuits which did have inde- 30 signal components. The first signal component includes
pendent gain and offset as well as constant input im- the input signal ein multiplied by a gain control term in-
pedance, at least two amplifiers were required. eluding the variable resistance R4 which indicates that
SUMMARY OF THE PRESENT ,NVENT,ON £
It is therefore a primary object of the present inven- 3^ offset potential eoffse, which, depending upon the value
tion to provide a novel signal conditioning circuit using of potential source 22, is either added to or subtracted
a single amplifier which has linear, independent gain from the first component and thereby permits offset ad-
and offset, as well as constant input impedance charac- justment of the combined output signal. This expres-
teristics. sion clearly indicates that adjustment of the gain does
In accordance with the present invention, a signal 40 not in any way affect the offset, nor does adjustment of
conditioning circuit is provided including a single oper- the offset in any way affect the gain. The gain is adjust-
ational amplifier, a variable source of offset potential, able from a minimum value of Ra/R4 to a maximum
and four resistive impedances operatively associated in value imposed by the limitations of the amplifier circuit
such a manner that the circuit has constant input im- and is a linear function of the value of impedance R4.
pedance independent of gain and offset adjustments. Adjustment of offset is, of course, also a linear function
One of the resistive impedances is variable from zero of the offset voltage eofftfl.
to some maximum value and is included in a feedback The only material limitations in the application of the
circuit of the amplifier so as to enable gain changes to present invention are imposed by the component accu-
be made. The variable offset potential source is con- racy and the limitations of the operational amplifier.
nected into the feedback circuit in a manner as to en- Any type of operational amplifier will be suitable if its
able the offset to be linearly adjusted without affecting operational parameters are commensurate with the ac-
the circuit gain. curacy and range required.
The several advantages of the present invention will As a possible alternative to the illustrated circuit, the
undoubtedly become apparent to those skilled in the analog input potential ein could be replaced by a cur-
art after having read the following detailed disclosure rent source with R, removed and the circuit would still
of a preferred embodiment which is illustrated in the have the same characteristics. Similarly, the variable
single FIGURE of the drawing. potential source 22 could also be replaced by a current
IM THP r»RAWiNir source with R2 removed from the circuit.
IN THE DRAWING Among the advantages of the present invention are
The single FIGURE of the drawing is a schematic dia- that reduced power is required because only one opera-
gram of a signal conditioning circuit in accordance with tional amplifier is utilized; the circuit has constant
the present invention. input impedance; and adjustment of gain and offset are
DETAILED DESCRIPTION OF THE PREFERRED «*$^  ^^modifications of the present inven-
EMBODIMENT
 tion wi,, undoubtedly become apparent to those skilled
Referring now to the drawing, a preferred embodi- in the art after having read the above disclosure of the
ment of a signal conditioning circuit in accordance with preferred embodiment, it is to be understood that this
3,872,395
disclosure is for purposes of illustration only. Accord-
ingly, it is intended that the appended claims be inter-
preted as covering all modifications which fall within
the true spirit and scope of the invention.
What is claimed is: 5
1. A signal conditioning circuit with a constant imput
impedance and variable gain and offset comprising:
first and second input terminals;
first and second output terminals;
an operational amplifier with first and second inputs 10
and an output;
said second input terminal, said second amplifier
input and said second output terminal being com-
monly connected;
a resistor coupled between said first input terminal 15
and said first amplifier input;
said amplifier output being coupled to said first out-
put terminal;
means coupled between said amplifier output and
said amplifier input for feeding back a signal, said 20
feedback means including a variable resistance and
a variable potential;
the gain of said signal conditioning circuit being a
function of said resistance;
the offset of said signal conditioning circuit being in- 25
dependent of said gain and a function of said po-
tential; and
said input impedance of said signal conditioning cir-
cuit being independent of said gain and said offset.
30
2. A signal conditioning circuit with a constant input
impedance and variable gain and offset comprising: ,,
first and second input terminals;
first and second output terminals;
an operational amplifier with first and second inputs
and an output;
said second input terminal, said second amplifier
input terminal and said second output terminal
being commonly connected;
a resistor coupled between said first input terminal
and said first amplifier input;
said amplifier output being coupled to said first out-
put terminal;
a feedback circuit coupled between said first ampli-
fier input and said amplifier output, said feedback
circuit comprising a resistor connected in series
with a variable resistor;
a variable source of potential;
a resistor coupled between said variable source of po-
tential and the node between said resistors in said
feedback circuit;
the gain of said signal conditioning circuit being a
function of the resistance of said variable resistor;
the offset of said signal conditioning circuit being in-
dependent of said gain and a function of said vari-
able potential; and
said input impedance of said signal conditioning cir-
cuit being independent of said gain and said offset.
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Signal conditioning circuit apparatus

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