Active RC network is capable of extremely high Q performance with exceptional stability and has independently adjustable zeros and poles. The circuit consists of two integrators and two summers that are interconnected to produce a complete second-order numerator and a second-order denominator

Huelsman, L. P.

Kerwin, W. J.

Newcomb, R. W.

English

NASA Technical Reports Server

June 1968	 Brief 68-1021Q. 
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. 
Active RC Networks of Low Sensitivity for Integrated
Circuit Transfer Function Synthesis 
The lack of suitable inductive components for 
integrated circuit construction requires that other 
techniques be developed. Most methods of active RC 
filter synthesis are unsuited to high Q performance 
due to the7 extreme system sensitivity to change in the 
passive or the active components. 
The network configuration shown is capable of 
extremely high Q performance with exceptional stabil-
ity (insensitivity). In addition, the zeros and poles are 
independently adjustable. (The zeros may be located 
anywhere in the complex frequency plane and the 
poles anywhere in the left half-plane.) This network 
produces 2 poles and 2 finite zeros that can be ar-
ranged to produce a second order low pass, high pass, 
or bandpass function as desired. In addition, all func-
tions are available simultaneously. Higher order func-
tions are obtained by direct cascade connection of 
these building blocks. The frequency of maximum 
response and the Q are adjustable using a single 
resistor, R for frequency adjustment, then a second 
resistor R2 for Q adjustment. 
The circuit consists of two integrators and two 
summers that are interconnected to produce a com-
plete second-order numerator and a second-order 
denominator. 
Calculation and experiment show that the system 
is extremely insensitive to changes in both the active 
and passive components. 
To place the zeros in the right half-plane, the signal 
from the first integrator, Ki, is inverted. The output 
(continued overleaf) 
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.
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summer K0, can then be eliminated as all inputs to it 
have the same polarity; however, it is convenient to 
use the output summer for isolation. 
The sum of the sensitivities to the first four resistors, 
R, Ri, R2, R3 is zero, and all sensitivities are inde-
pendent of Q. The sensitivity to changes in R8 and C  
will be zero if the R8CI product remains fixed, as will 
the frequency sensitivity. In addition, the frequency 
sensitivity to R9 and C2 will be zero if the R9C2 
product is held constant. 
Note: 
Complete details of this circuit are contained in: 
State-Variable Synthesis for Insensitive Integrated
Circuit Transfer Functions, by W. J. Kerwin, L. P. 
Huelsman, and R. W. Newcomb, Solid State Circuits 
Journal of the IEEE, September 1967. Copies of this 
article are available from: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B68-10210 
Patent status: 
No patent action is contemplated by NASA. 
• Source: W. J. Kerwin, L. P. Huelsman, 
and R. W. Newcomb 
(ARC-10146) 
Brief 68-10210	 •	 •	 Category 01


Active rc networks of low sensitivity for integrated circuit transfer function

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