Two or more tandem amplifier stages, one of which is tuned, added to a circuit permit tuning an oscillator over frequency range of six decades. Oscillator operates in distributed mode for increased frequency stability. Within practical limitations, stability increases by increasing number of tuned stages

Rippy, R. R.

English

NASA Technical Reports Server

August 1971
	 Brief 71-10286 
NASA TECH BRIEF 
Goddard 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 
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be directed to the Technology Utilization Off i ce, NASA, Code KT, Washington, D.. 20546. 
Oscillator with Wide Dynamic Tuning Range 
The problem: 
Tune an oscillator over a frequency range of six 
decades by changing only two circuit components. 
The oscillator may operate in a distributed mode for 
increased frequency stability.
Li = 1.1/tH 
Ci 920pffor 
B+	 5 MHz output
p 
15 V
I	 Rd 
Li	 ci_L	 510 5MHz 
Output 
2.2sf	
-i }-o I 1C2	 2.2zf Ii 
2.2 u  
El
01	
02 
10K	 470	 IMEG 
p 
CM	 Resonant Drain Oscillator 
The solution: 
Use two or more tandem amplifier stages, at 
least one of which is tuned. Remove the feedback 
voltage from the drain of the last stage and apply 
it to the gate of the first stage to eliminate the need 
for frequency sensitive impedance matching circuitry. 
Within practical limitations, the stability can be in-
creased by increasing the number of tuned stages. 
How it's done: 
The basic oscillator circuit (see fig.) consists of 
a two-stage non-inverting amplifier with the output
terminal connected to the input through C2. Qi 
functions as a selective amplifier which controls 
the frequency and stability of the oscillator; Q2 
is a wideband amplifier and phase inverter that 
provides positive feedback to Qi at the resonant 
frequency of Li-Cl. The circuit oscillates at the 
frequency for which the phase shift through the 
amplifier is zero, provided that the gain of the ampli-
fier is equal to or greater than unity. This frequency 
can be tuned by varying the component values of Ll-
Cl in the drain circuit of Qi. Oscillations over a 15:1 
range can be achieved by varying only Cl, and a 
10 6:1 range can be obtained by varying both Li and 
Cl. The wide frequency span which can be covered 
by varying only one component makes the circuit 
a logical choice as a voltage controlled oscillator. 
Hyperabrupt varactors are available with a capacity 
range as high as 20:1. Since the frequency of oscil-
lation is inversely proportional to the square root 
of capacity, these devices should make it possible 
to construct voltage controlled oscillators with greater 
than a 4:1 frequency range. 
For applications primarily concerned with ob-
taining maximum frequency stability, Q2 can also be 
operated as a selective amplifier by replacing Rd with 
an LC circuit identical to Ll-Cl. If n independent 
tuned stages are used, the oscillator will have a 
I igure of merit F given by: 
1^ J 
1/2 
T11 
where Tn is the group delay of the nth stage, on 
is the RMS phase jitter of the nth stage, and f() 
I Coil lililied 01 crIcii) 
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=19710000285 2020-03-17T02:20:39+00:00Z
is the frequency of oscillation. The smaller the F, 
the greater the stability. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: B71-10286
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 204 
Goddard Space Flight Center 
Greenbelt, Maryland 20771
Source: R. R. Rippy

Goddard Space Flight Center

(G SC- 1108 6) 
Brief 71-10286	 Category 01


Oscillator with wide dynamic tuning range

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