Wideband voltage controlled oscillator with high phase stabilit

Hearn, C. P.

English

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NATIONAL AERONAUTICS AND SPACE 
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https://ntrs.nasa.gov/search.jsp?R=19710017795 2020-03-17T03:12:38+00:00Z
Patented March 9, 1971 
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United States Patent f 1  3,569,866 
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[72] Inventor Chase P. Heam 
Williarnsburg, Va. 
[2 1 ] Appl. No. 779,024 
[22] Filed Nov. 26,1968 
[45] Patented Mar. 9, I971 
[73] Assignee The United States of America, as 
represented by the Adminrktrator of the 
Nationd Aeronmaanties a~nd Space 
Administratiun 
[561 References Cited 
UNITED STATES PAT:EI\;TS 
..................... 3,068,427 1211962 Weinberg 332 i30  
..................... 3,276,032 911966 Ordower 3 3 1 / i S 3  
3,321,715 511967 Bloch ...................... 331;15 
Primary Excrminer-John Korninski 
Alrorneys-Howard J Qsborn, William B$ King '2nd G T 
McCoy 
ABSTRACT: This disclosure describes a widcband voltage 
controlled oscillator with high phase stability. A resonator 
I541  WIDEBAND VCO WITH HIGH PHASE 
consisting of a number of identical L-C resonators reactively 
STABILITY coupled to the input and the output of a highly phase stable 
amplifier is described. The resonant frequency of each aesona- 3 Claims, 1 Drawing Fig. tor is controPled by applying a modulai:ing sigaral to voltage [521 U.S. @I ........................................................ 331l117, variable ca~acitors which form a norlion of the resonators. In 
33 11109.33 111 77,332130 additiofi, the amplifier has electrically-vi~riable negative feed- 
[51 ]  Ent. CI ......................................................... H03b 5/12 back which improves its phase stability and simulinneousiy 
[5Q] Field of Search ............................................ 33 1/36 (C), provides a means for maintaining phi: oscillations nearly 
177 (V).  1 P 7, 109, 183; 332130 (V) sinusoidal. 
I-S-TABcE- - - - - - - - - - - -  - - - - - - - - -  
D I-  D 2 I 
L FEEDBACK 
; AMPLIFIER ;/" 
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MODULATION 
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3,569,866 
1 2 
ble capacitors, the resonant clrcults are reactivei: coupled 
WIDEBAND VCO WITH HIGH PHASE STABILITY together and reactively coupled to the Input ar,d the output of 
the highly phase stable amplifier The resonant frequency of 
BACKGROUND OF THE INVENTION each resonator circuit IS varied by ag~piytng a modulating 
The need for and the use of an oscillator that generates to the 
highly subilized oscillations that are electrically variable over In accordance with another principle of this invention, the 
a wide range is well known, The prior art has attempted to electrically variable negative feedback portion of the highly 
provide such an oscillator; however, the apparatus resulting phase stable amplifier includes means far developing a DC 
from such attempts has not been entirely satisfactory. voltage proportional to the oscillator ou1:pue voltage level. The 
~h~ phase of any is dependent upon the DC voltage is applied to a voltage-variable negative feedback 
of the oscillators resonant components to correct for network consisting of semiconductor diodes which function as 
random phase perturbations occurring within the oscillators resistance elements. 
feedback loop. now a particular resonator can correct for In accordance with yet another principle of this invention, 
phase perturbations external to the resonator can be deter- 15 the modulating signal is applied to coupled pairs of resonant 
mined by measuring the resonator-s normalized rate-of- circuits by low pass filter sections whose cutoff frequency is 
change of phase with respect to frequency. The "stability fac- greater than the highestm~dulatingfrequenc~. 
tor'' obtainable with a simple L-C resonator is limited by the It will be appreciated from the foregoing summary 3fBhe in- 
loaded Q of the resonator. That is, the stability factor is equal vention that a wideband highly phase stable oscillator is pra- 
to twice the Q of the resonator circuit, And, it is well known 20 vided. The oscillator is formed of conventional components 
that Q's above 300 are difficult, if not impossible, to obtain and, hence. it is inexpensive to manufacture. In addihion the 
with lumped L-C componens. Hence, conventional L-C components making up the invention are c~nnected in un- 
tuned oscillators are limited in stability because of the limits complex fashion. It will also be appreciated that eEectrica%ly 
placed on the lumped components that make up the resonator variable negative feedback gain control circuit results in 
portion of the oscillator circuit. This result remains true even 25 nearly linear operation and stabilizes thit phase characteristic 
though the L-C components are electrically variable. of the amplifier with respect to fluctuations in ambient tern- 
Oscillators having extremely high stability factors using perature and supply voltages. The mulrisection resonator ex- 
piezoelectric crystals have been developed by the prior art; hibits a stability factor greater than tha:t of any one section; 
however, the frequency range over which a crystal controlled hence, it can correct for a loop phase perturbation with a 
oscillator can be modulated is quite limited-typically less 30 smallerfrequency perturbation. 
than . 1  percent of the center frequency. 
"Reactance Tube" modulators are another form of oscilla- BRIEF DESCRIPTION OF THE DRAWING 
tor that has been developed by the prior art. This type of oscil- The foregoing objects and many of ad- lator is capable of somewhat wider frequency deviation than a vantages of this invention beconle more ap- piezoelectric crystal controlled oscillator; however, it suffers 35 preciated as the same becomes 
un,derstood i?:I reference from an added problem. Specifically, these oscillators include to the following description when taken in con;;imric- 
an active element in shunt with the resonator circuit which in- tion with the accompanying drawing wherein a em- troduces a source of phase instability into the overall oscillator bodiment of the invention is 
svstem. 
a A more sophisticated prior art apparatus for.frequency sta- 40 DESCRIPTION OF THE PREFERRED E M B O D ~ ~ ~ J ~ E N T  
bilization uses a frequency modulated oscillator phase-locked 
to a highly stable fixed frequency oscillator source. The prima- The FIGURE illustrates a preferred embodiment of the in- 
. - 
ry dis&jvintages of this system are: the center frequency of vention and comprises a stable feedback arnpiifie?. section I I 
the oscillator is not variable, and, there is a lower limit on the and a resonator section 13. The stable feedback amplifier sec- 
modulating freauencv which limits the deviation rate to 45 tion 11 comprises first and second amplifiers designated Al 
A * 
somethinggreater than the phase-locked loop bandwidth. and A2; first second and third diodes designated 61, $2 and 
In summary, frequency modulated oscillatois using single L- D3; a first capacitor designated C1; :and, a first inductor 
C resonators with electrically variable reactance elements or designated L1. The first amplifier has a control iripui and the 
"Reactance Tube" oscillators are, both fundamentally limited first inductor L l  has a variable tap. 
in their ability to generate highly phase stable oscillations. 50 The output from A l  is connected to the input of ."i and the 
Highly phase stable crystal oscillators are incapable of wide- output of A2 is connected through &I 813 ground. The output 
band frequency deviation. Phase-locked loop stabilized oscil- of A2 is also connected to the anode of 612. The cathode of D2 
lators have a lower rate limit beyond which they cannot be is' connected to the- anode of D l .  The cathode of Dl is con- 
deviated. In addition, the center frequency of phase-locked 55 nected to the anode of D3 and to the control input oFAl. The 
loop stabilized oscillators cannot be varied electrically. cathode of D3 is connected to the tap of 1.1. CB is connected 
Hence, prior art oscillators do not provide stable wideband between the anode of D l  and the cathode of D3. Preferably, 
oscillators. D l  and D2 and D3 are high-frequency point-contact diodes. 
Therefore, it is an object of this invention to provide a wide- By the foregoing connection, D2 and C6 deve'xops a DC 
band voitage controlled oscillator having high phase stabiiity. 60 voltage proportional to the oscillator ooliput level. This volt- 
Yt is also an object of this invention to provide a wideband age is applied to D l  and D3 which are in series to t l ~ e  control 
voltage controlled oscillator having high phase stability that is current input of A l  and in parallel to the output voltage 06. the 
electrically uncomplicated, and, therefore, inexpensive to oscillator. When the output level increases. the dynamic re- 
manufacture. . 
' sistance of D l  and D3 reduces. The redlrcrion ir? the dynzrnic 
It is still a further object of this invention to provide a new 65 resistance of and ~ ) 3  increases the amount of 
and improved voltage controlled oscillator having high phase feedback, thereby establishing a new operating giais: for ti.le 
stability over a wideband that uses conventional components. tandem amDlifiers, 
SUMMARY OF THE INVENTION It will be appreciated by those skilled n i l  the art that negatlve feedback is used around the ampllfierf no ~ r a v ~ d e c  certain 
In accordance with a principle of this invention, a wideband 70 desired results. First, negative feedback tex~ds to make the 
voltage controlled oscillator having high phase stability is pro- transfer characteristic of the circuit independent of the pro- 
vided. The invention consists of two basic subsystems: ( 1 )  a perties of the active elements contain~:d in the amplifiers. 
highly phase stable amplifier with electrically variable nega- Second, the ratio of closed loop phase instability to cpen loop 
tive feedback; and ( 2 )  a resonator circuit consisting of a phase instability is reduced in direct proportion to the amount 
number of identical .L-C resonators tuned with voltage varia- 75 of negative feedback. Third, negative P s,cdback furnishes an 
3,569,866 
3 4 
amplifier gain so that oscillations vention can be practiced otherwise than as specifically 
amount of negative feedback is easi- described herein. 
, because they are connected so that I claim: 
1. A wideband voltage controlled oscilEator with high phase 
5 stability comprising: 
a stable feedback ampfifier having variabie negative feed- 
back for high phase stability: 
first and second voltage tuned resonators for controlling the 
frequency of osciliatiosl coupled between the input and 
10 the output ofsaid feedback amplifier; 
said first voltage tuned resonator including a first capacitor 
riahie capacitors designated a first inductor and a first voltage variable capacitor con- 
led through C3 in series with nected in series with said first capacitor connected to the 
input of said feedback amplifier; 
15 said second voltage tuned resonator including a second 
capacitor, a second is~ductor and a second voltage varia- 
bie capacitor connected in series with said second capaci- 
tor connected to the output of said feedback amplifier 
and wirh said second voltage variable capacitor con- 
20 nected to said first voltage variable capacitor; 
first bias means connected to ihe junction of said first 
capacitor and said Erst inductor; 
second bias means connected to the junction of said second 
capacitor and said second inductor; and 
2 j means for connecting a modulation source to said first and 
second voltage tuned resonators, said means including a 
third inductor connected between said modulation source 
cv pass filzer herein descr!brd. and the junction of said first and second voltage variabie 
capacitors, a first resistor and a third capacitor connected 
30 in parallel between the junction of said first and second 
voltage variable capacitors and ground, and a fourth 
capacitor connected between said modulation source and 
ground. 
2. A wideband voltage controlled oscillator with high phase 
3 j stability as claimed in claim 1, wherein said stable feedback 
amplifier comprises: 
a controllable first amplifier having its input connected to 
the prior art would said first capacitor; 
,lation directly to ~ 5 ;  a second amplifier having its input connected to the output 
40 of said Grst amplifier; 
a fourth inductor having a tap, said intiiicto: connected 
between the output of said seco:ad arnpiifier and ground, 
the tap of said inductor connected to said second capaci- 
tor; 
45 a first diode havdag l?s cathode connected to :he tap of said 
fourth inductor and its anode connected :o ?he contrc': 
input of said co7trollaSle first amp:lfier; 
a second diode; 
s between the a third diode; said secolc' and third diodes connected in se- 
50 ries so ?hat the ccithole ohald  second diode Is connected 
to the colztro? inr;ut of said co~trollable first amplifier and 
the anode of said third a ~ o d e  is connected to the output 
foregoing description of the ofsaid second amplifier; and 
ccomplicated apparatus for a fifth capacitor connected between the junction of said 
llations over a *ide band- 55 second and third diodes and the cathode of said first 
the modulation signal, the diode. 
olied. by con- 3. A wideband voltage controlled osciPlator with high phase 
he stability of the amplifiers comprising: 
tor is achieved. In summary, controilabie amplifier means; 
arj,b~e feedback to 60 an inductor having a tap connected to the output of said am- 
mbei of reactively coupled plifier means; 
obtain high stability, and a first and second diodes connected in series between the out- 
e variable frequency resona- put and the control input of said ampiifier means; 
a third diode connected between the conbro! input of said 
ing description 45 amplifier means and said tap; 
ention and that a capacitor connected between said tap and the junction of 
said first an2 second diodes; and 
a multisection, voltage-tuned resoator br conlrolling the 
Frequency of usci?!atlor at said ta? conriected E7er.wecn 
. . 
70 saaic tap and :he input :a said anpli5,er means. 


Wideband VCO with high phase stability Patent

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