Phase-locked-loop phase modulator has the capability of generating a 6.8MHz carrier at modulation indexes as high as 2.5, with a distortion of the demodulated signal of less than 5 percent. These characteristics are obtained without the use of multipliers

Badstiibner, C. G.

English

NASA Technical Reports Server

SOctober 1969	 ,	 Brief 69-10487 
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. 
3.Th-
Phase-Locked-Loop Phase Modulator with High Modulation Index,

Low Distortion 
The circuit schematic shows a phase-locked-loop 
phase modulator that has the capability of generating 
a 6.8M1-lz carrier at modulation indexes as high as 2.5, 
with a distortion of the demodulated signal of less than 
5 percent. These characteristics are obtained without 
the use of multipliers. 
The phase-locked loop consists of Z3, QI, Q2, Z6, 
and Z. The voltage-controlled oscillator, Z3, is asso-
ciated with the frequency-determining voltage-variable 
capacitors CR1, CR2, and variable inductance LI. 
Blocking capacitors C7 and C8 are of sufficiently
large capacitance to prevent detuning of the tank cir-
cuit. Capacitors CR1 and CR2 receive a -12V bias from 
R9. Resistors RIO and RI 1, which are return paths 
for the bias voltage, prevent loading of the tuned cir-
cuit. The output stage of Z3 is an emitter follower 
which is connected to QI to allow capacitive-coupled 
loading at full output swing. Transistor Q2 converts 
the sinusoidal input (2.2 V, p-p) from QI into a 30-
nsec-wide pulse going from +5.5 V to grouhd poten-
tial. (Diode CR3 is used to clamp the flyback at 5.5 V.) 
This pulse is directly coupled from the collector of 
(continued overleaf( 
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Aeronautics and Space Administration. Neither the Uciiteø 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.
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Q2 to pin I of Z6. The latter is a pulse-triggered bin-
ary micrologic integrated circuit (connected to form a 
flip-flop) which serves as the phase detector of the 
phase-locked loop. The reference clock signal (6.8 
MHz) entering Z5 at pins 4 and 5 is divided by 2, so 
that the frequency of the output square wave at pins 2 
and 3 of Z5 is 3.4 MHz. This output is capacitively 
coupled to pins 4 and 5 of Z6, using the negative-going 
edge for triggering. The output of the phase detector, 
Z6, is taken from pins 2 and 3 and fed into a low-pass 
filter network consisting of R18, C14, R17, and C3. 
This filter reduces the 3.4 MHz fundamental frequency 
originating at output pins 2 and 3 of the phase detec-
tor, Z6. Resistors R 1 and R18 also provide a dc return 
for Z2. The output of the low-pass filter feeds into pin 
2, the noninverting side of Z2. The amplified correc-
tion voltage from pin 6 of Z2 is fed back through R23 
toCRI andCR2. 
The modulation signal is injected at JI into the 
noninverting input of ZI at pin 3 (approximately 
20.000 ohm input impedance). With a I V p-p input 
signal at ii, the amplifier (ZI) has a gain of 5; its 
frequency response is flat out to 100 kHz and rises by 
1.0 dB at a frequency of 330 kHz. This amplifier has 
the important function of providing a dc-coupled 
modulating signal to Z2 so that the low frequency 
response of the modulator is unrestricted. The am-
plifier also provides a virtual ground for R5 and 
compensates for the loss of modulation signal through 
this resistor, which furnishes a dc offset voltage at 
pin 2 of Z2. Phase modulation occurs when the modu-
lation signal enters this pin. As Z3 is phase-locked to 
the reference signal at J2, the demodulated signal 
originating at the phase detector (Z6) output cancels 
any changes in frequency of the voltage-controlled 
oscillator (Z3) that would be caused by the amplified 
modulation signal from Z2. This cancellation will occur 
at pin 6 of Z2 and depends on the loop gain and phase 
shift through the loop. As the modulation frequency 
is increased, the signal at this pin increases in lead 
until the first break point of the closed-loop response 
is reached.	 - 
Theoretically, this circuit can have a maximum 
phase deviation of lZj.0° (modulation index of 3.14), 
but in actual practice this deviation is limited by (I) 
the capability of the phase detector, Z6, to produce a 
properly damped, full square wave at the reference 
frequency, and (2) the loss in pulse width of the Z6 
square wave output at the dc switching level of the 
pulse input to pin I of Z6. The large phase deviations 
of this circuit are made possible by the use of Z6, which 
is a digital-type (variable duty cycle) phase detector. 
Values and types of components designated in the 
schematic are listed below. All resistors are rated at
1/4 W; resistance values are given in K ohms unless 
indicated as ohms. Designation of commercial com-
pany products is only indicative, not exclusive, and is 
not a recommendation of one company over another. 
RI, R2 22 
R3, R8, R20 1.5 
R4 82 
R5 -	 10 
R6, R23 3.3 
R7 5.6 
R9 10 (Pot.) 
RIO, RI! 15 
R 1 100 
R13 33 
R14 -	 2.2 ohms 
R15 -	 5 (Pot.) 
R16
-	 68 ohms 
Rl7 8.2 
R18, R19 1.8 
R21	 / -	 180 ohms 
R22 - 
Cl, C4 270 pf (mica) 
C2 18 p 
C3 22 p 
CS 20 p 
C6-CIO, C13, C15 0.022f 
Cli 0.8-18 pf 
C12	 - 39 p 
C14 82 p 
ZI, Z2 Fairchild ya 709 
Z3 RCA CA-3001 
Z4 RCA CA-3005 
Z5, Z6 -	 Fairchild Dtl 950
QI, Q3
	 - 2N 2222 
Q2	 2N 2369 
LI	 Cambion 1505-5 
7.8 - l6H 
L2, L3	 - l0H 
CR1, CR2
	 - TRWvaricap 1N4815B 
CR3	 1N914 
Note: 
This Tech Brief is complete in itself. No additional 
information is available. 
Patent status: 
No patent application is contemplated by NASA.

Source: C. G. Badstiibner of 
Radio Corporation of America
under contract to

Manned Spacecraft Center
(MSC-12247)
. 
.. 
Brief 69-10487	 Category 01 


Phase-locked-loop phase modulator with high modulation index, low distortion

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