Pulse Frequency Modulation(PFMJ is one or the least used ... unlike Bayly, the width or the pulses remains .... Any or the fillers can be selected by means of the.
VOLUME 3. NO. 1, JANUARY, 1991
NUCLEAR SCIENCE AND APPLICATIONS
Pulse Frequency Modulation Based On Biological Systems A. K. M. FAZLUL HOQUE
Atomic Encrg1· Centre P.o. Box no. 164, Ramna. Dhaka, Bangladesh. The usefulness of pulse Frl.!qucncy Mudulation (PFM) in information transmission is ..:mpasizcd. Biological systems al different points of the ') stL'Ill e~pplying the modulating signal. :t)
t\1odulating signal
hJ Integrating w:tvcs (modulated) V u L')
Output waves
or the summer A2 (modulated)
I -\ u
d 1 Tl~c· otil ptil waves
or the comparator A3
I) rvlodulatL'd publ' train
gJ The lkmodtd:llcd wave
Threshold voltage, r=0.5V So, (Modulation dcpth)/(Carricr rate), D=m Jlrf(J=0.4 (Modulating frequency) /(Carrier rate), Q=fm/fo=0.35. The cut ofl frequency or the Lp filter, fc=75 liz. Fig. 8b shows the waveforms for : m 1=6V. 1111 = lOOHz, f0 = 200Hz, r=O. 25V, U=0.12. Q=O 5. lc 0.12= lOOHz. rig. 8c shows the wavcfonns for : m 1=8v. lm=75J-Iz, f0 =167Hz, r=3V, 0=0. 02-+. Q=O. 45, fc=75Hz.
PULSE FREQUENCY MODULATION BASED ON BIOLOGICAL SYSTEMS
(a
l
(b)
the modulating signal with a negligible amount of delay. Also by making an observation of the different waveforms for dillerent values of modulation depth 10 carrier rate ratio and modulating frequency to carrier rate ratio, il may be concluded that the dislottion free information recovery is possible by a low-pass filter from a frequency modulated pulse train, This rephrases what is well known in Neurophysiology, for example, when neural pulse trains arc processed direclly by an averaging filter 12-13.
II is observed in studies of the nervous system that several separate but parallel nerve axons (i. c. information channels) carry, what appears to be the same, information 13 The usc of several rather than one channel in the nervous system leads lO an improvcmem in the signal-todistortion power ratio 16 So the signal-todistortion ratio and the performance of PFM system may be improved by using several channels. When the depth of modulation will he relatively smaller the performance and the signal-to-distortion ratio may he improved by time multiplexing the pulse frequency modulated signals l(H usc in telemetry.
(c) Fig. X
Modulating and demodulating waves
References I.
H. F. Mayer, Principle of pulse Code Modulation Advances in Electronics and ElccLron Ph9sics Academic Press, 3, 24 (1951)
2.
B. Ribkt, Radio Tclcmetcring, Advances in
3.
Electronics, Academic Press, 11, 288 (1951) E. M. dcloraing , Proc. IRE, 37, 702 (June, 1949)
with different modulating depth to carrier rate ratio, D and modulating frequency to carrier rate ratio
Q.
D = 0.4,
Q= 0.35
bJ D = 0.12,
Q = 0.05
c) D =lJ.lJ24
Q = 0.45
a)
4.
5.
D(ookc, Z. Jelonck, A. J. Oxford and E. FiLch, Pulse Coomunication J. lEE (London), vol.94, Pan-IliA, II, 83. (194 7) R. W. Jones. C. C. Li, A U. Meyer, and R. B.
Dicussion
pintc.r, "Pulse Modulation in Physiological systems, Phenomenological aspects, "IRE
From the expcrimcmal results it is seen that Ihc repetition rate of Ihe pulse Irain is varied in accordance with the modulating signal. When the modulated pulse train is passed thmugh a Lowpass filter with a cut orr l'requency equal to the frequency of the ·modulating signal and much lower than the unmodulatcd pulse carrier rate, the out put signal of the Iiller is the same as that of
Trans. Biomedical ElccLronics, Vol. BME-8, 59 (Jan, 1%1). B. Katz Scientific American, 205, 3, 209 (1961 ). E. I. Jury and J. G. Blanchard, Memorandum No. ERL 172, Electronic Research Laboratory, University or California, Berkeley, California (1967).
6. 7.
'
A.KM. FAZLUL HOQUE
14 8.
R. Pcthing, Electronic Conduction 111 Biological systems, Electronics and Power
(lEE, London), 9. 10.
(445,1~
Oct. 1973).
1.>.
C.A. Terzuolo and R.E. Poppclc, Science, 159, 743 (Feb. 16, 196XJ.
14.
A.K. Kamaluddin, Journal of Institution of Engineers (India), 56, Pan ET I, 10, (August, 1975).
15.
B. Vanderpol and J. Vander Mark, Philosophical Magazine, Suppl. 6, 763, ( 192H).
16.
L. Maffei, J. Ncurophysiol. 31 2H3, (M
