Frequency control circuit of FM modulator

Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Frequency or repetition rate conversion or control

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327100, 327101, 327129, 327407, 332135, 331113R, 331177R, 331179, 341144, H03B 2100, H03K 3282

Patent

active

055857515

ABSTRACT:
A frequency control circuit of an FM modulator with a small number of external parts and a low number of IC pins, including a non-linear D/A converter, a current generator circuit and an emitter-coupled multivibrator. The non-linear D/A converter for giving an analog optimum resistance value depending on digital frequency control signals includes a plurality of resistors weighted by K.sup.n (1<K<2 and n is a sequential natural number). The current generator generates a current .DELTA.I depending on the output resistance value of the non-linear D/A converter. An oscillating frequency of the multivibrator is determined in proportional to I.sub.o /4CF.DELTA.I (I.sub.o represents a current value of an operational current source, C represents a capacitance of a capacitor, R represents a resistance value of a resistor and .DELTA.I represents a current flowing in the resistor). When the oscillating frequency is controlled depending on .DELTA.I, a value of a frequency deviation can be changed almost linearly to readily carry out the control.

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Kato, Kazuo, et. al., "A Low-Power 128-MHz VCO for Monolithic PLL IC's", I.E.E.E. Journal of Solid-State Circuits, vol. 23. No. 2, Apr. 1988, N.Y., pp. 474-479.
IBM Technical Disclosure Bulletin, "Voltage Controlled Oscillator Frequency Switch", vol. 31, No. 5, Oct. 1988, N.Y., p. 235.

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