| 摘要 |
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 Kn (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 Io/4CF DELTA I (Io 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.
|
