| 摘要 |
PURPOSE:To control stably the modulation factor of an FSK modulating circuit by producing a control signal in response to the difference between two output frequencies of a phase locked loop corresponding to a binary level, and controlling the level of an input signal. CONSTITUTION:An input signal A transmitted through an LPF1 is applied to a variable attenuator 13 which is controlled by a control signal produced from a control circuit 14 in terms of the attenuation quantity. Then a voltage controlled oscillator 4 is controlled via a buffer 3. The output B of the oscillator 4 is supplied to gates 15 and 16, and gate outputs C and D of binary levels are supplied to carrier reproducers 17 and 18 respectively. Then the outputs E and F of the reproducers 17 and 18 are supplied to a mixer 19, and a signal having a frequency equal to the difference between both signals of outputs E and F is compared 20 with the frequency division value of the output signal of a reference signal generator 21. This compared output outputs a control signal from the circuit 14. |
