| 摘要 |
PURPOSE:To hold an output frequency to a value before a fault takes place even if a reference input signal is faulty by providing a logic circuit blocking a clock signal to a counter circuit in response to an output signal of a fault detection circuit. CONSTITUTION:If a fault takes place in the reference input signal given to an input terminal 100, a fault detection circuit 7 detects the fault immediately and produces a logic level 0. As a result, a clock signal from a clock generating circuit 6 is blocked by a logic circuit 8 and not given to a counter circuit 3. Thus, an output signal of the counter circuit 3 keeps the value before a fault takes place in the reference input signal. Thus, the output voltage of the D/A converter circuit 4 converting the signal into an analog voltage, that is, the control voltage of the voltage-controlled oscillator 5 keeps the value before a fault takes place in the reference input signal, then the output frequency of the voltage controlled oscillator 5 remains unchanged, that is, a value before the fault takes place in the reference input signal. |
