| 摘要 |
PURPOSE:To form a highly accurate oscillation circuit without using any crystal resonator, and to change a frequency in a shot time by generating clocks by using the rotation detecting pulse signal of a polygon motor as a basic signal. CONSTITUTION:An encoder 205 with a slit is fixed to the scanner motor 203 of a rotary polygon mirror 202 and, when the motor is rotated, a photo- interruptor 204 detects the slit and outputs a pulse signal (FG) 207 which detects the rotational speed of the motor to a waveform shaping circuit 206. Then a TACH signal 101 outputted from the circuit 206 is converted and decided to an output voltage v1 by means of a frequency voltage conversion circuit 110 by using the frequency of the TACH signal and an error amplifier 107 decides the value of an output frequency (f) by controlling the input voltage V3 of a voltage-controlled oscillator (VCO) 105. The output signal (f) of the VCO 105 is inputted to a frequency divider 106 where the frequency of the signal (f) is divided and a clock signal F103 which is synchronous to a horizontal synchronizing signal (BD signal) 102 is obtained. Therefore, the frequency of the generated clock can be changed. |
