| 摘要 |
PURPOSE:To prevent both the lowering of the C/N ratio of the phase synchronous loop caused by interference of the high-frequency signal source and the shift of the lock by adding the capacity between the earth and the inverter input terminal of the active low pass filter amplifier within the phase synchronous loop circuit. CONSTITUTION:The output of the phase comparator in the phase synchronous loop is applied to input terminal 40. And a low band pass filter is composed of resistance 41 and 42, capacitor 43 and N-channel MOS transistor Tr45. Then the output signal is transmitted through terminal C. Capacitor 46 is inserted between the earth and the gate input of MOSTr45 forming an inverter. As a result, the high-frequency component is attenuated at terminal C, and the lowering of the C/N ratio caused by the interference of other high-frequency signal sources can be prevented, furthermore preventing the lock shift of the phase synchronous loop. As capacity 46 is selected small enough compared with capacity 43, the characteristic change of the filter can be ignored substantially. |
