| 摘要 |
PURPOSE:To improve the pull in time at out of synchronism by inserting an amplifier with exponential characteristic between an output of a phase detector and a control input of a voltage controlled oscillator so as to improve the frequency stability at the steady-state. CONSTITUTION:A log amplifier 5 gives an exponential characteristic to an output of a phase detector 3 and gives the result to a voltage controlled oscillator 1. Thus, the oscillated frequency of the voltage controlled oscillator 1 changes exponentially to a phase detection output. Thus, even if the time constant of a low pass filter rectifying the output of the phase detector 3 is decreased, since the change in the oscillation frequency with respect to the change in the control voltage at the steady-state is less, the instable oscillated frequency is prevented. On the other hand, in case of out of synchronization, the change in the oscillation frequency is large and a sufficiently large control voltage is produced, the tracking speed, that is, the pull in time characteristic is improved. |
