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(三)相位控制电路录象机的相位控制电路一般都采用取样保持方式,它与速度控制不同。速度控制是对梯形波顶部全宽度取样,而相位控制都是在梯形波斜坡上取样。VHS 录象机的相位控制环路中,梯形波一般由基准信号形成,取样脉冲则由比较信号产生。相位控制环路方框图如图16(a)所示,比较信号与基准信号之间的相位变化,表现为取样脉冲在梯形波斜坡上的取样点发生变化,如图16(b)。以鼓伺服为例,如果磁鼓旋转相位正常,取样点在梯形波斜坡中点,输出为5V。如磁鼓相位滞后,则取样点上移,输出升高。如磁鼓相位超前,则取样点下移,输出下降。取样输出的相位误差电压对电机的相位进行调节,使之与基准保持一致。
(C) phase control circuit VCR phase control circuit are generally used sampling and holding, it is different from the speed control. The speed control is to sample the full width of the top of the trapezoidal wave and the phase control is to sample the trapezoidal wave ramp. VHS VCR phase control loop, the trapezoidal wave is generally formed by the reference signal, the sampling pulse is generated by the comparison signal. The block diagram of the phase control loop is shown in Figure 16 (a). The phase change between the signal and the reference signal is compared as shown in Figure 16 (b), which shows the sampling pulse changes at the sampling point on the trapezoidal wave ramp. Taking Drum Servo as an example, if the drum rotation phase is normal, the sampling point is at the midpoint of the trapezoidal wave ramp and the output is 5V. If the drum phase lag, then the sampling point up, the output increased. If the drum phase lead, then the sampling point down, the output drop. The phase error voltage of the sampled output regulates the phase of the motor to be consistent with the reference.