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PHASE LOCKED LOOP (PLL) BLOCK DIAGRAM



pll block diagram




Phase locked loop is a feedback loop consisting of a phase detector, a low pass filter, operational amplifier, and a voltage controlled oscillator. It plays the same role in the Frequency or phase world as the op amp does in voltage world. The op amp has two voltage inputs Inverting and NonInverting. Similarly the PLL has two inputs, the PLL's feedback input is normally connected to circuits output. Digital frequencies are normally applied. The op amp changes its output voltage to whatever values it is necessary to drive the difference in voltage between its two inputs to zero. The Phase locked loop changes its output Phase and Frequency to whatever Frequency or Phase is necessary to make the two input frequencies and Phase track. Placing a frequency divider in the feedback of a PLL causes the output frequency to be increased by the amount of feedback divider Similarly in op amp.

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