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What would happen if the input frequency of PLL is not within the capture range?
The PLL can track and “lock” to any input frequency in this range. If an input signal out of the lock range is applied, the PLL will not synchronize. If the input signal is initially outside of the lock range, the PLL will not lock.
What is the basic principle of PLL?
The input signal is directly proportional to the output frequency of the VCO (fo). The input and output frequencies are compared and adjusted through the feedback loop until the output frequency is equal to the input frequency. Hence, the PLL works like free running, capture, and phase lock.
What does VCO stand for?
A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input.
How does the PLL circuit affect the VCO?
A VCO contains an adjustable tuning element, such as a varactor diode with a capacitance that changes depending on the input voltage. The PLL circuit is thus a kind of feedback control system for the VCO. The required input or control voltage to the VCO is often higher than the supply voltage available to the PLL circuit.
What is the phase noise of a PLL oscillator?
The phase noise performance of the voltage controlled oscillator is the dominant factor of phase noise outside the PLL loop bandwidth. Although close in noise is reduced by the action of the PLL, outside the loop bandwidth there is no reduction of VCO phase noise.
How does voltage controlled oscillator affect loop design?
The voltage controlled oscillator gain affects some of the overall loop design considerations and calculations. The VCO response curves can be seen to be relatively straight at lower frequencies.
What is a phase locked loop ( PLL ) circuit?
A phase-locked loop (PLL) circuit is a feedback system that combines a voltage controlled oscillator (VCO) and a phase detector in such a way that the oscillator signal tracks an applied frequency or phase modulated signal with the correct frequency and phase.