What are the 3 main blocks of PLL?
The block diagram of a basic PLL is shown in the figure below. It is basically a flip flop consisting of a phase detector, a low pass filter (LPF),and a Voltage Controlled Oscillator (VCO).
What is the concept behind PLL?
A phase-locked loop (PLL) is an electronic circuit with a voltage or voltage-driven oscillator that constantly adjusts to match the frequency of an input signal. PLLs are used to generate, stabilize, modulate, demodulate, filter or recover a signal from a “noisy” communications channel where data has been interrupted.
What is the purpose of loop filter in PLL?
Loop filter: This filter is used to filter the output from the phase comparator in the phase locked loop, PLL. It is used to remove any components of the signals of which the phase is being compared from the VCO line, i.e. the reference and VCO input.
What is free running in PLL?
This PLL free running frequency is determined by its internal frequency determining components. As explained in fig. 1 when frequency changes, phase detector and LPF will produce new DC voltage. This voltage force VCO frequency to change and adopt to the new input frequency.
What is an example of PLL?
Automobile race analogy. As an analogy of a PLL, consider a race between two cars. One represents the input frequency, the other the PLL’s output voltage-controlled oscillator (VCO) frequency. Each lap corresponds to a complete cycle.
What is free running frequency of PLL?
Without connecting any input signal, apply power and use an oscilloscope or frequency counter to measure the free- running frequency at VCO out. It should be close to f0 = 1.2/4RTCT ≈ 1360 Hz. Set your function generator to output a sine wave at the measured value of f0.
Why charge pump is used in PLL?
Charge pump make use of switching devices for controlling the connection of voltage to the capacitor. Charge pump is one of the important parts of PLL which converts the phase or frequency difference information into a voltage, used to tune the VCO.
What is phase margin in PLL?
In electronic amplifiers, the phase margin (PM) is the difference between the phase lag φ (< 0) and -180°, for an amplifier’s output signal (relative to its input) at zero dB gain – i.e. unity gain, or that the output signal has the same amplitude as the input.
Why is VCO used?
VCOs are used in function generators, phase-locked loops including frequency synthesizers used in communication equipment and the production of electronic music, to generate variable tones in synthesizers.
What is the difference between PLL and 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.