Phase Locked LOOP

The phase locked loop is most commonly used circuit in modern communication system. The concept of PLL was first developed in 1930. Since then it is used to generate, modulate, stabilized, demodulate and to recover a signal from noise in communication system. PLL is widely used in radio frequency synthesis.The phase noise and jitter effects the different building blocks of PLLs which causes instability to the system. The noise performance of the PLL outside the loop is totally depends on voltage controlled oscillator performance. The VCO is an Oscillator which contributes small random perturbation in the phase of the signal. In PLL, the bandwidth of the loop filter is an important factor in controlling the capture range as well as in reducing the noise.In PLL it is most challenging task to design a LF which remain stable and do not produce unwanted high frequency spurious oscillations.