What is PLL control?
A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a variable frequency oscillator and a phase detector in a feedback loop.
What is the purpose of a PLL?
The main purpose of a PLL circuit is to synchronize an output oscillator signal with a reference signal. When the phase difference between the two signals is zero, the system is “locked.” A PLL is a closed-loop system with a control mechanism to reduce any phase error that may occur.
How is the stability of a PLL determined?
PLL design. Stability can be determined by examining the transfer function of the PLL in an open state. As seen, a condition of open loop gain of unity and a phase angle of -180 degrees must be avoided for stable opera- tion of the PLL. This can be accomplished by the proper selection of the loop filter parameters.
How is phase lock time determined in a PLL?
The loop bandwidth determines the frequency and phase lock time. Since the PLL is a negative feedback system, phase margin and stability issues must be considered. Spectral purity of the PLL output is specified by the phase noise and the level of the reference-related spurs.
Which is the transfer function of the PLL?
T(s) is the closed loop PLL transfer function in the frequency domain (Qrandbeing the input and output signal respectively), G(s) = KpF(s)Kds is the open loop transfer function (complex) of the PLL, Kp is the transfer function of the phase detec- tor in Volts1 Hz, Kds is the transfer function of the VCO in Hz/
Why do we need a PLL design program?
Because of the many tradeoffs involved, the use of a PLL design program such as the Analog Devices’ ADIsimPLL™ allows these tradeoffs to be evaluated and the various parameters adjusted to fit the required specifications. The program not only assists in the theoretical design, but also aids in parts selection and determines component values.