Basic introduction of Phase Locked Loop (PLL)

Posted: 30/11/2010 in Generals

as i mentioned in my previous entry, i’m doing “design & simulation of PLL” for my FYP..perhaps people dont have a clue about what’s PLL right?
PLL is a -ve feedback control system that tries to generate an output signal whose off-set phase is same as the input ‘reference’ signal..widely use in telecommunication engineering field..
PLL may generate stable frequencies, generates clock signal, recover a signal from a noisy communication channel or distribute clock timing pulses.
A basic PLL constuction consist of 4 main blocks; Phase Frequency Detector(PFD), Charge Pump(CP), Low Pass Filter(LPF), & Voltage Controlled Oscillator(VCO).

BASIC PLL Block Diagram


1.  measures the difference in phase & frequency beetween reference & feedback signals

2. if there’s a difference, it generates ‘up’ or ‘down’ synchronized signal to the CP


3. if error signal from PFD is an ‘up’ signal, the CP pumps charge onto the LPF capacitor, which increases the Vcntrl

4. it it’s ‘down’ signal, the CP removes charge from the LPF capacitor, which decreases the Vcntrl


5. necessary to only allow DC signals into the VCO & also to store the charge from the CP


6. either to speed up @ down the feedback signal according to the error generated by the PFD

7. if PFD generates an ‘up’ signal, the VCO speed up

8. if ‘down’ signal, the VCO slow down. the output of the VCO is then fed back to the PFD in order to do the recalculate the phase & frequency difference

So thats only about the general operation of a PLL. For my title, I chose the “frequency synthesizer” & “clock generation” application for my PLL design.

Of course the detail of it definitely harder & tougher & like my examiner said to me during my FYP1 presentation, “u must try ur HARDEST if you want to complete this title” that’s spooky..

the lecturer got his point right because every block in the block diagram has its own complex circuitry, mainly its all about playing around with MOSFETs & i tell u it is not easy in each one of it (okay i lied, LPF’s easy. Consist just only 1 resistor & 2 capacitors)

Really hoping that god will give me such strength to complete this project.. bare in mind that i got another 4 elective subjects that also on going with their respective assignments/projects..  T_T


nota hamster : 3rd progress report due on week is week 1!!!!still got no progress at all T_T

nota kucing : aku telah melengkapkan rekod “the most entry in a month” ngn 10 entries..syabas!!produktiff!!

  1. ofrixy says:

    helped me a lot 🙂

  2. rahul says:

    i am also doing the same project i need some help plz……

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