Explanation of TYPEs in PLL

[mady79]

Queries on PLL

Hi All,

I am trying to figure out what does TYPE in a PLL meant ??.I know it will tell ,how many poles are located at origin .Can some one relate the TYPE ,Order of the PLL in terms of Lock time & Frequency and phase drift changes in Reference Clock input frequency .

Thank you in advance !

 

[Teddy]

Re: Queries on PLL

Type I PLL loop filters show no integrating behaviour (non-integrating or averaging loop filter). They have no pole at the origin, their transimpedance is resistive at low frequencies. This means, the DC component of the output voltage is only determined by the duty cycle and the pulse amplitude of the input signal. The PD output has to pulse all the time to provide the tuning voltage for the VCO.

Type II PLL loop filters include an integrator creating a pole at the origin (integrating loop filter). Therefore, the transimpedance at low frequencies is capacitive. The output voltage depends on the history of the input signal - in locked state, only the non-idealities of PD / CP create pulses and a ripple on the VCO control voltage. The phase detector usually has a tri-state output.


Order is number of poles.

 

[colombo2]

Re: Queries on PLL

PLL type is the number of integrators in the loop transmission... The VCO acts as one integrator (voltage to phase).... So the lowest value for the Type is 1 because there is no PLL without a VCO.
A charge pump is a second integrator (I/SC) so a charge pump PLL is type-II

 

[mady79]

Re: Queries on PLL

I would like to know how to TYPE 2 PLL is able to track the changes in input reference frequency .