[SI-LIST] Re: PLL Natural Freq
- From: steve weir <weirsp@xxxxxxxxxx>
- To: parthsv@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Sat, 01 May 2004 12:49:59 -0700
Parthal, it is the natural frequency of the typical second-order transfer
function of the closed loop. Phase comparator gain is in volts / radians,
while VCO gain is in radians / second / volt. Given only DC gain, the
system is first order and unconditionally stable yielding
V/S/V. Unfortunately, it is not particularly useful as something has to be
done to establish the DC operating point. In most implementations an
integrator serves this purpose, adding a second order to the transfer function.
The system will oscillate if it fails stability criteria. If the damping
is less than unity, which is typical, the system rings in response to an
impulse or step. All of this can be found in Gardner, Best, or the many
application notes that are out there.
Steve.
At 04:03 AM 5/1/2004 -0700, Parthasarathy Sampath wrote:
>Hi All,
> Intutively, what does natural freq of a PLL
>represent?
> Since it means freq of oscillation of the whole
>system, does it represent, the unity gain of frequency
>of the closed loop system?
> In that case, will the system oscillate provided the
>value of loop gain > 1?
> Since the system is designed to be stable(from the
>design eqns), does it mean, system will never
>oscillate at Wn??
>
>
>Thanks in Advance,
>
>Regards,
>Partha!
>
>
>
>
>
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