[SI-LIST] Re: charge Pump Current in PFD
- From: "Guo Yawei" <ywguo527@xxxxxxxxxxx>
- To: parthsv@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Fri, 21 Nov 2003 20:46:53 +0800
Hello, Parthasarathy,
I hope my advice is a little helpful to your work.
First, you should determine the frequency range and the gain of VCO. Then
choose the loop bandwidth according to your application. Of course the
damping factor is also a key parameter you must choose according to the
application.
The phase noise of PLL results mainly from refence clock and VCO. If the
reference clock is a clean source, say a crystal oscillator, the loop
bandwidth can be made larger to surpress the phase noise of VCO. If the PLL
is used in a clock recovery circuit, the loop bandwidth must be made as
small as possible because the input signal is very noisy.
The choose of damping factor also depends on application. In applications
such as SONET, the damping factor is large. While for some applicatons
which requires frequency hopping, the damping factor must be chosen
carefully that the loop response settles in very short time.
The loop bandwidth, damping factor both related to the current in charge
pump. You can determine the current from classic formula in many textbooks.
Best regards,
Yawei Guo
>From: Parthasarathy Sampath <parthsv@xxxxxxxxx>
>Reply-To: parthsv@xxxxxxxxx
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] charge Pump Current in PFD
>Date: Thu, 20 Nov 2003 20:42:23 -0800 (PST)
>
>Hi All,
> What are the parameters that are needed to define
>the value of charge pump current in PFD? In other
>words, how do I know what is the right value of charge
>pump for a given PFD.
>
>Thanks in Advance,
>
>Regards,
>Partha!
>
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