Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Phase locked loops and confusion.
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Sun, 24 Nov 2002 07:37:44 -0000
NNTP-Posting-Date: Sun, 24 Nov 2002 07:37:46 GMT
John Larkin wrote:
> On Sat, 23 Nov 2002 07:41:37 -0000, "Kevin Aylward"
>> This don't make sense to me. I don't see any reason for the charge
>> pump to have a dead band. A charge pump is nothing more then a
>> switched source and sink of current. The dead band is usually in the
>> phase detector, that is, if steps are not taking to correct it.
> the 4046-type charge-pump circuit (widely copied) has the problem
> that, near balance, the pullup and pulldown current squirters are
> being asked to operate smoothly down to zero pulse width, which they
> can't. An HC4046, using the charge-pump detector, can add several ns
> of loop jitter because of this deadband. Interestingly, if you add a
> resistor from pin 13 to ground, this will force the pd off center
> (force a finite pulse width on the pullup side) and reduce jitter
I agree, I did address in in another post. I was not clear on what you
were claiming at first.
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