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Design >> Analog Design >> A charge pump circuit
https://designers-guide.org/forum/YaBB.pl?num=1352904325

Message started by Yutao Liu on Nov 14^th, 2012, 6:45am

Title: A charge pump circuit
Post by Yutao Liu on Nov 14^th, 2012, 6:45am

Hello everyone,
I found a charge pump topology as shown below.
The control voltage of VCO is provided by the right-hand-side branch, instead of the left-hand-side. Have you seen this circuitry before? What is it called? I want to do some research on this.
Furthermore, I think the capacitor C1 still affects the bandwidth of the PLL, even though it is not in the loop directly. Is that right?

Thanks,
Yutao Liu

Title: Re: A charge pump circuit
Post by raja.cedt on Nov 14^th, 2012, 7:13am

hello,
this ckt is wrong. Please find the attached ckt. C1 Has nothing to do with BW, it is just to solve charge injection problem, in principle it is not required.
Thanks,
Raj.

Title: Re: A charge pump circuit
Post by Yutao Liu on Nov 14^th, 2012, 7:25am

Hello Raj,
Thanks for your quick reply.
The ckt in your reply is a classical current steering charge pump.
But why do you think my ckt is wrong?
In my opinion, the current charging to/discharging from (right branch) the loop filter can represent the phase error all the same.

Thanks,
Yutao Liu

Title: Re: A charge pump circuit
Post by raja.cedt on Nov 14^th, 2012, 7:45am

hello,
Yes in principle your concept doesn't work.
If Up switch turns on C1 connected across bottom current source and at node x no current will flow into loop filter. So no change in the Vctl.

Thanks,
Raj.

Title: Re: A charge pump circuit
Post by loose-electron on Nov 14^th, 2012, 4:02pm

the circuit Raj shows is much more common and probably will work better.

Title: Re: A charge pump circuit
Post by Lex on Nov 15^th, 2012, 1:55am

loose-electron wrote on Nov 14^th, 2012, 4:02pm:

the circuit Raj shows is much more common and probably will work better.

I agree, but isn't it patented?

Title: Re: A charge pump circuit
Post by raja.cedt on Nov 15^th, 2012, 2:51am

Hello lex,
i guess it is not a patent, in 99% of products you see this circuit. I personally designed around 3 commercial circuits with the same charge pump some minor modification for matching.

Thanks,
raj,

Title: Re: A charge pump circuit
Post by Yutao Liu on Nov 15^th, 2012, 6:14am

Hello raj,
I forgot putting a bias circuit on the ckt. Sorry for my carelessness. The ckt is renew as the attachment. Please check it.

Thanks,
Yutao Liu

Title: Re: A charge pump circuit
Post by raja.cedt on Nov 15^th, 2012, 6:21am

Dear Yutao Liu ,
Problem is not on that side, in fact without bias it would have been better, but problem is other side(loop filter side)

Thanks,
Raj.

Title: Re: A charge pump circuit
Post by Lex on Nov 15^th, 2012, 7:30am

raja.cedt wrote on Nov 15^th, 2012, 2:51am:

Raj,
It looks like the circuit described in: http://www.google.com/patents/US5825640 (figure 7 on page 4 of the PDF)

Title: Re: A charge pump circuit
Post by loose-electron on Nov 15^th, 2012, 8:31pm

that's my definition of a patent that will never stand up in court.

the charge pump in the patent was in wide use 10 years or more prior to the patent.

Title: Re: A charge pump circuit
Post by Lex on Nov 16^th, 2012, 1:52am

Hey Jerry,

To be honest I've seen this circuit a few times as well, but I wondered why a company such as Patexia would offer $ 5000 for prior art? Any clue?