Designer’s Guide Community

RobG Community Fellow Offline Posts: 570 Bozeman, MT	Re: question about charge pump in PLL Reply #15 - Dec 06^th, 2011, 6:50am loose-electron wrote on Dec 6^th, 2011, 2:15am: ece.wpi.edu/analog/resources/PLLTutorialISSCC2004.pdf see page 50 of the above I like it 8-)
Back to top	IP Logged

loose-electron

Senior Fellow

Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California

Re: question about charge pump in PLL
Reply #16 - Dec 6^th, 2011, 10:12am

I refine that structure a bit with:

Minimum size transitors in the H bridge to minimize charge injection.

PMOS transistors top of bridge only.

NMOS transistors bottom of bridge only

limit signal amplitude ti the 4 currrent steering switches

All of the above gets the device closer to ideal switches to redirect the charge pump current and reduce transient signal current injection.

Back to top

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

IP Logged

lunren

Community Member

Offline

Posts: 82
Asia

Re: question about charge pump in PLL
Reply #17 - Dec 13^th, 2011, 10:50pm

loose-electron wrote on Dec 6^th, 2011, 10:12am:

I refine that structure a bit with:

Minimum size transitors in the H bridge to minimize charge injection.

PMOS transistors top of bridge only.

NMOS transistors bottom of bridge only

limit signal amplitude ti the 4 currrent steering switches

All of the above gets the device closer to ideal switches to redirect the charge pump current and reduce transient signal current injection.

Hi Jerry,
Why you didn't use CMOS switches? I think based on the modifications you did (small size and limited signal swing to control switches), if you use CMOS instead only PMOS on top and only NMOS on bottom, it might be better to reduce charge sharing and clock feedthrough?

By the way, with your modification, how much reference spur can you get with this charge pump?

Thanks,

Lunren

Back to top

Best Regards,

Lunren

IP Logged

RobG

Community Fellow

Offline

Posts: 570
Bozeman, MT

Re: question about charge pump in PLL
Reply #18 - Dec 16^th, 2011, 11:18am

lunren wrote on Dec 13^th, 2011, 10:50pm:

loose-electron wrote on Dec 6^th, 2011, 10:12am:

I refine that structure a bit with:

Minimum size transitors in the H bridge to minimize charge injection.

PMOS transistors top of bridge only.

NMOS transistors bottom of bridge only

limit signal amplitude ti the 4 currrent steering switches

All of the above gets the device closer to ideal switches to redirect the charge pump current and reduce transient signal current injection.

Hi Jerry,
Why you didn't use CMOS switches? I think based on the modifications you did (small size and limited signal swing to control switches), if you use CMOS instead only PMOS on top and only NMOS on bottom, it might be better to reduce charge sharing and clock feedthrough?

By the way, with your modification, how much reference spur can you get with this charge pump?

Thanks,

Lunren

Lunren, I think Jerry is talking about using diff-pairs to steer current instead of switches. With a diff pair you only need a few hundred millivolts to steer the current between the opamp output and the capacitor network.

rg

Back to top

IP Logged

loose-electron

Senior Fellow

Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California

Re: question about charge pump in PLL
Reply #19 - Dec 18^th, 2011, 2:13pm

At the end of the day it looks more like current
steering than rail to rail gate driven switches.

Spurs? Depends on your primary hold
capacitors and similar issues. Specific numbers are unique
to a system.

Key thing here is getting the current steering
switches to look as close to ideal as possible.

Also, things like the PFD need to account for
the zero phase point and avoiding deadbanding issues.

PLL's have a lot of little things that affect performance.
I could write a book!

Back to top

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

IP Logged

lunren Community Member Offline Posts: 82 Asia	Re: question about charge pump in PLL Reply #20 - Dec 18^th, 2011, 11:30pm Hi Rg, I got it. Thanks.
Back to top	Best Regards, Lunren IP Logged

lunren

Community Member

Offline

Posts: 82
Asia

Re: question about charge pump in PLL
Reply #21 - Dec 18^th, 2011, 11:53pm

loose-electron wrote on Dec 18^th, 2011, 2:13pm:

At the end of the day it looks more like current
steering than rail to rail gate driven switches.

Spurs? Depends on your primary hold
capacitors and similar issues. Specific numbers are unique
to a system.

Key thing here is getting the current steering
switches to look as close to ideal as possible.

Also, things like the PFD need to account for
the zero phase point and avoiding deadbanding issues.

PLL's have a lot of little things that affect performance.
I could write a book!

Hi Jerry,
What do you mean by zero phase point? I think you are saying the phase difference between reference clock and feedback clock should be zero, right? But I think this phase error is more related to mismatching in charge pump other than PFD itself (assuming the up and down path in PFD is perfectly matching).

Back to top

Best Regards,

Lunren

IP Logged

loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: question about charge pump in PLL Reply #22 - Dec 19^th, 2011, 12:18pm Zero phase point is when the two inputs to the PFD are exactly in line with each other. Behavior needs to be carefully examined here. PFD at this point is often created to give equal size up-down pulses Static phase errors are what you mention, offsets, mismatches, etc.
Back to top	Jerry Twomey www.effectiveelectrons.com Read My Electronic Design Column Here Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical IP Logged

aaron_do Senior Fellow Offline Posts: 1398	Re: question about charge pump in PLL Reply #23 - Dec 19^th, 2011, 5:40pm Quote: PLL's have a lot of little things that affect performance. I could write a book! Looking forward to it :D
Back to top	there is no energy in matter other than that received from the environment - Nikola Tesla IP Logged

Lex Senior Member Offline Posts: 201 Eindhoven, Holland	Re: question about charge pump in PLL Reply #24 - Dec 19^th, 2011, 11:39pm loose-electron wrote on Dec 18^th, 2011, 2:13pm: ... I could write a book! Do you already accept pre-orders? �;D
Back to top	IP Logged

loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: question about charge pump in PLL Reply #25 - Dec 21^st, 2011, 10:43am Thing is electronics books don't sell to a wide audience. It's on my bucket list.... Serious interest?
Back to top	Jerry Twomey www.effectiveelectrons.com Read My Electronic Design Column Here Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical IP Logged

Forum Administrator YaBB Administrator Offline Posts: 145	Re: question about charge pump in PLL Reply #26 - Dec 21^st, 2011, 11:48am Jerry, Writing a book is a big endeavor, and if it does not become a widely used textbook is generally not that profitable. As an alternative, you might consider writing smaller tutorials. I would be happy to publish them on this site. You would not make any money of course, but you can have a big impact. -Ken
Back to top	IP Logged

aaron_do

Senior Fellow

Offline

Posts: 1398

Re: question about charge pump in PLL
Reply #27 - Dec 21^st, 2011, 4:30pm

Throughout my postgrad studies - and even now - I've been looking for that book that will explain things in a more engineering fashion. i.e the practical implementation of all the fundamentals we see in textbooks and papers. I think it would be a good read and a useful reference...I'm always looking for good tutorial papers too though.

Aaron

Back to top

there is no energy in matter other than that received from the environment - Nikola Tesla

IP Logged

loose-electron

Senior Fellow

Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California

Re: question about charge pump in PLL
Reply #28 - Dec 22^nd, 2011, 4:14am

Forum Administrator wrote on Dec 21^st, 2011, 11:48am:

Jerry,
� � Writing a book is a big endeavor, and if it does not become a widely used textbook is generally not that profitable. As an alternative, you might consider writing smaller tutorials. I would be happy to publish them on this site. You would not make any money of course, but you can have a big impact.

-Ken

Ken:
Yeah, I am very aware that its a thankless and profitless endeavor.
McGraw Hill wanted me to do something for them a while back and I deferred
due to lack of time and sufficient financial motivation.
Let me give some thought to your suggestion.

Jerry

Back to top

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

IP Logged

loose-electron

Senior Fellow

Offline

Best Design Tool =
Capable Designers

Posts: 1638
San Diego California

Re: question about charge pump in PLL
Reply #29 - Dec 22^nd, 2011, 4:20am

aaron_do wrote on Dec 21^st, 2011, 4:30pm:

Throughout my postgrad studies - and even now - I've been looking for that book that will explain things in a more engineering fashion. i.e the practical implementation of all the fundamentals we see in textbooks and papers. I think it would be a good read and a useful reference...I'm always looking for good tutorial papers too though.

Aaron

Well, as a reviewer for 6-8 years for both IEEE JSSC and IEEE MTT,
I was always pushing for the inclusion of the practical and useful aspects
in addition to the mathmatical analysis.

Never happened, you review a paper with a panel of others and it
gets shot down. Most reviewers are coming at it from the view
of a university professor.

Thats the big reason I write for the trade magazines instead.

Back to top

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

IP Logged