The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> generating 90 degree offset clock
https://designers-guide.org/forum/YaBB.pl?num=1155205688

Message started by vivkr on Aug 10^th, 2006, 3:28am

Title: generating 90 degree offset clock
Post by vivkr on Aug 10^th, 2006, 3:28am

Hi,

I would like to know if there is a quick and cheap way of generating a clock 90 degree offset in phase from a given clock. I do not have a 2x faster clock which I may use to do this. The jitter on the shifted clock is not important, and the input has a 50% duty cycle.

Regards
Vivek

Title: Re: generating 90 degree offset clock
Post by ACWWong on Aug 10^th, 2006, 4:10am

You can use a poly-phase splitter (RC network. If the input clock frequency has a wide frequnecy range you'll need 2 or 3 stages.)
see page 3 of the following
http://www.deas.harvard.edu/courses/es272/hw1_2005.pdf

i discussed this recently on this board....
http://www.designers-guide.org/Forum/YaBB.pl?num=1154528670

cheers

aw

Title: Re: generating 90 degree offset clock
Post by loose-electron on Aug 10^th, 2006, 11:10pm

A couple of flavors to solve this:

A ring oscillator with multiple delay elements gets you all kinds of phases with respect to the input. Probably the most common solve used here.

Another approach:

LPF until you got a sinusoid
Create a V to I converter
Dump the I into a series RC
Differentially observe the V across the resistor
Differentially observe the V across the capacitor

90 degrees of phase difference, Voila!
Mind you, that one requires some items to support the operating voltage on the capacitor from not wandering away. However, that approach was used in peak detectors in disk drive read channels for a number of years.

Jerry