Hi Magnus, So I guess the verdict is that it is best to band limit your clock signal with a low-pass filter. This filter is then still supposed to still allow the necessary rise time for adequate PSSR. Doesn't PCB track impedance do this type of band limiting for you? Or do you suggest adding a separate RC-stage of some kind? The reflections due to impedance mismatch still steers me away from this option.
Regards, Stephan Sandenbergh Message: 6 Date: Wed, 28 Jun 2006 14:59:41 +0200 (CEST) From: Magnus Danielson <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Conditioning clock signal paths To: [email protected], [EMAIL PROTECTED] Message-ID: <[EMAIL PROTECTED]> Content-Type: Text/Plain; charset=us-ascii From: "Poul-Henning Kamp" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Conditioning clock signal paths Date: Wed, 28 Jun 2006 12:37:29 +0000 Message-ID: <[EMAIL PROTECTED]> > In message <[EMAIL PROTECTED]>, "Stephan Sandenbergh" writ > es: > > >Now for the paradox: Do you filter your digital signal to lower the noise > >bandwidth? Or do you want a high as possible rise time (slew rate) to get > >the best PSSR? > > The advantage to digital signals (ie: square-oid signals) as opposed > to analog signals (ie: sines) is that the slew-rate is higher. That > means that it is less important at which precise voltage the > L->H or H->L transistion happens and therefore you don't need > precise analog reference voltages in your logic circuits. > > The low slewrate of a sine would mean that even small changes > in threshold voltage would come out as large jitters in time. Worse yet, the broadband noise will make sure to add jitter. There is a very direct relationship between slew-rate, noise and jitter. This jitter will limit the time-resolution of the measurement. Slew-rate is in a very direct relation to amplitude and frequency. Slow changes in offset (due to power and temperature) will certainly contribute to wander effects. Cheers, Magnus ------------------------------ _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts End of time-nuts Digest, Vol 23, Issue 26 ***************************************** _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
