Re: [time-nuts] Zero-Crossing Detector Design?
On 07/22/2012 01:39 AM, Bob Camp wrote: HI The Collins paper that Bruce referred to is the standard work on limiters / jitter / bandwidth. It can't and doesn't address all the possible issues in a full blown design. The math for the basic approach is all there though. Indeed. It's a good and recommended read. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
Maybe, it is on my list for the university IEEE download for months. And this is the only reference? I have seen some similar issues in a few BPSK receiver papers. Not for time-nuting but for S/N. - Henry Magnus Danielson schrieb: On 07/22/2012 01:39 AM, Bob Camp wrote: HI The Collins paper that Bruce referred to is the standard work on limiters / jitter / bandwidth. It can't and doesn't address all the possible issues in a full blown design. The math for the basic approach is all there though. Indeed. It's a good and recommended read. -- ehydra.dyndns.info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
Hi There are papers on limiters in radio IF's going back at least into the 1930's. That's a long... list. Bob On Jul 22, 2012, at 3:36 PM, ehydra wrote: Maybe, it is on my list for the university IEEE download for months. And this is the only reference? I have seen some similar issues in a few BPSK receiver papers. Not for time-nuting but for S/N. - Henry Magnus Danielson schrieb: On 07/22/2012 01:39 AM, Bob Camp wrote: HI The Collins paper that Bruce referred to is the standard work on limiters / jitter / bandwidth. It can't and doesn't address all the possible issues in a full blown design. The math for the basic approach is all there though. Indeed. It's a good and recommended read. -- ehydra.dyndns.info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
Wow, I have not checked this list for some time. But there is a lot said about zero crossing detectors. Lots and lots of replies, so many that I have not looked at all of them. 1. Do not use CMOS inverters. Even though so much has been published on using these in linear mode by adding a feedback resistor, they can be a nightmare. The fast ones (74HC, 74AC, etc) have so much high frequency gain they are likely to take off into oscillation on their own. 2. The first thing you can do to get a good clean zero crossing is to reduce the noise. This means to pass it thru a narrow band pass filter such as a crystal filter. The narrower this filter is the closer to a pure sinewave it becomes and the less noise you have. 3. In research when we want a precise trigger we use what is called a constant fraction discriminator. This may not be needed if you have a very clean signal and its amplitude does not vary and you are wanting to trigger exactly at zero. But a constant fraction discriminator triggers on a point that is a constant fraction of the amplitude of the signal. They require a delay so that a fraction of the peak of the cycle can be compared with the rising edge of that cycle. This is mostly used with triggering on pulses of varying heights and when subnanosecond timing is required. My suggestion is to clean up your signal as much as possible and reduce noise bandwidth using a bandpass filter and then use a low noise amplifier for the front end of your zero-crossing detector. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
Hi The feedback inverter is indeed a problem with fast logic, just bias it to mid point off the supply instead. Narrow filters can be both a good and a bad thing at the same time. They clean up the signal, but the also have delay. If they are narrow enough they have lots of delay. That would be ok, except it drifts with temperature. It also changes with input frequency. You can do a delay correction stage to help with the frequency variation part, but the delay correction adds more delay that's also temperature dependent. No easy solutions …. Bob On Jul 22, 2012, at 4:32 PM, Bill Fuqua wrote: Wow, I have not checked this list for some time. But there is a lot said about zero crossing detectors. Lots and lots of replies, so many that I have not looked at all of them. 1. Do not use CMOS inverters. Even though so much has been published on using these in linear mode by adding a feedback resistor, they can be a nightmare. The fast ones (74HC, 74AC, etc) have so much high frequency gain they are likely to take off into oscillation on their own. 2. The first thing you can do to get a good clean zero crossing is to reduce the noise. This means to pass it thru a narrow band pass filter such as a crystal filter. The narrower this filter is the closer to a pure sinewave it becomes and the less noise you have. 3. In research when we want a precise trigger we use what is called a constant fraction discriminator. This may not be needed if you have a very clean signal and its amplitude does not vary and you are wanting to trigger exactly at zero. But a constant fraction discriminator triggers on a point that is a constant fraction of the amplitude of the signal. They require a delay so that a fraction of the peak of the cycle can be compared with the rising edge of that cycle. This is mostly used with triggering on pulses of varying heights and when subnanosecond timing is required. My suggestion is to clean up your signal as much as possible and reduce noise bandwidth using a bandpass filter and then use a low noise amplifier for the front end of your zero-crossing detector. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
Narrow filters have high tempco on their group delay, so that's no good either. Didier KO4BB Bill Fuqua wlfuq...@uky.edu wrote: Wow, I have not checked this list for some time. But there is a lot said about zero crossing detectors. Lots and lots of replies, so many that I have not looked at all of them. 1. Do not use CMOS inverters. Even though so much has been published on using these in linear mode by adding a feedback resistor, they can be a nightmare. The fast ones (74HC, 74AC, etc) have so much high frequency gain they are likely to take off into oscillation on their own. 2. The first thing you can do to get a good clean zero crossing is to reduce the noise. This means to pass it thru a narrow band pass filter such as a crystal filter. The narrower this filter is the closer to a pure sinewave it becomes and the less noise you have. 3. In research when we want a precise trigger we use what is called a constant fraction discriminator. This may not be needed if you have a very clean signal and its amplitude does not vary and you are wanting to trigger exactly at zero. But a constant fraction discriminator triggers on a point that is a constant fraction of the amplitude of the signal. They require a delay so that a fraction of the peak of the cycle can be compared with the rising edge of that cycle. This is mostly used with triggering on pulses of varying heights and when subnanosecond timing is required. My suggestion is to clean up your signal as much as possible and reduce noise bandwidth using a bandpass filter and then use a low noise amplifier for the front end of your zero-crossing detector. 73 Bill wa4lav ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Sent from my Motorola Droid Razr phone with K-9 Mail. Please excuse my brevity. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Zero-Crossing Detector Design?
On 7/22/2012 2:41 PM, Bob Camp wrote: Hi The feedback inverter is indeed a problem with fast logic, just bias it to mid point off the supply instead. 1. Do not use CMOS inverters. Even though so much has been published on using these in linear mode by adding a feedback resistor, they can be a nightmare. The fast ones (74HC, 74AC, etc) have so much high frequency gain they are likely to take off into oscillation on their own. YMMV, but in the 5071A cesium standard I designed in a 74AC00 biased at half the supply voltage to make an 80 MHz clock from a sine wave. We never observed oscillations. The feedback resistor method may be optimum for getting the gate at the exact center of its range which might encourage oscillation. We did not have a requirement that the gate is stable with no input, like it might need to be if it were a front panel input on an instrument. Rick ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
