Fast marker pulse generator - Page 1
Forum section: electronics / projects

author: chilternview
author_rank: Frequent Contributor
timestamp: January 23, 2025, 11:35:29 am
content: I've been thinking of building a fast marker pulse generator for scope checking. The goal would be a max frequency of 500MHz (or even 1GHz). Using a 1GHz clock e.g. from an ADF4360-7, then fed into a divider chain to get 1-2-5 sequence out. The question is how to get divide by 2, 5 and 10 starting from 1GHz. I did notice the HMC394 which can do divide by N, where N is from 2 to 32. Nice, but very expensive (£34 in the UK). Is there a better (and cheaper) way?

author: tggzzz
author_rank: Super Contributor
timestamp: January 23, 2025, 03:49:27 pm
content: Ǹeed to specify the precision required, and the use case.Analogue scopes' sweep time is typically specified to be 2%, and not necessarily linear.Digital scopes' sweep speed is derived from a crystal, so will be much more accurate and linearity shouldn't be an issue.Consider using an RF generator, optionally driven from an external calibrated and adjusted 10MHz source.

author: jonpaul
author_rank: Super Contributor
timestamp: January 23, 2025, 04:31:07 pm
content: we use Tek TM501 and similar time/marker gens, and Leo Bodnar 40 pS fast pulser.No need for GHz markers, as 99% of scope sweeps just ahve ONE or a few CAL adjust.The ratios oaver 10 nS/div ae usually 2-5% accurate andmany digitally derived.Th fast edge pulsers run at 1 or 10 MHz and the edges abbesration and rise is controlled.As rings may extend for many nS or even uS a slower PRF is better for transient CALj

author: chilternview
author_rank: Frequent Contributor
timestamp: January 23, 2025, 04:49:42 pm
content: Quote from: tggzzz on January 23, 2025, 03:49:27 pmThe intent was for (analog) scope calibration, so accuracy not extreme, but there are a few times recently that a simple pulse generator with reasonably fast edges (1nS?) would have been useful. An RF generator is quite a good idea but would need a squarer on the output. A TG501 would do but they are hard to find these days.

author: tggzzz
author_rank: Super Contributor
timestamp: January 23, 2025, 05:35:43 pm
content: Quote from: chilternview on January 23, 2025, 04:49:42 pmFollow the analogue scopes' service instructions to see what repetition period you require. 1GHz would only be useful if measuring the sweep linearity of a multi-GHz scope, and there aren't many of those!For adjusting the vertical response, a 1GHz signal wouldnotwork, but having a risetime <1ns (not nanoSiemen) is preferable. Again, RTFServiceM to see what risetime your scope requires.Using (and making) a <1ns risetime generator isn't difficult, but it requires care and understanding the fundamental physics of electronic components.

author: David Hess
author_rank: Super Contributor
timestamp: January 23, 2025, 06:03:36 pm
content: Older time-mark generators use frequency multiplication and injection locking to generate higher frequencies from a low frequency reference.Injection locking can also be used for division. The output of the 200 and 500 MHz markers is a sine wave anyway.I suspect your time is better spent refurbishing an old time-mark generator.Quote from: tggzzz on January 23, 2025, 05:35:43 pmThe higher frequencies from a time-mark generator are used to calibrate the scale and linearity of the x10 horizontal modes at the fastest sweep speeds, where even a lower bandwidth oscilloscope can operate with an effective sweep speed below 10 nanoseconds per division. My 500 MHz 7904 supports sweep speeds down to 500 picoseconds per division in this way, but even my 100 MHz oscilloscopes operate down to 2 or 5 nanoseconds per division.

author: chilternview
author_rank: Frequent Contributor
timestamp: January 23, 2025, 06:10:46 pm
content: Quote from: David Hess on January 23, 2025, 06:03:36 pmI suspect you're probably right!