Rigol DG1022 square wave issues - Page 1
Forum section: electronics / beginners

author: ticktock3t
author_rank: Contributor
timestamp: December 02, 2012, 09:36:31 pm
content: I recently scored a Rigol DG1022 off ebay for $220. I like everything about it but when I was testing it out I noticed something very strange with its square wave output. At the lower end frequencies it outputs a nice square wave but when I crank it up to 5MHz the signal doesn't even look like a square wave anymore. It become highly distorted with a large overshoot. Should I just accept this or should I send this back to the seller.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 02, 2012, 09:39:34 pm
content: It could be the way you are measuring it

author: PA4TIM
author_rank: Super Contributor
timestamp: December 02, 2012, 09:42:13 pm
content: To see the true 5 MHz squarewave you must terminate the generator in 50 Ohm at the scope and use a scope that is at least 50MHz.So what scope you use and how you connect the generator to the scope.Also look in the manul from the Arigol what it's Tr and Tf is at 5 MHz.

author: ticktock3t
author_rank: Contributor
timestamp: December 02, 2012, 11:02:22 pm
content: Even at the lower frequencies I can still see, when I zoom into the square wave, an overshoot so could this be a problem with the function generator?

author: Unknown
author_rank: Unknown
timestamp: December 02, 2012, 11:31:28 pm
content: To repeat what Fred said: does terminating the function generator into 50 ohms help?

author: bernie
author_rank: Contributor
timestamp: December 03, 2012, 12:26:51 am
content: Here's the output from my DG1022, 50 Ohm terminated at both scope and function gen (utility menu), link directly with coax.The second is with scope and generator on High ZSeems passable, but is at it's 5MHz limitHope the screenshots help

author: kg4arn
author_rank: Unknown
timestamp: December 03, 2012, 12:46:47 am
content: It looks to me like there is less than 5% overshoot, which is within the spec on the datasheet.

author: ticktock3t
author_rank: Contributor
timestamp: December 03, 2012, 01:01:15 am
content: I somewhat get the same image that Bernie has posted, but as you can see the signal is not clean at all. Is that normal? Also, How come this distortion only applies to the square wave and not to the other waves. I have heard of square waves overshooting before. I'm going to upload some pictures from my oscilloscope soon.

author: Unknown
author_rank: Unknown
timestamp: December 03, 2012, 01:22:36 am
content: The manual lists the allowed aberrations in the square wave output. Rise / fall time is < 20 ns typical from 10% to 90%, so a typical DG1022 will take up to 20 ns to rise from 10% the output amplitude to 90%. Overshoot is < 5% typical, so on a rising edge a typical DG1022 will overshoot the high level by 5% of the amplitude. Note that none of these are guaranteed specs.Edges of square waves contain more high frequency content than for example sines with the same period, so imperfections in both function gen and cable are much more noticeable (hence the difference between high impedance and properly terminated scope input). For square waves the bandwidth depends on the rise time, not on the repetition rate. Sine waves (ideally) contain just one frequency, so an imperfect frequency response will only change the amplitude flatness. The human eye also sucks at visually detecting distortion in sine waves.

author: flolic
author_rank: Frequent Contributor
timestamp: December 03, 2012, 10:07:04 pm
content: Same setup as bernie's (high Z) on my DS1102E scope:

author: ticktock3t
author_rank: Contributor
timestamp: December 04, 2012, 02:54:52 am
content: Does anyone else find this much distortion strange? It doesn't even look like a square wave anymore.

author: robrenz
author_rank: Super Contributor
timestamp: December 04, 2012, 03:43:26 am
content: My DG1022 with inline 50 Ohm termination into rigol 1052EFirst is 5V PP at 5MSecond is 10V PP at 5M

author: w2aew
author_rank: Super Contributor
timestamp: December 04, 2012, 03:58:21 am
content: Quote from: ticktock3t on December 04, 2012, 02:54:52 amNot really. Depends entirely on the speed/bandwidth of the generator and the scope, as well as the quality of the coax cable and the termination. In this case, the generator spec states that the max square wave frequency is only 5 MHz. So, it is NOT going to look ideal anymore at the max rated output speed. Compared to other wave shapes, a square wave places the largest demand on the speed/BW on the output buffer. Bottom line, looks like I'd expect for a generator that's only rated for a 5 MHz square wave.http://www.rigolna.com/products/waveform-generators/dg1000/dg1022/