rigol-DS1054Z--Vertical distortion problem - Page 1
Forum section: electronics / testgear

author: biank88
author_rank: Contributor
timestamp: January 18, 2017, 11:40:57 am
content: Hi there folks, its a pleasure to join this community!I've just received my new Rigol 1054Z oscilloscope and I've noticed something that I've never considered before.In particular, If I hook up CH1 (1X, 1V/div) to the test signal (3Vpp, 1Khz) I get the following trace:Now, if I change the vertical resolution to 200mv/div I get heavly distorted signals like:Can this be considered "normal" behaviour for the frontend amplifiers?Thanks for your attention!

author: nctnico
author_rank: Super Contributor
timestamp: January 18, 2017, 11:43:31 am
content: This is normal and every oscilloscope has this 'problem'. The phenomenon is called amplifier overdrive recovery. Once a transistor is saturated (overdriven) it takes a while to exit this state.

author: borjam
author_rank: Unknown
timestamp: January 18, 2017, 11:48:35 am
content: Yes, it's normal. When using a digital oscilloscope it's tempting to think that one can use the vertical controls to "zoom in" into a signal. Alas, it is possible only to a certain limited extent. You are not "zooming" but actually amplifying and adding some DC offset to the input signal fed to the A/D converter, which can indeed add distortion.Anyone who hasn't made this mistake at least once, raise your hand! (I keep mine lowered)

author: biank88
author_rank: Contributor
timestamp: January 18, 2017, 11:51:33 am
content: Thanks for the quick reply.I've studied the overdrive recovery for opamps but I've never seen any scope review giving any details about this effect.

author: borjam
author_rank: Unknown
timestamp: January 18, 2017, 12:02:02 pm
content: Quote from: biank88 on January 18, 2017, 11:51:33 amA link to this document was posted on another similar thread some time ago.http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf

author: tautech
author_rank: Super Contributor
timestamp: January 18, 2017, 08:37:39 pm
content: 2 threads that discuss thisapparentdistortion in more depth:https://www.eevblog.com/forum/testgear/ds1054z-distortion-issue/https://www.eevblog.com/forum/testgear/rigol-ds1054z-offset-range-limits/Read ^^^ and understand.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 19, 2017, 03:09:42 am
content: Hmmm.... I could swear that I've already seen those screenshots somewhere...

author: 2N3055
author_rank: Super Contributor
timestamp: January 19, 2017, 10:03:02 am
content: Rigol DS 1000Z series:Offset Range (Probe ratio is 1X)1 mV/div to 499 mV/div: ±2 V500 mV/div to 10 V/div: ±100 V

author: JPortici
author_rank: Super Contributor
timestamp: January 19, 2017, 10:41:30 am
content: is that guy spamming those screenshots or what?

author: Fungus
author_rank: Super Contributor
timestamp: January 19, 2017, 12:36:13 pm
content: Looks like everybody's posting in two threads.

author: nctnico
author_rank: Super Contributor
timestamp: January 19, 2017, 12:48:58 pm
content: Quote from: JPortici on January 19, 2017, 10:41:30 amHe probably is but it does make me wonder whether Micsig has really solved overdrive issues or that the poster cherry picked a range where the analog frontend has the largest dynamic range. Still it is pretty impressive and usefull.

author: rstofer
author_rank: Super Contributor
timestamp: January 19, 2017, 06:15:12 pm
content: But why use an x1 probe setting? Not that it has anything to do with the original traces but still...

author: nctnico
author_rank: Super Contributor
timestamp: January 19, 2017, 06:30:09 pm
content: The signal is probably fed into the oscilloscope with a coax cable from a function generator but that doesn't really matter for what is shown on screen.

author: hgjdwx
author_rank: Regular Contributor
timestamp: January 20, 2017, 02:55:51 am
content: Don't doubt my tests! I just want everyone to know the truth, am I wrong? Mikeselectricstuff can prove that he can do the same test. Sorry, my English is not good.Using the ground spring (the native 2V self-tuning signal)

author: Fungus
author_rank: Super Contributor
timestamp: January 20, 2017, 09:37:57 am
content: Quote from: hgjdwx on January 20, 2017, 02:55:51 amWhat happens if you set the probe input to x10 mode (the usual setting)?

author: hgjdwx
author_rank: Regular Contributor
timestamp: January 20, 2017, 10:23:13 am
content: Quote from: Fungus on January 20, 2017, 09:37:57 amI set the probe input and scope to x10 mode, Test the native 2V self-tuning signalUsing ground clampUsing the ground spring

author: hgjdwx
author_rank: Regular Contributor
timestamp: January 21, 2017, 02:56:20 am
content: This is of practical value,When calibration probe compensation,This is just a simple example, you should be good at discovering

author: David Hess
author_rank: Super Contributor
timestamp: January 22, 2017, 06:24:56 pm
content: Quote from: nctnico on January 18, 2017, 11:43:31 amNot every oscilloscope suffers from overdrive induced distortion; sampling oscilloscopes are immune to non-destructive overdrive making them useful even at low bandwidths where a normal oscilloscope would usually be preferred. (1) Some old analog and digital storage oscilloscopes include cascode circuits for wider operating range and/or clamp circuits which limit the effects of overdrive.The cause it not always transistor saturation. Low leakage diodes used as clamps usually have slow reverse recovery time. Amplifier stages which rely on balanced operation can suffer from thermal imbalance.(1) This might explain why some Tektronix sampling instruments support real time operation with both sampling and real time timebases.Quote from: borjam on January 18, 2017, 11:48:35 amAnalog oscilloscopes almost always suffer from the same problem.Jim Williams discussed the problem in detail and shows examples of how subtle the problem can be and how to detect it in appendix B ofLinear Technology application note 120starting on page 14.Quote from: biank88 on January 18, 2017, 11:51:33 amIt is one of the things reviewers and marketing tend to ignore. In the later case because it would make their products look bad.