TEST - Agilent MSO7104B Oscilloscope capture rate - Page 1
Forum section: electronics / testgear

author: CarlG
author_rank: Regular Contributor
timestamp: January 08, 2013, 09:55:54 pm
content: Some measurements made to check how different modes affect the scope capture rate.Oscilloscope basic specs-3dB bandwidth: 1 GHzSample rate: 4 GSa/s (Ch1&Ch3 on); 2 GSa/s (all channels on)Max Memory depth (real time mode): 2 Mpts (Ch1&Ch3 on); 1 Mpts (all channels on)Min trigger re-arm time (segmented mode): 8 usClaimed capture rate:100 000 wfms/sNote: Screen width is 10 div ==> "Max theoretical capture rate" = 1/(10x timebase)CommentsTest 1: only Ch1Test 2: Ch1 and Ch3 (same column as Test 1; no change in capture rate)Test 3: Ch1 and Ch2Test 4: All analog channelsTest 5: All analog + all digital channelsTest 6: All analog + all digital channels + decoding two 8bit busesTest 7: All analog + all digital channels + decoding two 8bit buses, and zoom mode (zoom to 500 ps/div)Test 8: All analog + all digital channels + decoding two 8bit buses, trigger on glitch > 45 ns- 100k wfms/s was not acheived on the DUT in this setup; max measured was 94700 wfms/s- Running two or four channels, adding 16 digital channels, decoding of two 8bit buses does not affectthe capture rate compared to single channel mode. On the contrary, enabling paired channels (Ch1&Ch2)actuallyincreasesthe capture rate! This is probably related to the lowered sampling rate.- Trigging on "Glitch > 45 ns" does not affect the capture rate.- Zoom mode decreases the capture rate at high timebase settings, by up to near 50%, but(surprisingly) increases the capture rate at low settings!- Decoding of analog channels not tested.- Display dot mode not testedUsed equipment1) Function generator: Agilent 33522A2) Timer/counter Stanford research systems SR620Generator output terminated in 50 ohm.Trig out terminated in 50 ohm.Function generator setting:10.000 MHz square wave, 50%, 1 Vpp(10 MHz was chosen to be able to make the same test on scopes with higher capture rate.)Counter connected to Trig outCounter gate: 1sOscilloscope setting(unless otherwise noted)Acqusition mode: normalHorisontal mode: normalX-position: midTrigger: edge trigger, rising edge, 500 mV, holdoff = min (60ns)Display: vector modeCapture rate[wfms/s] (rounded down to nearest 100 except for 10us/div --> )Mode: Ch1; Ch1&Ch2 Ch1,Ch2, +16 dig + decode enable disable zoom, TheoreticalCh1&Ch3 Ch3&Ch4 two 8bus zoom trig on max capturetime- glitch> 45 ns rate [wfms/s]base[ns/div)0.5 93700 93600 93600 93500 93500 47000 93500 200 M1.0 74100 93500 93500 93400 93400 47000 93400 100 M2.0 74100 74000 74000 74000 74000 41500 74000 50 M5.0 59900 59800 59800 59800 59800 36700 59800 20 M10 59900 59800 59800 59700 59700 36600 59700 10 M20 94700 59700 59700 59700 59700 36600 59700 5 M50 74200 73400 73400 73300 73300 47200 73200 2 M100 62400 53100 53100 53100 53100 42600 53100 1 M200 38700 33000 33000 33000 33000 32000 33000 500 k500 16700 16100 16100 16100 16100 19400 16100 200 k[us/div)1 13300 11000 11000 1000 11000 14800 11000 100 k2 10200 10600 10600 10600 10600 14700 10600 50 k5 6300 9700 9700 6900 6900 7100 6900 20 k10 3650 10 k100 780 1 k[ms/div)1 60 10010 9 10

author: EEVblog
author_rank: Unknown
timestamp: January 09, 2013, 01:20:18 am
content: Nice work, great data!Dave.

author: CarlG
author_rank: Regular Contributor
timestamp: January 13, 2013, 02:37:36 pm
content: It was harder than I thought to make objective tests of this. Strange that I never learn...Iexpectedthe test frequency to affect the capture rate. That's the reason I chose a pretty high test frequency, so that its period was much lower than the scope's minimum retrigger/re-arm time. What I didn't expect was that the capture rate woulddecreasewhen I increased the test frequencyAnd it was consistent, going from 1 MHz up to 30 MHz in 1MHz steps.Then I noticed that even changing the output amplitude of the test signal affected the capture rate: higher amplitude lowered the capture rate. Next, I kept the same amplitude but changed the scope vertical scale, with the same effect: going from 2 V/div to 100 mV/div substantially decreased the capture rate! And yes, turning off all channels gave max capture rate (other settings unchanged).I assumed that only the amount of captured data would have effect (which is automatic on these Agilent scopes), but obviously that's not the case. I'm not sure whether the data processing time increases, or if it's substantially more data to be transferred to the graphics processor, that lowers the capture rate.The conclusion is that when comparing scope capture rates, it seems "fair" to use the Auto setup since so many parameters come into play. However, the Auto setup result may not (or rather typically won't) be the setting you would choose for a typical measurement, which may give an "unfair" comparision, like when comparing scopes with different number of horizontal divisions.Also, it might be worth noting thatthe signal content may vary the capture rateon DSOs, which may be good to know when high capture rate is important.Some additions to the test in the first post (not tested on all settings so there might be exceptions):Acqusition mode:- Peak detect did not change the capture rate- Average mode and high resolution mode lowers the capture rateDisplay mode:- Dot display mode did not change the capture rateHorizontal mode:- XY mode did not change the capture rate