TEST - Agilent MSO7104B Oscilloscope capture rate

[CarlG]

Some measurements made to check how different modes affect the scope capture rate.

Oscilloscope basic specs
-3dB bandwidth: 1 GHz
Sample 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 us
Claimed capture rate: 100 000 wfms/s

Note: Screen width is 10 div ==> "Max theoretical capture rate" = 1/(10x timebase)

Comments
Test 1: only Ch1
Test 2: Ch1 and Ch3 (same column as Test 1; no change in capture rate)
Test 3: Ch1 and Ch2
Test 4: All analog channels
Test 5: All analog + all digital channels
Test 6: All analog + all digital channels + decoding two 8bit buses
Test 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 affect 
the capture rate compared to single channel mode. On the contrary, enabling paired channels (Ch1&Ch2)
actually increases the 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 tested

Used equipment
1) Function generator: Agilent 33522A
2) Timer/counter Stanford research systems SR620
Generator 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 out
Counter gate: 1s

Oscilloscope setting (unless otherwise noted)
Acqusition mode: normal
Horisontal mode: normal
X-position: mid
Trigger: edge trigger, rising edge, 500 mV, holdoff = min (60ns)
Display: vector mode


Capture rate [wfms/s] (rounded down to nearest 100 except for 10us/div --> )
Mode:     Ch1;      Ch1&Ch2   Ch1,Ch2,  +16 dig   + decode  enable    disable zoom,       Theoretical
          Ch1&Ch3             Ch3&Ch4             two 8bus  zoom      trig on             max capture
time-                                                                 glitch> 45 ns       rate [wfms/s]
base      
[ns/div)
0.5       93700     93600     93600     93500     93500     47000     93500               200 M

1.0       74100     93500     93500     93400     93400     47000     93400               100 M
2.0       74100     74000     74000     74000     74000     41500     74000                50 M
5.0       59900     59800     59800     59800     59800     36700     59800                20 M

10        59900     59800     59800     59700     59700     36600     59700                10 M
20        94700     59700     59700     59700     59700     36600     59700                 5 M
50        74200     73400     73400     73300     73300     47200     73200                 2 M

100       62400     53100     53100     53100     53100     42600     53100                 1 M
200       38700     33000     33000     33000     33000     32000     33000               500 k
500       16700     16100     16100     16100     16100     19400     16100               200 k

[us/div)
1         13300     11000     11000     1000      11000     14800     11000               100 k
2         10200     10600     10600     10600     10600     14700     10600                50 k
5          6300      9700      9700      6900      6900      7100     6900                 20 k

10                                                 3650                                    10 k
100                                                 780                                     1 k

[ms/div)
1                                                    60                                   100
10                                                    9                                    10

[EEVblog]

Nice work, great data!

Dave.

[CarlG]

It was harder than I thought to make objective tests of this. Strange that I never learn...

I expected the 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 would decrease when I increased the test frequency And 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 that the signal content may vary the capture rate on 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 rate

Display mode:
- Dot display mode did not change the capture rate

Horizontal mode:
- XY mode did not change the capture rate