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Agilent 54620-61601 LOGIC ANALYZER PROBE CABLE (16 Channel)

Question asked by jselmir on Apr 9, 2014
Latest reply on Apr 9, 2014 by algoss

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Hello,
Our firm has bought oscilloscope: "MSOX3024A Oscilloscope: 200 MHz, 4, Analog Plus 16 Digital Channels".
We perform the measurement signal to the SDRAM in hardware devices that test.
Signals period may be 0.5 ns (10 ^ (-9) second) to 20 ns (10 ^ (-9) seconds).
I have two questions about digital probes which are supplied with the oscilloscope.

1. Which is the maximum of delay from the actual values for displayed signal on the oscilloscope when measured with the digital probes?
2. Which is the maximum delay of the displayed signal relative to the actual signal from the digital probes?

Informations about digital probes are:
"Agilent 54620-61601 LOGIC ANALYZER PROBE CABLE (16 Channels)",
input Z:100 KOhm » 8pF, Max: ±40V

I would ask you if you have the documentation with the answers to these questions in electronic version (pdf, etc.) of the Agilent company that recommend it.

Thank you very much.

Edited by: jselmir on Apr 9, 2014 3:12 AM

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algoss Apr 9, 2014 5:30 AM
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I'm not sure what you are asking.

1. Which is the maximum of delay from the actual values for displayed signal on the oscilloscope when measured with the digital probes?

- Do you mean the delay through the cables, or the channel-to-channel skew? The delay through the cables doesn't matter, since they will all be the same. The channel-to-channel skew, according to the datasheet (available online) is 2ns (typical), 3ns (maximum).

2. Which is the maximum delay of the displayed signal relative to the actual signal from the digital probes?

- I really don't understand this question. Please draw a picture that explains what you mean.

I also saw "Signals period may be 0.5 ns (10 ^ (-9) second) to 20 ns (10 ^ (-9) seconds)."

- This scope isn't fast enough to look at these signals. The digital channels sample at 1GSa/sec (period of 1nsec), and BW of the scope is only 200MHz (as it says on the front of the scope). To look at the signals you are talking about, you need at least 2.5 GHz of BW, and a digital sampling rate of 5GSa/sec, which means a much more capable set of tools.

Al

Disclaimer: For more reliable response, you should consider calling your local Agilent Technical Call Center. The Agilent Forums are monitored on an "as available" basis, and aren't necessarily the fastest way to get technical questions answered.
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- jselmir @ algoss on Apr 9, 2014 6:40 AM
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  Thanks for the reply,
  
  First of all, thank you for the fast response. I will try to be more precise.
  I am recording a Clock signal CLK whose frequency is 132 MHz(Period of 7.57 ns).
  The trouble is that my digital probe does not detect the edges properly. When I record the signal with analog probe the High/Low pulse duration are correctly displayed and have the same duration, but when I use the digital probe it displays a variety of different high and low pulse durations. It looks as if it cannot detect the threshold crossing properly.
  
  Analog (Attach Files)
  Digital (Attach Files)
  
  The trouble is that I can´t use my analog channel because there appears to be a delay between data recorded with a digital probe compared to data recorded with my analog probe. It looks as if the data and control signal are not set before the rising edge of the CLK signal.
  
  However if I record the CLK signal also with a digital probe all data and control signals are set before the rising edge of CLK.
  My questions now are:
  - What is the delay between a signal recorded with a digital probe compared to a signal recorded with an analog probe?
  - In case I need a larger bandwidth, is it possible to upgrade my existing oscilloscope and be able to record signals with higher frequency?
  - Can a new set of digital probes with a smaller capacitance be used to lower Channel to Channel Skew?
  Thank you
  Attachments
  - digital.jpg13.7 KB
  - analog.jpg16.1 KB
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  - algoss @ jselmir on Apr 9, 2014 10:39 AM
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    I am recording a Clock signal CLK whose frequency is 132 MHz(Period of 7.57 ns).
    The trouble is that my digital probe does not detect the edges properly. When I record the signal with analog probe the High/Low pulse duration are correctly displayed and have the same duration, but when I use the digital probe it displays a variety of different high and low pulse durations. It looks as if it cannot detect the threshold crossing properly.
    
    - The digital channels sample every 1 nsec. The edge is displayed at the nearest nsec. Assuming you have a 50% duty cycle on your clock, the displayed time between a rising edge and a falling edge, or between a falling edge and a rising edge, will generally be either 3nsec or 4nsec. A full cycle will generally be either 7nsec or 8nsec. Didgtal channels are not like analog channels. They sample more slowly, and they're no interpolation between the samples.
    
    The trouble is that I can´t use my analog channel because there appears to be a delay between data recorded with a digital probe compared to data recorded with my analog probe. It looks as if the data and control signal are not set before the rising edge of the CLK signal.
    
    - There might be skew between the scope and digital channels, and there will be some uncertainty. You can adjust the skew by attaching the scope probe and a digital channel to the same signal, something with a sharp edge, but lower repetition rate, like maybe 10 MHz. Then adjust the skew on the analog channel to get as close as you can. The reason for the potential skew is that there's no way for the scope to know what scope probes you are using (and how long they are), and what adapter (and maybe additional wires) you have on the end of the digital channels.
    
    What is the delay between a signal recorded with a digital probe compared to a signal recorded with an analog probe?
    
    - See above. There's no way to know, but it can be adjusted.
    
    In case I need a larger bandwidth, is it possible to upgrade my existing oscilloscope and be able to record signals with higher frequency?
    
    - You certainly need higher BW. I doubt that your clock waveform is really a sine wave. You probably need at least 1GHz of BW. That will clean up the analog waveform. To get faster digital sampling, you will have to go to a much faster, more capable scope family, probably the Infiniium, which means a new scope.
    
    Can a new set of digital probes with a smaller capacitance be used to lower Channel to Channel Skew?
    
    - The capacitance of the digital probes has little to no effect on the channel-to-channel skew. Faster digital probes, on the faster families of scopes, do have lower capacitance, but that's for other reasons.
    
    Al
    
    Disclaimer: For more reliable response, you should consider calling your local Agilent Technical Call Center. The Agilent Forums are monitored on an "as available" basis, and aren't necessarily the fastest way to get technical questions answered.
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Agilent 54620-61601 LOGIC ANALYZER PROBE CABLE (16 Channel)

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