Gw Instek GDS2204E (200MHz 4 channel DSO) review

[CC555]

Hello,

similar problem with I2C  .

100 kHz clock signal, channel 4: SCL, channel 2: SDA, triggering at channel 1 event:

At 2 Ms the oscilloscope is not decoding:


a higher sample rate and it decodes properly:

[tautech]

Wouldn't you normally trigger on the clock ?

[CC555]

Wouldn't you normally trigger on the clock ?

The problem would be the same, when you select 10 Mpts the oscilloscope needs a higher sample rate to decode the signal, if you select less memory it decodes at 2Ms/s iirc (I will try it later).

In this case I want to capture the bus at a specific event in my pcb, so I select the channel 1 to trigger the oscillocope on that event.

Thanks for you reply.

[rhb]

*&#@!!!

I bought an MSO-2204EA precisely for this task!

[nctnico]

I have not heard back from GW Instek's technical support in the EU but I'm pretty sure they are closed for the holidays.

[CC555]

with less memory the scope decodes at lower sample rates:



but if 10 Mpts is selected:

At 10 MS/s it doesn't decode the signal (clk = 100 khz):


It needs 20 MS/s, that is a 0.5M buffer  :


I don't know if my settings are 100% right but I would say this oscilloscope has a problem decoding serial buses with the memory and sample rates selected.

*&#@!!!

I bought an MSO-2204EA precisely for this task!

Me too, uCs and serial buses.

[nctnico]

I think the firmware engineers at GW Instek cut a corner by skipping (too many) samples when decoding deep memory. This should be easy to fix for them though at the expense of speed.

[rhb]

My SWAG is that it is a consequence of Object Oriented Programming.  Instead of decoding a short buffer and logging data to a long buffer it's trying to decode the entire buffer whatever the size.

I may be wildly wrong as I've not looked into the matter yet.  All I know is what's been posted here.  But I've seen similar effects from OOPS, for example drawing 6 curve traces by drawing 1, erasing it and drawing 2, erasing them and drawing 3, etc.  Looks damn stupid if you're drawing 6-10 curves.  Intelligent users tend to giggle a lot looking at that.

The decoder should be operating on a small window as data comes in.  That window should slide along the buffer as samples come in.  The observed behavior suggests that it is always starting the decoding at the start of the buffer.

This is a clear argument for open source scope application code.

[tautech]

I don't know if my settings are 100% right but I would say this oscilloscope has a problem decoding serial buses with the memory and sample rates selected.

What would concern me more is the displayed signal integrity ? Not so much the scopes ability to portray it but the glitches and the variances in the data idle voltage of ~1/2/div. 

Something's maybe not right with your digital circuit or probing technique.

Jump back out of Decode and see what waveform shapes and amplitude you get then.

[CC555]

Hello tautech,

I think there is not any problem with these glitches, they are real and always show up when clock is low during a communication so It is the slave who is controlling the data line and can generate them.




And I have to check if the decodification is in the right place in the pictures. Anyway I am going to use a saleae logic to decode the bus.

[nctnico]

I don't know if my settings are 100% right but I would say this oscilloscope has a problem decoding serial buses with the memory and sample rates selected.

What would concern me more is the displayed signal integrity ? Not so much the scopes ability to portray it but the glitches and the variances in the data idle voltage of ~1/2/div. 

Something's maybe not right with your digital circuit or probing technique.

Jump back out of Decode and see what waveform shapes and amplitude you get then.

The shape of the signals isn't related to decoding. There are probably resistors between the various I2Cs devices to prevent one part of a circuit blowing up the rest of the circuit (safety barrier). Alternatively the value of the pull-up resistors may be too low so some devices may not sink enough current to pull the I2C lines completely low. Either way I've seen similar I2C signals before.

[tautech]

I don't know if my settings are 100% right but I would say this oscilloscope has a problem decoding serial buses with the memory and sample rates selected.

What would concern me more is the displayed signal integrity ? Not so much the scopes ability to portray it but the glitches and the variances in the data idle voltage of ~1/2/div. 

Something's maybe not right with your digital circuit or probing technique.

Jump back out of Decode and see what waveform shapes and amplitude you get then.

The shape of the signals isn't related to decoding.

If thresholds are set correctly.
Runts like in the middle of this screenshot will throw a cat amongst the pigeons.

[CC555]

Hello tautech, thx for you reply.

I would say those spikes are not important, i2c communication is working properly in my device.

It is a 100 khz clock so I think there is not any signal integrity problem (i didn't measure its rise time), the frequency is too low.

In the end, I am not going to send the oscilloscope back, in the 1000 € range I think is a good choice.

[CC555]

I have not heard back from GW Instek's technical support in the EU but I'm pretty sure they are closed for the holidays.

Hello,

any news from GW Instek?

[nctnico]

I have not heard back from GW Instek's technical support in the EU but I'm pretty sure they are closed for the holidays.

Hello,

any news from GW Instek?

I got a reply saying they are working on it. I have not checked if a new firmware version has been released.

[CC555]

Thx for your reply,

there is a new firmware version, v 1.34

Version 1.34
1.Added a new ¡§Frequency Response Analyzer¡¨ APP function which can be downloaded from our website.
(This APP only available for MSO-2000EA & MDO-2000E series)
2.Updated the Japanese menu tree translations for SA function.
3.Updated the Japanese menu tree translations for digital filter function.
4.Updated the simplified Chinese menu tree translations for some functions.
5.Updated the Russian menu tree translations for DMM function.
6.Fixed the EVENT table display and storage error issue for UART bus decoding.
7.Fixed the window zoom display issue for I2C bus decoding.
8.Fixed the I2C bus decoding error.
9.Fixed the type of executable for DEMO function.
10.Fixed the return value of SA:MEMory SCPI command.
11.Fixed the return value of <x>:MEMory and :DIGital:MEMory SCPI command.
12.Fixed the setting value of TRIG:DEL:LEV SCPI command.
13.The digital filter function can be implemented now after the SEGMENT data caught.
14.The firmware upgrade procedure is now ONLY support the ¡§Safe mode¡¨ firmware upgrading from this firmware version.

[nctnico]

It seems the biggest change is the network analysis feature for the models which have an internal waveform generator. Unfortunately GW Instek didn't fix the oversampling needed for UART decoding 

[DougM]

How well does this 'scope handle input overdrive?

The reason I'm asking is that I quite often want to look at a smallish voltage range of a larger signal. Right now, I've found that my Rigol DS1054Z is truly dreadful in this respect. For example, I have a square wave at 1kHz between 0v and 40V. The Rigol becomes useless at 2v/div let alone at higher gain... (I have some screenshots on the DS1054Z thread). 

Some people may suggest that this isn't a "proper" use of a digital scope, and that I should be keeping the whole signal on the screen and digitally zooming. I, respectfully disagree, and think the input stages should be capable of placing the limited digital resolution on the interesting part of the voltage range. (Especially with only 8 bits of ADC)

That being said, how does the GDS2204E perform in this respect?  I have excellent scopes available at work, but for home use, I think I need something better than the Rigol...

Best regards,
Doug

[nctnico]

I did a test with a 20Vpp 1kHz square wave:



The offset range is specified in the datasheet. At 500mV/div this seems to be +/- 25V. At more sensitive settings (200mV/div and less) the offset range is +/-5V.

[2N3055]

For DS1000Z:

Offset Range (Probe ratio is 1X)

1 mV/div to 499 mV/div: ±2 V
500 mV/div to 10 V/div: ±100 V

As far as I could see, DougM wants to look at part of 40V P-P signal at better than 1V/DIV or less..
No digital scope I know of will have dynamic reserve of 200x of full screen sensitivity... And probably only +-8 to 10 DIVS...

If A/D converter full scale input for instance is 2V, so on 100mV/DIV  input, your scope  full dynamic range is +- 5 DIVS.  DC offset will be only helpful if you have 100 mV AC riding on top of 12V offset, so you dial in offset in opposite direction to "pull it back" to screen.. Or you AC couple it..
If you have 40 V AC P-P, you need 40V dynamic range signal path for it all to fit in. Without mentioning amplification.. That is with unity gain.

I don't know of any digital scope that can do it. If someone know one I would like to learn about it. It would be good info.
Also, no matter how quick they recover from overload, it ain't pretty...

I believe David Hess mentioned sampling scopes (old analog diode bridge types) in other thread.
Diode bridge sampling scope are direct sampling devices. They don't have input amplifiers and are basically S/H circuit that is disconnected from input all the time, except at the very short time of sample window (aperture). By choosing time at which to sample and if needed adding DC offset, you can look at any part of waveform with no problem of overshoot.
They are repetitive sample devices (random or sequential) and are useful only for repetitive and stable signals..

Modern approach to more detail on digital scopes is hi res scopes (more than 8 bit), keeping signal within dynamic range, and zoom in in software.. 12bit scope will have 4x more detail (pixels) in vertical than 8 bit... But, it costs money...

Regards
Sinisa

[nctnico]

For DS1000Z:

Offset Range (Probe ratio is 1X)

1 mV/div to 499 mV/div: ±2 V
500 mV/div to 10 V/div: ±100 V

As far as I could see, DougM wants to look at part of 40V P-P signal at better than 1V/DIV or less..
No digital scope I know of will have dynamic reserve of 200x of full screen sensitivity... And probably only +-8 to 10 DIVS...

That depends entirely on how the input circuit is designed and it is not 200x but 5x (40V/8V full display range @ 1V/div = 5x). If the oscilloscope allows a large offset then the input circuitry should be designed to handle a signal which swings between the maxima of the offset. It seems the Rigol has a design flaw and thus has overdrive problems.

[2N3055]

That depends entirely on how the input circuit is designed and it is not 200x but 5x (40V/8V full display range @ 1V/div = 5x). If the oscilloscope allows a large offset then the input circuitry should be designed to handle a signal which swings between the maxima of the offset. It seems the Rigol has a design flaw and thus has overdrive problems.

He said that he would want to look at 10mV/DIV if he could... I simply stated that what he expects is unrealistic.. The fact that other scopes might recover a bit better or will allow one more step on a vertical atten before going crazy is not gonna give him what he wants to do... Every overdriven amplifier have overdrive problem.

Also I really doubt ANY digital scope will have full 5 screens below and above actual screen of dynamic range.. Maybe a screen but not much more.
Like I said, if you know one that has such a great dynamic range I would like to know..

Old CRT scopes had signal path with much higher voltage on power supplies .. That gave them much higher inherent dynamic range.. They were much better in that regard..
On DS1000Z input path is powered by +-5V.. if they used +-15V, followed by limiter to protect A/D converter, it would be much better... I agree. But not much better.
Maybe one more step on attenuator..

Don't get me wrong. I'm not defending Rigol. I would be very interested in a test how other scopes would fare in this respect. I suspect not much better.
How much quantitatively, needs to be tested....

Regards
Sinisa

[DougM]

That depends entirely on how the input circuit is designed and it is not 200x but 5x (40V/8V full display range @ 1V/div = 5x). If the oscilloscope allows a large offset then the input circuitry should be designed to handle a signal which swings between the maxima of the offset. It seems the Rigol has a design flaw and thus has overdrive problems.

He said that he would want to look at 10mV/DIV if he could... I simply stated that what he expects is unrealistic.. The fact that other scopes might recover a bit better or will allow one more step on a vertical atten before going crazy is not gonna give him what he wants to do... Every overdriven amplifier have overdrive problem.

Also I really doubt ANY digital scope will have full 5 screens below and above actual screen of dynamic range.. Maybe a screen but not much more.
Like I said, if you know one that has such a great dynamic range I would like to know..

Old CRT scopes had signal path with much higher voltage on power supplies .. That gave them much higher inherent dynamic range.. They were much better in that regard..
On DS1000Z input path is powered by +-5V.. if they used +-15V, followed by limiter to protect A/D converter, it would be much better... I agree. But not much better.
Maybe one more step on attenuator..

Don't get me wrong. I'm not defending Rigol. I would be very interested in a test how other scopes would fare in this respect. I suspect not much better.
How much quantitatively, needs to be tested....

Regards
Sinisa

No, I don't think I asked for 10mV per box (though that would be excellent!).  With a 10x probe the Rigol can only handle 5V/div on a 40V pkpk signal, which is very disappointing. (I will try with the probe at 1x later today and see what I can do).

I'd like better than 1V/division for sure, and 100mV would be nice. I'm coming to realize that this may not be a very mainstream use case.

Doug

[2N3055]

No, I don't think I asked for 10mV per box (though that would be excellent!). 

No you didnt, but I kinda figured you would like it :-))

I'm coming to realize that this may not be a very mainstream use case.

No it's not so much. But it would be very useful.  On several occasion during years  I wish I had a scope that could do that....

Regards,

Sinisa

[tautech]

For DS1000Z:

Offset Range (Probe ratio is 1X)

1 mV/div to 499 mV/div: ±2 V
500 mV/div to 10 V/div: ±100 V

As far as I could see, DougM wants to look at part of 40V P-P signal at better than 1V/DIV or less..
No digital scope I know of will have dynamic reserve of 200x of full screen sensitivity... And probably only +-8 to 10 DIVS...

That depends entirely on how the input circuit is designed and it is not 200x but 5x (40V/8V full display range @ 1V/div = 5x). If the oscilloscope allows a large offset then the input circuitry should be designed to handle a signal which swings between the maxima of the offset. It seems the Rigol has a design flaw and thus has overdrive problems.

Yep, the devil is in the detail.
For the new Siglent X-E series:

Offset ranges 1x input.
500uV~118mV/div: ±2V
120mV~1.18V/div: ±20V
1.2V~10V: ±200V/div

2V/div will give sufficient offset for DougM's needs and using the minor divisions ~250mV resolution.