Frequency Response Curves (Bode Plot) using an Oscilloscope and Function Generator
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- เผยแพร่เมื่อ 16 ก.ย. 2018
- In this video, we show how to use the automated Bode Plot feature of the SIGLENT SDS1004X-E series of four channel oscilloscopes to create a frequency response curve.
This video applies to the SIGLENT SDS1104X-E and SDS1204X-E oscilloscopes as well as the SDG X series (SDG1X, 2X, and 6X) of arbitrary waveform generators. - วิทยาศาสตร์และเทคโนโลยี
The Bode Plot function is currently available on SDS1104X-E, SDS1204X-E, SDS2202X-E, and SDS2352X-E oscilloscopes.
Can't imagine i'm doing thing all in manual back 17 years ago. An I pass this paper. Gonna get this scope. Damn good
Hi Semut. I know. In many ways, we live in "the future"! There was an additional upgrade to the Bode II functions in the latest firmware. Here is a link with more info: www.siglenteu.com/application-note/power-supply-loop-response-bodeii/
Hi @SiglentVideo. Is it correct to connect SDG to the DUT via a T-piece and then to the oscilloscope? This would allow second output of the SDG to be used for other purpose. This configuration will also tell the oscilloscope the real value of the voltage on the input of a DUT. The presented connection method actually separates what DUT actually sees from what oscilloscope is presented by a separate channel.
How do you manage the cable lengths correction, as a calibration procedure? If no correction available, do we need to use identical length/loss cables on the two channels paths ?
im new to scopes and just got the 1104x-E and saw you had 50ohm terminator. i do know that i saw that you could switch between with the higher end scopes but had no idea that its something i can just put on the end of the cables for matching stuff being tested. so is 50ohm one of the common ones that i should have with this scope for bode testing? also is there others that may be needed? or is it just because it was something that plugged right into the coax cables? what if i want to test input vs output on amps or something how would i know if i need to use a different ohm termination?
Hello Sneakywinja. Jason from SIGLENT NA here. Thank you for writing. 50 Ohms is the typical impedance for most power and RF circuits. Function generators are also typically 50 ohms. To minimize reflections and optimize energy transfer, you want the impedances of all circuit elements to be as close to the same value as possible. Check the impedance of the devices you wish to measure and try to get cables and terminations that match.
Nice demonstration but I have some question. Why you using second output of signal generator? Why not just splitter at the input of filter and 10 MEG oscilloscope probe? If we imagine that input impedance of the filter changing with frequency it will cause changing amplitude on input while sweeping. But when we using second output of sig gen as source of information we "see" constant amplitude which can be not correct for real filter input amplitude. It would work 100% right only if filter have constant and known input impedance. It also OK if we interesting only for responce of the circuit from voltage source with constant output impedance.
Hello. Jason @ SIGLENT North America here. Thank you for writing in. I didn't use a splitter because I didn't have one and suspected that many customers would also be in a similar position. The use of the other output of the SDG is very convenient (it's already there.. no additional purchase required). For some installations, you may be correct.. but, in real use cases, the filter is connected to a single signal source (like an SDG) and there is no splitter involved. It would be an interesting comparison..
@@SiglentVideo Thank for fast answer, Jason! I thought about that task a little bit more and came to decision that in real designing procedure knowledge about output responce irrespective exact input voltage even more applicable than "academic Bode' ("gain vs frequency" not "out amplitude vs frequency"). Because in real circuits we have some source which more close to bench signal generator and have approximately constant output impedance. Thus real signal source have not opportunity to adjust own parameters to filter's input impedance, therefore "Bode in gain terms" will be even more far from true response in real circuit which we interested in first order. I had this question because when I doing some measuring with quartz filters I see how voltage on filter's input significantly drop on some frequencies. I hope I was clear enough. Best regards!
Great video! @1:01 what will be the Oscilloscope "Set Channel" settings for this circuit? I'm afraid you didn't show it on the video. Is Ch2 going to be the DUT Output, and Ch1 will be DUT Input? Or is it the other way around?
I am glad that you found the video helpful. At 1:01, the CH1 FG output goes directly to CH1 scope in. This is the reference channel. To put it another way, FG CH1 is the same as the DUT input.
CH2 of the FG goes through the DUT and then to CH2 of the scope. It is the DUT output.
If you have additional questions, you can write info@siglentna.com
- Jason, SIGLENT North America
@@SiglentVideo Got you. I've been testing this feature atm. I have the newer firmware on my SDS1104X-E and its now called Bode Plot II.
I noticed that the operation will not stop even after finishing the frequency sweep. The AWG sweep goes right back to the "start frequency" and start a new cycle again. Is this the right behavior or its just on my scope? So I have to manually press the stop button to stop the plotting operation?
@@losaminos59 Yes. You have to manually stop the sweeping. - Jason, SIGLENT NA
Nice! Is bode plotting also available with SDS2304X with the SDS-2000X-FG option?
No. The Bode Plotting is not available with the SDS2000X series. It is available with the SDS1xx4X-E and SDS2xx2X-E series scopes:
I got the SDS1104X-E oscilloscope. Do I need this particular signal generator to use the bode plot function in this way?
Hello.
Bode plotting with the SDS1104X-E, SDS1204X-E, SDS2X-E Series, and SDS5000X scopes require a SIGLENT SDG function generator or the SAG and associated license for external USB function generator control.
siglentna.com/waveform-generators/
siglentna.com/product/external-arbitrary-waveform-generator-2/
If you have additional questions, please write info@siglent.com
Have a great day.
Sincerely,
Jason, SIGLENT NA
Since the data rate is split between channels 1/2 and 3/4 on the scope, would there be any benefit to hooking to the scope on channel 1/3 to get the plot to update faster? Or is this a function of the generator and the sweep speed?
The majority of the test time for the Bode application consists of the USB communications to the generator and the ranging function of the scope. The scope data collection time is small in comparison. I don't think you will see any performance increase by splitting the channels. - Jason, SIGLENT North America
Hi, does this work with the SDG1025? (no X) do I need to purchase any software options?
Yes. It should work with the SDG1 family without any additional purchases. The Bode Plot interface is included with the 4 channel SDS1xx4X-E scopes as well as the SDS2X-E scopes. The setup and control interface for all of the SDGs and SAG is as shown in the video. -Jason, Siglent NA
Two questions: Early in the video I saw HiZ selected. I realize this just affects the displayed voltage on the ARB but wouldn’t 50 Ohm have been more appropriate for your properly impedance-matched setup? Or was that immediately overridden by USB commands from the scope anyhow?
Also, what type of USB cable and which USB ports. Would I need to find an A to A cable?
Thanks!
Hi Sidlinger. Jason here. The XE scopes do not have 50 ohm input selection. There are 50 ohm feedthrough adapters used on both scope input channels to help match the impedance of the generator. This minimizes reflections. The 4 channel XE models have an extra USB connector on the rear panel so a standard USB cable (Type A-B) will work. You can write info@siglent.com if you have additional questions.
@@SiglentVideo I think he means your choice of presumed attached impedance. If you set the ARB to Hi-Z it assumes whatever you peck on the screen is at the output, if you set it to 50 it will read in adjusted values presuming that your terminating impedance is actually 50 ohms and to whatever extent they're perfectly matched the voltage will be cut in half. Given you set both sides the same and you're displaying in dB however it's not going to matter...
@@JamesReedy Yes. The correct output selection for the generator would be 50 ohms so that the set voltage values are correct and to use 50-ohm feedthroughs on the inputs to minimize reflections.
I can't remember if the Bode setup reconfigured the generator for 50-ohms or not, but it should be.
Thanks for checking.
- Jason, SIGLENT North America
@@SiglentVideo I seriously hope that the Bode setup doesn't automatically reconfigure the function generator for 50 ohms output because I want to use 75 ohms. Hopefully the function generator outputs can still be set to Hi-Z. I can then use a pair of 75 ohm feedthrough adapters to set the source channel impedances, while using a further pair of 75 ohm adapters at the oscilloscope inputs. Despite the resulting handful of thru terminations this is, for me, still a simple way to roughly measure S21 and S12 for an RF device.
On second thoughts it looks like I need a pair of 50 to 75 ohm adapters to change the outputs of the function generator from 50 to 75 ohms. From the ongoing discussion it looks like the output impedance of the function generator is always 50 ohms. Got confused there.
at 2:14 you say that this bode plot feature works with the sdg1xxx-x, sdg2xxx-x and sdg6xxx-x series function generators.
Doesn't it work with the SDG805/810/830 series function generators?
Yes. It does work with SDG8s running current firmware revisions as well.
So you can do this with SAG1021 AWG also? Can I measure 20hz-20khz audio signal from amplifier circuits?
Yes. The SAG1021 can perform the sourcing function of the Bode plotting feature of the X-E scope. The Bode plot function operates from 10 Hz up-to 25 MHz and should be perfect for your application. If you have additional questions, you can always send an email to info@siglent.com
@@SiglentVideo Just one more question, if I get SDG1032X do I need to get a separate licence for my scope to use this automated bode plot feature? Thanks.
No. The 4 channel X-E oscilloscopes come with the Bode Plot function. To perform a Bode Plot, you just need a signal source. The 4 channel X-E can control the SIGLENT SAG1021 (which requires both hardware and the software activation key.. SDS1000X-E-FG) or one of the SDG X series generators (SDG1000X, 2000X, or 6000X). f you have an SDG X series generator, you can simply connect as shown in the video. No software license needed.
how did you connet the scope and the signal generator, so you gain control over the signalgenerator.
The scope communicates with the generator via a USB cable. - Jason, SIGLENT North America
Is this automated Bode Plot feature available with SIGLENT SDS2101x oscilloscope?
Hi Krish. It is only available with the four channel X-E scopes (SDS1104X-E and SDS1204X-E) at this time.
Hoping this feature available with the next firmware release of SDS2XXXx oscilloscopes, Thanks
@@SiglentVideo Your customers are STILL waiting for the firmware to be be updated on their SDS2000x 4ch oscilloscopes to support Bode plots.
Please don't just take our money then abandon us.
@@MaxWattage Hi Nicholas. Jason @ Siglent here. Thank you for writing. Unfortunately, the SDS2X is unlikely to ever get Bode due to hardware limitations. It is not as simple as adding that feature in code. There has to be enough memory, etc.. and Bode was also never planned nor advertised for the SDS2X platform. Thank you for writing. You can also contact us by writing info@siglent.com
It would also be fairly straightforward to build an application that performs Bode plotting using a computer and the remote control SCPI commands for the scope. Write in if you'd like more guidance on that process.
Does this work with the SDG810 ?
I guess I can answer myself! SDG810 does in fact work. Just need a splitter on the output as it only has a single output.
Why the heck can't I do Bode plots on my more expensive Siglent SDS 2304X, 4ch oscilloscope with built-in waveform generator?
The hardware already has everything built-in needed to do this, all it would take is a software update!
The oscilloscope won't display in Bode plot mode, and the built-in waveform generator won't output a frequency sweep function. Both are purely software limitations.
It's not even available as an add-on licensed feature!
Please please add this to the firmware.
Hi Nicholas. Jason @ Siglent here. I appreciate and understand your rationale, but it isn't likely that Bode is going to be added to the SDS2X family. Software is not the only consideration, as there are hardware (memory) constraints and "room" for futture firmware changes that need to be balanced. If you have additional questions, you can write info@siglent.com.
Siglent Technologies
It would also be fairly straightforward to build an application that performs Bode plotting using a computer and the remote control SCPI commands for the scope. Write in if you'd like more guidance on that process.
Can the list be stored as csv -file to an USB-stick?
Hi Erika. Jason @ SIGLENT North America here. Yes. You can save the Bode data as a CSV to USB as well as copies of the curves as a picture file.
@@SiglentVideo Please make more content like this, I loved it and I would like to educte myself and my students on using this oscilloscope better
Sure, I'll just run a side Bode plot business with a SDG 6052x generator, which costs 7 times more than the scope.
SIGLENTs Bode solutions are considerably less expensive that other vendors. SIGLENT Bode works with any SIGLENT SDG, not just the SDG6000X.
Today, you could perform Bode with an SDS1104X-E and SDG810 for around $900, total.
- Jason, SIGLENT North America
fg is separate box,,, useless
I'm sorry you feel that way. Standalone generators are actually quite useful and generally feature better specifications than their "in scope" products, but they do take up more bench space. The great thing is that SIGLENT offers both internal and external sources, so you can easily choose what fits your application.