How to generate a high-precision sine source for ad test?

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wateror

Joined: 26 Aug 2007
Posts: 81

12 Mar 2009 3:43 sine source

I need to test a 16bits ADC, but I don't have the proper sine source?
Is there any idea?

Mehdi1357

Joined: 18 Jan 2008
Posts: 25
Helped: 1
Location: the Earth

16 Mar 2009 9:14 precision sine wave generator

hi
There are many different ways to generate a precision sine wave , but by using a DDS (direct digital synthesizer) you can achieve your goals. That’s an effective and inexpensive way.
A basic DDS circuit consists of an electronic controller, a random access memory, a frequency reference (usually a crystal oscillator), a counter and a digital to analog converter (DAC) all these are gathered in a small chip.
I suggest you to use AD9834 and so on, The AD9834 is a 75 MHz DDS device capable of producing high performance sine and triangular outputs. The AD9834 is written to using a 3-wire serial interface. This serial interface is compatible with DSP and microcontroller standards.
See data sheet for more information
Very Happy

dmilosd

Joined: 19 Mar 2009
Posts: 2

26 Aug 2009 19:00 ad9834

I know that I am out of date, but isnt this AD9834 a way too bad to characterize 16bit ADC??? We are talking about ~96db SNR and SFDR (if the adc is good) of smaller than 100dB or I missed something?

Regards,
Milos

Petre Petrov

Joined: 05 Aug 2009
Posts: 51
Helped: 5
Location: Sofia

26 Aug 2009 20:28 bandwidth generating test

Hello!
You should specify at least:
* needed accuracy
* test frequency
* parameters of the ADC to test
* the tests methods and goals
If you wish an accuracy up to approximately 10 bits you could you use the methods in:
http://www.national.com/an/AN/AN-263.pdf
But there is no easy solution if you need 16 bits accuracy +-0.5LSB
May be the only solution is to use industry standard source from the best manufactures.
It that case you are in need approx 18 bits accuracy of the generated test signals.
BR

rfsystem

Joined: 25 Feb 2002
Posts: 858
Helped: 96

26 Aug 2009 23:11 high precision signal generator

If on the edge of technology it could mean a 100MS/s 13-14 ENOB 16bit ADC

Which source generate 15-16bit ENOB at 50MHz ???

I think all ADC's are testet wich high purity generators with less than -50dB spurs which are passive filtered down further. there is no instrument to my knowledge.

But others should prove that I am wrong.

eecs4ever

Joined: 31 Jan 2006
Posts: 181
Helped: 26
Location: Analog Environment

27 Aug 2009 3:10 high precision adc test

Maybe try cascading multiple bandpass filters after your signal generator.

http://www.krfilters.com/bandpass%20filters.htm

Petre Petrov

Joined: 05 Aug 2009
Posts: 51
Helped: 5
Location: Sofia

27 Aug 2009 8:38 how to generate sin wave

It depends on test goals and available resources.

There are relative cheep solutions, eg.
http://www.valuetronics.com/Details.aspx?Model=BK%20Precision_3003&ProdID=2688
http://www.testequipmentdepot.com/bk-precision/signal-generators/4017b.htm
http://focus.ti.com.cn/cn/lit/an/spra007/spra007.pdf
and many others.

I am sure you could find several solutions after you precise your task., but in all cases a test bench for quality testing of 16-bits devices is not an easy and cheep task.

Also pay attention to home made amplifiers and filters.
Usually they are not suitable for testing 16-bits devices.

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27 Aug 2009 8:38 Ads

wateror

Joined: 26 Aug 2007
Posts: 81

02 Sep 2009 10:17 how to adtest

thanks. The bandwidth of my AD is 50kHz. I tried to use a forth order active bandpass filter to filter the output of an sine wave generator (which is only 70dB snr). But it ended up in getting worse distortion then. I am trying to test it with an Agilent ATE system. Its spec shows that it can reach 24bits accuracy. I hope it will work. Thanks all.

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

02 Sep 2009 10:51 adtest how to

Quote:

I tried to use a forth order active bandpass filter to filter the output of an sine wave generator (which is only 70dB snr). But it ended up in getting worse distortion then.

It's necessary to use high quality, high GBW OPs for the filter. Passive filters may achieve low distortion more easily, if you don't worry about manufacturing the inductors by hand.

Petre Petrov

Joined: 05 Aug 2009
Posts: 51
Helped: 5
Location: Sofia

02 Sep 2009 16:31 sine source

Hi!
The term “band width” with ADC has different and sometimes unclear definition with different manufacturer.
The test methods of defining the bandwidth of a “sampler” (ADC) are more or less controversial and not fully explained.
I preferred my own method that states

"If everything else is neglected you could divide the sampling rate Fd at factor of four (4) in order to find the guaranteed bandwidth (-3dB) from your ideal ADC in the worst case sampling of a sine wave without direct current component (DC= 0)."

Example:
With 44.1 kHz sampling rate you have guaranteed bandwidth of approx. 11 kHz.

Also there is a relation between the Signal Sampling Factor N = Fd/Fsmax and the number of the required bits n and this is not fully explained in the publications.

But the subject is complicated and a lot of people will disagree with the written above.
It is really hard to guarantee 16 bits accuracy with 50 kHz sine wave testing especially at low signal levels.
Normally there should be good synchronization between the generator and the sampler and appropriate reference testing system.
Good luck!

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

02 Sep 2009 23:17 howto adtest

What you discuss as ADC bandwidth (e.g. Fs/4) is a property of the sampling process rather than the device.

As a device parameter, the term bandwidth is usually designating the analog bandwitdh of the sampler and can be expected by a factor of 5 - 10 higher than Fs. It gets effective in pulse signal acquisition or undersampling digital receiver systems.

wateror

Joined: 26 Aug 2007
Posts: 81

04 Sep 2009 13:17 dds ad9834

Yeah, actually the SNR will drop as the input signal frequency increases. For the bandwidth I mentioned here, it refered to the Nyquist bandwidth.
I have found some precision sine wave generator on the internet (as stanford ds360), but it's expensive for me. I just wanna some economic way to build a circuit with sine signal output.

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

04 Sep 2009 14:34 How to generate a high-precision sine source for ad test?

A Nyquist bandwith frequency of 50 kHz implies, that your test frequency has to be considerably lower to see distortion in the ADC output, unless you don't go for a two-tone intermodulation test. At frequencies of e.g. 1 - 10 kHz high end audio OPs provide really low THD values, the said passive filter option may be still more easy, however.

Generally, it's always easier to generate a low distortion fixed frequency by a medium quality generator and a specific filter than trying to get the signal from a variable frequency generator directly. It's true in RF and AF measurements as well.

Petre Petrov

Joined: 05 Aug 2009
Posts: 51
Helped: 5
Location: Sofia

05 Sep 2009 21:13 Re: How to generate a high-precision sine source for ad test

FvM : “What you discuss as ADC bandwidth (e.g. Fs/4) is a property of the sampling process rather than the device.”
PP: Yes You are right. This is for the sampling process and with ideal ADC, almost infinite number of bits, etc. But if you add the reality to this ideal situation usually you are getting something worse.
Of course with synchronization, etc. you could get something better, but I am not sure that this is the situation.

FvM : “As a device parameter, the term bandwidth is usually designating the analog bandwitdh of the sampler and can be expected by a factor of 5 - 10 higher than Fs. “
PP: I am not sure that this is a clear and testable from the users point of view.

FvM : “It gets effective in pulse signal acquisition or under sampling digital receiver systems.”
PP:
“pulse” is highly unclear term for me.
“unders sampling” is also meaningless for me. May be you mean with “signal sampling factor” (SSF) N lower than 2?

Wateror :....”Nyquist bandwidth.....”
PP: I am not sure that there is relevant quotation(s) from the paper(s) of H Nyquist concerning any “bandwidth” applicable to sampling, ADC, DAC and signal processing. I cannot find any understanding from the side of Nyquist to these processes.
May be you mean SSF N=2 and the frequency of the 100% amplitude modulation when SS, CS and SBLS are sampled?
If you have F100% = 50 kHz it is good to try 100 times lower frequency.
Try to calculated try frequency using method with amplitude errors from
http://www.ieindia.org/pdf/88/88ET104.pdf
or from
http://www.radiotec.ru/catalog.php?cat=jr4&art=2363
But you should have really flat amplitude characteristic of the tested and testing equipment and a good software. 16 bits means approx +-0.001%?

Wateror : “I just wanna some economic way to build a circuit with sine signal output.”
PP: Again: If you wish an accuracy up to approximately 10-12 bits you could you use the methods in:
http://www.national.com/an/AN/AN-263.pdf
I have tested most of them many years ago and they words very well.
There are something to change of course
But you should specify the technical requirements of the desired solution.

Wateror :... SNR...
PP: This is really difficult and discussion.

FvM: ... of e.g. 1 - 10 kHz ...
PP: May be it is good first to tests into 250-1000Hz range and after that go to to higher frequency.
But how to guarantee the needed 16 bits accuracy of the test bench?

May be if you contact a manufacturer or independent testing firm that will be good.
There is no enough information about your problem.
I hope that will help

wateror

Joined: 26 Aug 2007
Posts: 81

06 Sep 2009 15:20 How to generate a high-precision sine source for ad test?

Thank you, I should try anyway.

dmilosd

Joined: 19 Mar 2009
Posts: 2

07 Sep 2009 9:17 Re: How to generate a high-precision sine source for ad test

wateror wrote:

Hi,

I also used the 4th order active filter, but got quite good results. I used NS LME49720 and LME49600 in order to maintain THD very low. Perhaps you could try with these components? I measured harmonics at -90dBc and before they were at -65dBc. I also had to play around with many parameters like power supply, termination resistors and so on, but it is achievable!

BTW, I would just like to point out, that SFDR is quite hard to measure as you need really a PURE input sine wave (it is easier to measure SINAD).

Best regards,
Milos