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Digital Analog converter for resonator circuit

Hi I have dual resonator circuit consists of Inductors, capacitors and resistors. I am generating sine wave with amplitude of 1 from DAC and write a frequency sweep function in Matlab however I only get a single resonator response and I am missing the second peak. when I connect 1 ohm or any value less than that in parallel with DAC I am able to get both peaks. I can also get both peak when I am not connecting any resistors in parallel with DAC but I changed the amplitude of my sine waves to 0.02 or less.

What do you guys think is causing this problem that I cannot get both peak with sine wave amplitude 1 with no resistors in parallel ?

DAC has output impedance of 0.5 ohm

current driven =5 mA overdriven current =20mA

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Reply to
chess
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How about a schematic of both connections?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

It sounds like the output impedance isn't really 0.5 ohm, or isn't 0.5 ohm at the frequency of your missing peak.

Read the data sheet carefully -- if they say 0.5 ohm _at DC_ that'll be a big clue.

--
www.wescottdesign.com
Reply to
Tim Wescott

Including the DAC part number.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

single

it says output coupling=DC and output impedance is 0.5 ohm.How can I upload image here?

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Reply to
chess

If the DAC is commercially available, it will have a part number and a data sheet. The data sheet will be available on the manufacturer's web-site.

Post the url/link to the datasheet. Here's an example of such a link

formatting link

It was at the top of the Analog Devices bipolar DAC page and is only an example.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

and

and

1

get

sine

both

be a

data

This is the DAC datasheet

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Reply to
chess

connect

0.5

This is also the my current DAC I am using

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Reply to
chess

A schematic of your circuit please. Could be an LTspice file. Or a scribble with picture uploaded to a image hosting site. and link.

Maybe you are sweeping too fast through a narrow resonance?

George H.

Reply to
George Herold

single

ohm

in

or

no I am not sweeping fast. The peaks should be apart by 5KhZ and my step size for frequency sweep is 100 Hz.

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Reply to
chess 

--
1. Even though the output of the DAQ (Data AcQuisition system) may be 
a DAC (Digital to Analog Converter) DAQ is not a DAC.  

2. You may want to: 

A. Capture an image of your schematic and post it to a web page 
somewhere, or to alt.binaries.schematics.electronic. 

B. Redraw the schematic using LTspice and post the circuit list 
(.asc textfile) here. 

3. As requested previously, please show the connections between the 
DAQ output, your circuit, and the DAQ input. 

John Fields
Reply to
John Fields

AD9142A.pdf

The rule of thumb for data sheet specifications is that if they don't say, then either they don't know or they don't care (or they're embarrassed).

Since you don't have a graph showing output impedance as a function of frequency, then pick one of don't care, don't know, or are embarrassed.

You may be able to ask NI for clarification -- sometimes they're good about answering questions like that, sometimes they're not.

I suspect that the "DAC" is actually a DAC followed by an op-amp stage, and op-amp stages like that tend to have output impedances that rise with frequency.

If you have a signal generator that's got a known-good 50 ohm output up through your second resonance frequency, you can measure the DAC output impedance: just turn it on, set it to an output value, clip the signal generator onto the thing (pay attention to current and voltage limits), and sweep the signal generator frequency through the critical range. You should know the voltage divider equation, which will tell you the output impedance at any given frequency.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

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