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Digital Analog converter for resonator circuit

Started by chess August 10, 2015
On Tue, 11 Aug 2015 11:56:32 -0500, "chess"
<106766@Electronics-Related> wrote:

>>On Monday, August 10, 2015 at 10:04:39 PM UTC-4, chess wrote: >>> 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 mA >>> >>> >>> --------------------------------------- >>> Posted through http://www.Electronics-Related.com >> >>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. > >no I am not sweeping fast. The peaks should be apart by 5KhZ and my step >size for frequency sweep is 100 Hz. >--------------------------------------- >Posted through http://www.Electronics-Related.com
--- 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
On Tue, 11 Aug 2015 09:27:49 -0500, chess wrote:

>>>On Tuesday, 11 August 2015 14:52:13 UTC+10, chess wrote: >>>> >On Mon, 10 Aug 2015 21:04:35 -0500, chess wrote: >>>> > >>>> >> 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 >>>> > >>>> >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 >>>> >>>> it says output coupling&Atilde;&#156; and output impedance is 0.5 ohm.How can I >>>> upload image here? >>> >>>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 >>> >>>http://www.analog.com/media/en/technical-documentation/data-sheets/
AD9142A.pdf
>>> >>>It was at the top of the Analog Devices bipolar DAC page and is only an >>>example. >>> >>>-- >>>Bill Sloman, Sydney >> >>This is the DAC datasheet http://www.ni.com/datasheet/pdf/en/ds-10 >>--------------------------------------- >>Posted through http://www.Electronics-Related.com > > This is also the my current DAC I am using > > http://www.ni.com/datasheet/pdf/en/ds-24
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