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Visitor seyhan
Visitor
4,274 Views
Registered: ‎01-22-2012

Analog Capture Circuit in Spartan3c1600E

 Hi, i try to use Analog Capture Circuit on the Spartan3c1600E which gives 14 bit 2's complement value for analog input.

 Its datasheet is  http://www.digilentinc.com/data/products/s3e1600/ug257.pdf.

 Before ADC starts to work, GAIN value should be sent to PreAMP of ADC.

 I try to send 8'b00010001 and expect to set ADC to accept analog input varying 1.25V around 1.65V.

 When i check the audio output of my notebook, i saw that its output voltage varies 1V around 0V.

 

 I apply  cpu's audio output to ADC, with adding an offset voltage of 1.65V   as told in datasheet and it varies 1V.

 According to the datasheet, i should have get 0 digital value when there is no sound coming from my computer which means the voltage applied to ADC is 1.65V.

 But when i check the output i see that LSB 7 bits of the output data are not equal to zero which have to be.

 I can get the sound from DAC whose input  comes from ADC  when i use the MSB 7 bits of 14bit digital  output of ADC.

 Another point is when i apply the output of the sound output of computer without adding any offset voltage so that it varies around 0V, i can get the sound properly. 

   Which one is the right mode to work adding 1.65Voffset or not?

   Is there anything different to be done about Setting preAMP gain so that i can get 14'b0000..0000 output from ADC's    output?

  thank you. 

 

 

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2 Replies
Instructor
Instructor
4,267 Views
Registered: ‎07-21-2009

Re: Analog Capture Circuit in Spartan3c1600E MicroBlaze Development Kit

 I try to send 8'b00010001 and expect to set ADC to accept analog input varying 1.25V around 1.65V.

 When i check the audio output of my notebook, i saw that its output voltage varies 1V around 0V.

 

It might be much easier to troubleshoot your design if you approach the debug process a bit differently.

 

First, with an oscilloscope, measure the peak amplitude of the notebook audio output.  Then provide a DC level which corresponds to this measured peak level on J7 pins, the inputs to the LTC6912 programmable gain amplifier.

 

Adjust the LTC6812 gain settings to provide suitable levels to the inputs of the LTC1407 ADC.  With an oscilloscope or multimeter, you can measure the  LTC6912 output, and watch it change in response to different LTC6912 gain settings.  Use this measurement point to debug your SPI code which programs the LTC6912.

 

Once you have confidence that you have configured the LTC6912 correctly, it will be much easier to make sense of the LTC1407 ADC readings.  Using the same DC levels on header J7, read the LTC output data values for both peak (DC) level and GROUND level applied to J7.

 

If you can read (and understand) the LTC1407 ouput values with these DC levels applied, you should have no problems reading the "live" sampled data using the laptop audio output as a signal source, as long as the signal amplitude is within the bounds of the DC levels you used for testing and setting and verifyying LTC6912 gain.

 

-- Bob Elkind

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Visitor seyhan
Visitor
4,237 Views
Registered: ‎01-22-2012

Re: Analog Capture Circuit in Spartan3c1600E MicroBlaze Development Kit

hi i got over this problem and now i can send a sinus wave to ADC and take a sinus wave which has the same period with the input one.

i found this datasheet http://www.xilinx.com/products/boards/s3estarter/files/s3esk_picoblaze_amplifier_and_adc_control.pdf which explains how the ADC  used and makes it easier.

Thank you help,

 

seyhan

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