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VCA8500BOARD: default power up mode was lose efficacy

user6022821
Prodigy 40 points

Part Number: VCA8500BOARD

When I used default power up mode by VCA8500, I give it a 500khz 100mv AC signal,then the signal wasn't  amplified,and present a square wave.

  • 0
    TI__Mastermind 49766 points
    Hello,

    Welcome to TI E2E forum.

    A couple of questions.
    1. Do you notice the square wave on all the 8 channels? Can you attach the scope waveforms of the input and the output channels?
    2. Have you tried the PC control mode to control the VCA8500 device functionality?
  • 0 in reply to Praveen Aroul
    Prodigy 40 points

    1.Here is the  input (yellow)and the output(purple) scope waveforms,and 8 channels are identical.

    2.Yes,I have tried PC control mode, the output waveform doesn't change.

    Thanks!

  • 0 in reply to user6022821
    TI__Mastermind 49766 points

    Hi,

    Square wave occurs in cases when the signal chain gain is too high.

    With 20dB fixed LNA gain, 20dB PGA gain, the signal chain gain is 40dB (assuming 0dB attenuation), this would amplify the signal amplitude by 100.

    You may want to reduce the input amplitude and check. 

  • 0 in reply to Praveen Aroul
    Prodigy 40 points

    Hi,

      I've reduce the input signal to ±20mv,but the output signal was still wrong. 

      The first picture is my test bed, did there something wrong?

    Thanks for your reply!

  • 0 in reply to user6022821
    TI__Expert 6040 points

    in your plot, red plot shows about 250mVpp sine signal. make sure the Vcntl signal is applied correctly. 0V is min gain and 1.2V is the highest gain. 

    the setup has a lot of noise due to cables. we suggest you use SMA/BNC cable to minimize the coupling noise. 

    if you input 100mVpp, you can adjust the Vcntl to make the device out put unclampped waveforms. please note VCA8500 has clamp function on the VCA output as well. if signal is too big, the output will be clamped. 

    Thanks!