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PGA970: Output amplitude problem

Part Number: PGA970
Other Parts Discussed in Thread: USB2ANY

Hi!

I have a problem with wave generator. At 1Khz, I have good amplitude, but at 5Khz amplitude is about 500mV, about half as much. Skip filter is enable and nothing is connected on P1 and P2.I measure my signals directly on P1 and P2 (Vcc = 3.55V).

Is it normal?

Thanks in advance.

Didier


  • Hi Didier,

    Do you notice the same problem at different VCC voltages? Does the voltage decrease linearly, or does it lower at a certain frequency?

    Regards,

  • Hi,

    My problem come from Filter between PE and PI, Enable or desable skip filter does not  change something (I don't understand why).

    I have connected directly PE and PI and all works fine.

    Regards.

    Didier

  • Hi Didier,

    Are you working from the EVM, or from your own board? On the EVM the lowpass filter between PI and PE should not be populated by default. The skip filter function only controls whether the PI and PE pins are connected internally, so it will not have an effect if the PI and PE pins are shorted externally as well.

    If you are working from your own board with a lowpass filter populated between the PI and PE pins, then there may be an issue with how you are setting the skip filter function. If you are using the GUI, after setting the skip filter bit in the ADC settings page, I would also check the Low Level Configuration page to make sure that the bit is properly set in the LVDT_OP_CTRL register.

    Regards,

  • Hi!

    I am working with EVM and own boad with SPI USB2ANY connector.All seems to works fine except "SKIP FILTER" I use filter with 1K and 100nF (15Khz cut offf), but cut-off seems to be 5Khz. When à connect directly PE and PI, all works fine.

    Regard.

    Didier.

  • Hi Didier,

    There might be a mistake in your filter component selection (or a typo in your response). Using a 1Kohm resistor and a 100nF cap will give you a ~1.5khz cutoff frequency. A 10nF capacitor will give you a 15khz cutoff.


    Regards,