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AFE5832: AFE5832 cannot receive input signals correctly in TGC mode

Baolin Sun
Prodigy 20 points
Part Number: AFE5832
Other Parts Discussed in Thread: TX7332

Tool/software:

Hi,

We are currently using the AFE5832 chip in the design of a handheld ultrasound device. While developing the driver for the AFE5832, we encountered an issue that we hope you can help us resolve.

In test pattern mode (Ramp), our driver functions correctly, as demonstrated in the first attached figure. However, when we switch to normal operating mode, the driver fails to properly receive the input signal, as shown in the second attached figure. We initially considered whether the input signal might be out of range, but our differential input is INP: 1.6V and INM: 1.2V, with no additional input voltage.

In normal operating mode (TGC mode), in addition to the chip configurations used in test pattern mode, we have set the following:

  • TGC mode
  • LNA_GAIN set to 15dB
  • PGA_GAIN set to 21dB
  • Programmable Attenuator gain code set to default (0)
  • Input channel INP set to 1.6V
  • Input channel INM set to 1.2V

Despite these configurations, we are unable to achieve normal operation. Are there any additional chip configurations or settings that we need to adjust to resolve this issue? Your guidance and support in this matter would be greatly appreciated.

  • 0
    TI__Expert 3135 points

    Hi,

    Your input is ac coupled or dc coupled ? 

    What is the adc resolution you had set ? Looks like you had set 10bit resolution with 2s complement format. This means output signal is close to zero .  

    If you give 0.4v signal at input it is definitely going to saturate with set gain of  46dB (gain of 200) . Please try by giving small signal or adjust gain/attenuation so that output is within the limit.  Also I recommend giving 5MHz signal to evaluate as most plots in datasheet are taken at that frequency . 

  • 0 in reply to Sachin H K
    Prodigy 20 points

    Hi,

    Initially, I overlooked the output data format of the AFE5832. However, upon configuring the output data in offset binary format, I successfully resolved the initial output issue.

    But there is still a problem at present.  When there is no input signal, the ADC output generates a regular square wave that overlays the original waveform, as shown in the attached figure.. What could be the likely cause of this issue?

  • 0 in reply to Baolin Sun
    TI__Expert 3135 points

    I would like to know the frequency of this square wave .

    What is the state of inm pin?  When you say no input how is the inp pin state in your board ?

    To figure out source of this problem you can try varying the attenuation /lna gain and observed output fundamental sensitivity to that .  

  • 0 in reply to Sachin H K
    Prodigy 20 points

    The frequency of the square wave is around 0.8M, and the amplitude does not change with the change of LNA gain. INP remains at the default bias voltage of 1.6V for AFE5832, and INM remains at the default bias voltage of 1.2V for AFE5832, using AC coupling. INP is connected to the output of TX7332, but TX7332 is not working at this time.

  • 0 in reply to Baolin Sun
    TI__Expert 3135 points

    This indicates that 0.8MHz signal is not coming from input pin side as it does not show any change wrt to LNA gain. Now the suspect is on digital data separation. How are you separating the dout data to plot ? What is your clock frequency ?