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Original question:

PGA460-Q1: Porblem of returned signal in transformer-driven bistatic mode

PGA460-Q1: Noise at beginning of signal in transformer-driven bistatic mode

Kajetan Dworski
Prodigy 170 points
Part Number: PGA460-Q1

Hello,

I'm trying to drive my transducer in a bi-static mode, and have modified it as described in the FAQ and troubleshooting guide (desoldering the 0-ohm resistor to disconnect TX and RX). Using a multimeter I've confirmed they are separated.

However, the noise at the beginning of the recording stays essentially unchanged. First plot below is TX and RX connected to same transducer, second is with them separate. In these I used the default P1 settings, so very short pulse and gain settings are low as well.

What could be the source of the remaining noise?

  • 0
    TI__Mastermind 27950 points

    Hi Kajetan,

    The burst signal strength still appears as though the driver and receiver are not separated. Do you have access to an oscilloscope to confirm that during burst, the RX-XDCR is not getting excited somehow? A quick way to check this without an oscilloscope is to remove the TX-XDCR, and try bursting. If the saturated burst signal and the object at ~1m still appears with only the RX-XDCR connected, then your receiver is getting excited.

    If everything is truly separated, then the only remaining cause is that the internal driver signal is internally coupling to the receiver path. The driver signal switching noise coupling onto the receiver path is a known problem in bi-static, but it typically does not result in what looks like a mono-static saturated burst. You can try reducing your time varying gain level to be lower during burst (instead of 58.5dB, shift down to 40dB for the first 1ms).

    You can see a working example of a bi-static echo data dump in this old E2E post here, where the electrical internal coupling still appears (non-saturated), and allows for the real acoustic echo signals to still have a larger peak amplitude for very close range object detection: https://e2e.ti.com/support/sensors/f/1023/t/638088?BOOSTXL-PGA460-How-to-decouple-RX-and-TX-signal-path-in-bi-static-mode-

    I have also previously checked that the Murata MA58MF14-7N does work similarly in a bi-static transformer driver mode.

  • 0 in reply to Akeem Whitehead
    Prodigy 170 points

    Hi Akeem,

    Below is what I get with just the RX connected. I will confirm with a scope when I have access to it, but it seems you're right about the internal coupling.

    Will test out lowering the TVG for the 1st ms as well.

    Kai