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TDC1000-Q1: Delay Time between RX Signal and Stop signal

Songzhen Guo
Intellectual 2840 points
Part Number: TDC1000-Q1
Other Parts Discussed in Thread: TDC1000, TDC7200, TUSS4470

Hi Team,

There is a big customer use TDC1000-Q1.

Several signal was used to trigger ultrasonic device. Customer use several sine wave signal to calculate the time.

The Echo Qualification Threshold level was set to -50 mV. They find that the delay time between LNAOUT and STOP are different. Sometime the second sine wave trigger the Stop, sometime the third sine wave trigger the Stop. See the picture below.

Customer copied the schematic of TDC1000EVM. They also tried on the EVM of TDC1000. It has the same problem. Could you check it for us? I appreciate it if you can help.

 


Second Sine Wave trigger the STOP:


The Third Sine Wave Trigger the Stop:

 

BR

Songzhen Guo

  • 0
    TI__Mastermind 27940 points

    Songzhen,

    The missed stop pulse is a known device issue on the TDC1000. We are referring to this device issue as the TDC1000 lobe shift, and can be summarized as follows:

    Expected Operation: The expected operation is for a STOP pulse to be generated on the first zero crossing following a crossing of the programmed threshold
    Lobe Shifting Event Error: A lobe shifting event occurs when there is more than one STOP detected by the TDC1000 in multi-echo mode. The device functions as expected for the single mode or first STOP, but on the second pulse, a STOP is not generated until the second zero crossing after the signal exceeds the threshold.
    Our recommendation to compensate for this error is to capture multiple time-of-flight measurements, and average the result. For example, the TDC7200's multi-cycle averaging mode can be used to help compensate for the the lobe shift of the TDC1000's. In the TDC7200's Multi-Cycle Averaging Mode, the TDC7200 will perform a series of measurements on its own and will only send an interrupt to the MCU (for example, MSP430, C2000, etc) for wake up after the series has been completed. The number of averaging cycles should be selected (1 to 128). This is done by programming the AVG_CYCLES bit in the CONFIG2 register. Maximizing the number of TDC7200 cycles is our suggested workaround for the TDC1000's side lobe event error.
  • 0 in reply to Akeem Whitehead
    TI__Intellectual 2840 points

    Hi Akeem,

    Thank you so much for you feedback.

    After talked with customer in the morning. we find that the delay time is related with liquid:

    When customer use TDC1000-Q1 to test water, the Stop is fine, it can be triggered at the first zero crossing sine wave. When we change the water to Urea, the Stop signal has Lobe Shifting Event Error. And the the Stop signal is always triggered at the second sine waveform. So customer can't use multi-Cycle to compensate the error.

    Could you check it for us? Could you tell us why TDC1000-Q1 has Lobe Shifting Event Error? Thanks.

    BR

    Songzhen Guo

  • 0 in reply to Songzhen Guo
    TI__Mastermind 27940 points

    Songzhen,

    The lobe shifting event error is a device bug, and only a form of post-processing based averaging can be used to compensate for the error.

    If this bug is preventing them from using the TDC1000 device, they may need to consider using an alternative device, such as the TUSS4470, which will support transducers up to 1MHz. See section "4.2.3 Fixed Gain at High Frequency" of the Logarithmic Amplifier for Ultrasonic Sensor Signal Conditioning for a comparison of the TDC1000 and TUSS4470 at 1MHz for a liquid based measurement.

    The TUSS4470 has an echo interrupt pin (pin O4) which combines and toggles similarly to the operation START and STOP pulses of the TDC1000.