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Using TDC100 in new projecto to TOF measuremente in the air with 300khz transducer

Daniel Pozzatti
Prodigy 20 points
Other Parts Discussed in Thread: TDC1000, TUSS4470, PGA460

Hi everyone,

I'm a hardware engineer and I'm working on a board for a new product using the TDC1000 and a 300khz transducer to measure TOF between the transducer and a water plane.
Right now I'm just trying to measure TOF in the air between the sensor and an object but without success.

The circuit I am using is the following:

And I have the following configuration for my TDC:

TX_CLOCK:                         307187.500000 Hz
CONFIG_0
        RAW:                            0x66
        TX_FREQ_DIV:            16
        NUM_TX:                      6
CONFIG_1
        RAW:                            0x40
        NUM_AVG:                   1
        NUM_RX:                     0
CONFIG_2
        RAW:                            0x00
        VCOM_SEL:                 INT
        MEAS_MODE:              TOF
        DAMPING:                    OFF
        CH_SWP:                     OFF
        EXT_CHSEL:               OFF
        CH_SEL:                      1
        TOF_MEAS_MODE:    0
CONFIG_3
        RAW:                            0x04
        TEMP_MODE:             REF, RTD1, RTD2
        TEMP_RTD_SEL:        PT1000
        TEMP_CLK_DIV:         8
        BLANKING:                 OFF
        ECHO_QUAL_THLD:  -220 mV
CONFIG_4
        RAW:                                     0x1F
        RECEIVE_MODE:                 SINGLE ECHO
        TRIG_EDGE_POLARITY:     RISING
        TX_PH_SHIFT_POS:           31
TOF_1
        RAW:                                     0x24
        PGA_GAIN:                           1 dB
        PGA_CTRL:                          ON
        LNA_CTRL:                           ON
        LNA_FB:                                RESISTIVE
        TIMING_REG[9:8]:                0
TOF_0
        RAW:                                     0x0
        TIMING_REG[9:0]:                0
ERROR_FLAGS
        RAW:                                     0x0
        ERR_SIG_WEAK:                 OFF
        ERR_NO_SIG:                      OFF
        ERR_SIG_HIGH:                   OFF
TIMEOUT
        RAW:                                     0x4C
        FORCE_SHORT_TOF:         ON
        SHORT_TOF_BLANK_PERIOD: 16 x T0 -> 3.255341 us
        ECHO_TIMEOUT:                  OFF
        TOF_TIMEOUT_CTRL:         128 x T0 -> 26.042727 us
CLOCK_RATE
        RAW:                                    0x0
        CLOCKIN_DIV:                     1
        AUTOZERO_PERIOD:        64 x T0 -> 13.021363 us
TOF Control:                                Short TOF

However I can never get an echo signal. I output the signal and check it on the oscilloscope RX, LNA OUT, PGA OUT.
But in none of the points I can see a received signal.

I would appreciate any ideas or suggestions to get my circuit working.

Best regards
Daniel Pozzatti

  • 0
    TI__Mastermind 40280 points

    Daniel,

    Can you provide some details of your setup?  A picture may also be helpful.    

    How far away is your target object?  For basic testing of the received echo, I recommend placing a large, hard, flat surface about 1 or 2 feet away from the sensor.  When using a single transducer for both TX and RX, there is a dead zone at short range(usually few inches).  This is due to the ring down time of the transducer which is saturating for a short period after the TX pulses are emitted.    

    Can you share your scope shots as well?   

      

  • 0 in reply to Eddie LaCost
    Prodigy 20 points 
    Hi Eddie,Thanks for your response. 
    I'm working with a distance of 10cm. If I'm not wrong, I have TOF ~ 580us. 
    This value should be greater than my dead zone. Correct?
    This is the image of my test system at the moment:

     

    Analyzing my signals with the oscilloscope I have the following signals:

    TX and RX emission of 6 pulses and damping:
     

    TX and RX over time:
     

    TX and LNA OUT:
     

    TX and PGA OUT:

     


    Any suggestions or ideas will be welcome. 
    I've analyzed my circuit several times and I can't find anything wrong. 
    It seems to me that the circuit is filtering my signal in the 300khz band, I don't know what to think anymore. Sob

    best regards
    Daniel
     
  • 0 in reply to Daniel Pozzatti
    TI__Mastermind 40280 points

    Daniel,

    Thanks for the additional details.  

    With the expected ToF of ~580uS, you need to be using the standard ToF measurement instead of the short ToF measurement.  In your configuration below, you are using short ToF and have a timeout of ~26uS, so the receive window is missing any echo that may occur.  In the short configuration, the max timeout is 208uS, so this will not work for your setup.  Please update to standard and adjust the timeout as needed.

    10cm is also a pretty short range, so it may be close to the blind zone, but with the current timeout it would not be seen anyway.       

    TIMEOUT
            RAW:                                     0x4C
            FORCE_SHORT_TOF:         ON
            SHORT_TOF_BLANK_PERIOD: 16 x T0 -> 3.255341 us
            ECHO_TIMEOUT:                  OFF
            TOF_TIMEOUT_CTRL:         128 x T0 -> 26.042727 us
    CLOCK_RATE
            RAW:                                    0x0
            CLOCKIN_DIV:                     1
            AUTOZERO_PERIOD:        64 x T0 -> 13.021363 us
    TOF Control:                                Short TOF

    Also, we generally don't recommend the TDC1000 for air coupled applications operating lower than 1MHz.  TDC1000 is typically recommended for water coupled liquid measurements at 1MHz.  If you are able, you could consider the PGA460 or TUSS4470, which would likely provide better performance for an air coupled application.