SLAA941 March   2020 TUSS4440 , TUSS4470

 

  1.   TUSS44x0 Software Development Guide
    1.     Trademarks
    2. 1 Introduction to High-Level Software Flow
    3. 2 Main Energia Sketch File
      1. 2.1 MCU Initialization
      2. 2.2 TUSS44x0 Configuration
        1. 2.2.1 TUSS44x0 Odd Parity Calculation
        2. 2.2.2 TUSS44x0 Settings
          1. 2.2.2.1 Driver Settings
          2. 2.2.2.2 Receiver Settings
      3. 2.3 Read Ultrasonic Time-of-Flight
        1. 2.3.1 Run Time-of-Flight
        2. 2.3.2 Post-Process Data
        3. 2.3.3 Convert Time-of-Flight to Distance
    4. 3 Energia Examples
      1. 3.1 GetDistance.ino - COM Terminal Input Example
      2. 3.2 VOUT_ADC_Capture.ino - Standalone Example
    5. 4 References

2.2.2.2 Receiver Settings

The TUSS44x0 band-pass filter center frequency in the BPF_HPF_FREQ bit field must be set to equal the center frequency of the transducer. For more information, see the Bandpass Filter Center Frequency Configuration table in the TUSS4470 Direct Drive Ultrasonic Sensor IC With Logarithmic Amplifier Data Sheet. This value is centered to 40.64 kHz by default. The band-pass filter mode is only compatible up to 500 kHz. For transducers with a center frequency above 500 kHz and up to 1 MHz, use the high-pass filter mode by settings the BPF_BYPASS bit field to 1h to bypass the band-pass filter. Once in high-pass filter mode, set the value of BPF_HPF_FREQ to 1Fh for a high pass filter corner frequency of 400 kHz.

The logarithmic amplifier has two controls: slope and intercept. These settings will change how the log amp output responds as a function of input amplitude. In general, as the log amp slope increases, the log amp output gain increases, and as the log amp intercept decreases, the log amp output gain increases. By default, the log amp settings are set to nominal values. To override the nominal settings, set the LOGAMP_FRC bit field to 1h to enable the use of the LOGAMP_SLOPE_ADJ and LOGAMP_INT_ADJ bit fields. For more details on the log amp, see the Logarithmic Amplifier for Ultrasonic Sensor Signal Conditioning. The low-noise amplifier has a fixed gain, and can be set by the LNA_GAIN bit-field.

The TUSS44x0 is an analog front-end device, meaning the output is analog signal that has been pre amplified and filtered. More specifically, the TUSS44x0 output at the VOUT pin has been amplified by a low-noise amplifier, band-pass or high-pass filtered, and logarithmically amplified before becoming available as a demodulated signal to an external system. The VOUT signal can be captured by an ADC for additional post-processing by an MCU. The VOUT output can be scaled to a 3.3 V or 5.0 V referenced ADC by setting the VOUT_SCALE_SEL bit field to 0h or 1h, respectively.

The TUSS44x0 includes a built-in echo interrupt and zero-crossing intelligence in the event the VOUT signal can not be captured or does not need to be captured. The echo interrupt signal is available on the OUT4 pin that goes high when the signal on the VOUT pin crosses a threshold as defined by the ECHO_INT_THR_SEL bit field. This function is disabled at device power up, but can be enabled by setting the ECHO_INT_CMP_EN bit field. As long as the VOUT signal is higher than this threshold, the echo interrupt signal is held high. The signal goes low asynchronously when the VOUT signal drops below the programmed threshold. This signal can be used to interrupt a MCU when an object has been detected. The threshold value is also dependent on the setting of the VOUT_SCALE_SEL bit field. This echo interrupt features removes the need for an ADC if the post-processing is intended to perform the same function to determine the time-of-flight.

A zero-crossing signal is output at the OUT3 pin, which can be used to validate the frequency of the received echo signal to provide robustness against interference from other signals. This zero-crossing signal is derived from the raw amplified input signal from a particular stage as it is being demodulated in the log amp block. This function is disabled at device power up, but can be enabled by setting the ZC_CMP_EN bit field. When enabled, the ZC_CMP_STG_SEL bit field is used to select which log amp gain stage is used to generate the zero crossing signal while the ZC_CMP_HYST bits control the hysteresis of the zero-crossing comparator. The stage selection to see the OUT3 pin toggling depends on the strength of signal received by the log amp and has to be configured depending on the application. For large amplitude of input signal, a lower stage of the log amp should be selected. For lower amplitude of input signal, a higher stage should be selected. To avoid switching noise generated by the toggling of the zero-crossing comparato,r when the ZC_EN_ECHO_INT bit is set, the zero-crossing output will only be enabled while the echo interrupt signal is high.