编译/ PGA460： Radar measurement results return value is not normal

i Charles,

1. Your configuration process is valid, so I have no concern here.

2. Can you share all values of the entire Ultrasonic Measurement Result command? I assume the threshold must be optimized if the values are remaining mostly unchanged.

• How did you set your threshold?  It appears that you are using the mid-code value example from the Energia example code.
• Do you have an EVM that you can use to further optimize and map the threshold?
• If you increase the number of objects to detect to 8, do any of these values change in accordance to the actual distance of an object?
• Can you also check the bit state of THR_CRC_ERR int he DEV_STAT0 register. This bit must be a value of 0 in order for the enable burst+listen command. This bit is automatically cleared if the bulk threshold command was successfully executed.
• I see you are using the DECPL pin. Are you using time or temperature decouple mode? Since the transformer is grounded through the DECPL FET, you must use time decouple mode for the transformer driver.  Note: the DECPL pin is an optional feature; you can directly ground the transformer and tuning capacitor if this feature is not needed.
• Have you confirmed that the transducer is being properly excited by probing the positive transducer terminal during burst+listen? What is the peak to peak voltage?
• What transducer part number are you using?

I suspect you are encountering a similar discussed in the PGA460 FAQ (http://www.ti.com/lit/pdf/slaa733); specifically, FAQ # 5.2 and 5.6 (linked document includes supporting images):

5.2 How can I detect more than eight objects?

Can I set the threshold to ignore ringing decay ripple or objects for a given time after bursting? How can the Threshold Offset be used? The threshold map can be set to ignore ultrasonic activity at any point of the record window, when the threshold level is set to a value of 255. The user may want to consider setting the threshold to a value of 255 during the initial burst and decay time. Even when the return data is saturated, such as during the burst window or strong return peaks, the threshold comparator will not trigger when the threshold is maximized. For threshold levels 1-8, the value of 255 can only be attained when the threshold level is maximized to a value of 248, and the threshold offset is set to a maximum positive value of +7. This offset applies to all 1- 8 levels. For levels 9-12, the offset does not apply, and these levels can be independently set to 255.

5.6 The ultrasonic measurement result data is random, very short, always the maximum value, or never updates.

Before the ultrasonic measurement results can be of any use, the thresholds must be mapped for object detection based on the echo data dump profile. Use the mid-code threshold timing and levels option to bypass the need for manual threshold optimization. The mid-code option sets the threshold to a fixed 50% detection level.

If the threshold has been set appropriately, and the value returned is always less than 10 cm, then the threshold is initially set too high, but not maximized. At low analog gains, the DSP output supplied to the data comparator to detect a threshold crossing initially ramps during the burst and decay window. As a result, the echo data dump equivalent is not immediately saturated as it is represented in the analog domain, thus the threshold comparator can be false-triggered by the initially ramped DSP output. To prevent this false-trigger, initially set the threshold to the maximum value of 255, increase your threshold deglitch time, or lower the threshold such that ramping is at an initial value above the threshold level. Alternatively, set the initial gain to a larger value such that the ramping is saturated, and does not trigger the threshold.

Best practice is to initialize the TVG and/or SR digital gain to a large value during the expecting burst and initial decay window, and radically reduce the TVG to a lower value during the later portion of the decay period to enable short range detection.

If the threshold is always at a maximum value, the threshold is set too high throughout the entire profile, or no object is detected. Reduce the threshold levels to force the threshold comparator to trigger. A forced trigger will confirm whether a burst-and-listen command has truly executed. If the ultrasonic measurement results (UMR) are not updated, ensure that the DATADUMP_EN bit of the EE_CNTRL register is disabled (default). If the DATADUMP_EN bit is enabled, the echo data dump memory is filled, and the UMR will not update because the threshold comparator disabled. Only the echo data dump memory can be filled, or the ultrasonic measurement results be captured, but not both simultaneously. When the GUI displays the echo data dump and captures the ultrasonic measurement results, two independent burst-and-listen commands are run sequentially.

You can also run a transducer echo data dump read (command 7) to visually inspect the echo data dump profile.

• Can you provide this 128 byte EDD output with the object at 30cm?

If you need to reliably detect downwards of 10cm in a mono-static configuration, then you can use high-frequency transducers in the range of 180-480kHz. See a recent E2E discussion at https://e2e.ti.com/support/sensor/ultrasonic/f/991/p/628579/2343961 which discusses a high-frequency transducer half-bridge driver implementation.

You can also use a transformer driver to excite a high-frequency transducer. If you are seeking a transducer resonating near 200kHz, I recommend the Massa 200639-501 (Model E-188/220) transducer.

You can find a full listing of high-frequency transducers and transformers at: https://e2e.ti.com/support/sensor/ultrasonic/f/991/t/620399