TDC1000: TDC1000 no stop signal

JJ Martin

Part Number: TDC1000
Other Parts Discussed in Thread: TDC7200

I set the Vthld to -75mV and use the combination of TDC1000&TDC7200 to sensing the ultrasonic wave.

As I know when the compin signal passes through VCOM and Vthld , there will generate some stop pulses.

Here is my question .....
There is sometimes no stop pulse generated when the COMIPN signal is obviously down below Vthld .

For what reason may cause the phenomenon ?

CH2 = COMPIN signal
CH3 = STOP pulse
CH4 = VCOM level

Normal situation

Unnormal situation

over 5 years ago

0 Bharat Aravamudhan over 5 years ago

TI__Genius 11015 points

Martin,

The COMPIN pin crossing is too small for the device to consider it for STOP pin generation.

0 JJ Martin over 5 years ago in reply to Bharat Aravamudhan

Prodigy 130 points

Hi , Bharat,

thank you for your reply ~

But I hava another image shows that the compin signal just attached Vthld could also generate a stop pulse.

Is that normal?

Or that would have a stop pulse or not occasionally whenever COMPIN signal is too close to Vthld(-75mV) ?
CH4(green) = STOP
CH2(blue) = COMPIN

And how far the COMPIN signal below Vthld (according to past experience) guarantees generating stop pulses?

0 Bharat Aravamudhan over 5 years ago in reply to JJ Martin

TI__Genius 11015 points

JJ Martin,

There is no specific levels until which the THLD can be placed such that it will pick out all the pulses, since no matter what the THLD there could be some small signal which could be missed. I suggest that you setup the THLD such that you get a repeatable correct Time of Flight.

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TDC1000: TDC1000 no stop signal