Choppy output on TDC chip (max35101)

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maoterk

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I am trying to build an ultrasonic flow meter with the TDC max35101 and have come upon an issue. When i connect the ultrasonic transducers to the chip, the output pulses are a bit choppy (pic1) generating wrong measurements on the receiver side. It should be a smooth sinusoidal signal so that the comparator has a smooth output. When i disconnect the transducers i get the normal pulses (pic2). Why is this happening and what could i do to avoid it. The transducer's capacitance is 1200pF. The circuit is uploaded also.
thanks


 

Maybe you could tell us where you're probing. We could just guess, but that wouldn't help anyone.

Also, your "good" waveform is far from a sinusoid, why do you think it should be?
 

barry said:
Maybe you could tell us where you're probing. We could just guess, but that wouldn't help anyone.

Also, your "good" waveform is far from a sinusoid, why do you think it should be?
Click to expand...

I am probing at the transducer. The "good" output is just the pulses from the chip with the transducer disconnected. When I connect it I get somewhat of a sinusoidal signal but a bit choppy.
 

Are you sure the chip is generating transducer excitation signals with correct frequency and the launch series resistors are matching the transducer impedance?
 

The excitation signals are of the correct frequency and the series resistors are matched. I 'll rethink the power supply and see if anything is fixed.
thanks
 

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