Choppy output on TDC chip (max35101)

[maoterk]

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 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

[shakalnokturn]

I have no experience on the MAX35101 or on the subject in general.

Your waveform shows crossover distortion. Are you overloading the LAUNCH outputs? The datasheet doesn't say much on the subject, the only figure I noticed was 50mA...
Try using a higher resistance between LAUNCH outputs and transducer. Or at least diff. probe the voltage across them to get some idea of the current you are drawing.

If increasing the resistance enough isn't practical because of transmission losses maybe consider an external transducer drive stage.

Lowering pulse frequency could also be a compromise.

[maoterk]

Upon further investigation the issue seems to be a different one (maybe). Whenever the receiver is enabled (after the programmed delay) (Screenshot1) there is a lot of noise which makes correct comparator output impossible. As you can see in Screenshot2 the actual received signal is very clean if the receiver is enabled after the signal which is pointless. The capacitors at the receiver end are 1nF. Any ideas?
I'll try using a higher resistance between LAUNCH outputs and transducer.
thanks for the help