TDC1000-GASEVM: SNAA284a, Figure 8

Arne Sieber

Part Number: TDC1000-GASEVM

Hello,

We are working on a gas flow meter with 200kHz transducers, and would like to use symmetrical excitation like described in SNAA284.

I am struggeling a bit with Figure 8, where in receive mode the transducers are connected with 2 x 10pF capacitors to GND.

R12 is 200R. The impedance of C3/C4 or C5/C6 should be much higher than R12, and when receiving, the transducers have no other connection to GND, how can that work? Would it not e required to connect the other end of the transducers to GND when in receiving mode?

Thanks, BR, Arne Sieber

over 7 years ago

0 Vishy Viswanathan over 7 years ago

TI__Mastermind 21685 points

We will come back to you on this. Thanks.

0 Arne Sieber over 7 years ago in reply to Vishy Viswanathan

Prodigy 40 points

Hello, no one from TI who can help us?

0 Vishy Viswanathan over 7 years ago in reply to Arne Sieber

TI__Mastermind 21685 points

Arne,
What is proposed there is a differential drive for the transmitting transducer. The receive transducer is still used in a single ended configuration. As explained in page 8 of the document, you can choose to implement a more elaborate switching scheme to achieve a more optimal impedance matching of the TX and RX path.
Thanks,
Vishy

0 Arne Sieber over 7 years ago in reply to Vishy Viswanathan

Prodigy 40 points

Thank you very much for your reply, even if it does not answer my question. In SNAA28a Fig 8 a switch is described to switch between transmitting AND receiving mode, where in receiving mode the receiving Piezo is connected with 2 10p capacitors to GND. We do not understand how that should work? Can you explain to us? Thanks!

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TDC1000-GASEVM: SNAA284a, Figure 8