TDC1000-TDC7200EVM: Increase Gain in Rx path

Gert Mema

Part Number: TDC1000-TDC7200EVM

Hello,

I´m using the TDC7200-TDC1000EVM and changed the band-pass frequency on it. The LNA in the receive path is switched to Resistive Feedback Configuration.

When the distance between the sensor and the object gets to big, I don´t get a stop pulse, because the signal is way too small. The threshold is already switched to 35mV and the PGA Gain is 21dB.

Can I just use a resistor smaller than 900 Ohm (where C42/C43 used to be) to increase the gain? Is there another way to increase the gain?

Thank you.

over 8 years ago

0 Vishy Viswanathan over 8 years ago

TI__Mastermind 21685 points

One option is to increase the TX excitation voltage. Are you using higher excitation voltage? You can try with a smaller resistor. Please check it in capacitive mode also as we always find capacitive mode working better.

Thanks,
Vishy

0 Gert Mema over 8 years ago in reply to Vishy Viswanathan

Intellectual 305 points

Thanks Vishy.

I´m already using 200 V excitation voltage. Can you recommend a sensor with very high sensitivity? The medium is air, so the frequenycy should be about 40..50 kHz.

As I saw in the application note for TDC1000, the capacitive mode is intended for water applications.

0 Vishy Viswanathan over 8 years ago in reply to Gert Mema

TI__Mastermind 21685 points

Gert,
Not sure if you already checked this posting

e2e.ti.com/.../498792

Summarizes using TDC1000 for short distance measurement in air. Two things to note
a) we used 200kHz transducers. These transducers have more focused beam angle (7deg) and gives decent echo reflection back for TDC1000 to pick up and process. Compared to that 40-50kHz transducers have very wide beam angle (65deg or more) and there's echo from the sides and it's harder for TDC1000 to detect.
b) we used capacitive mode in the above instance.

Thanks,
Vishy

0 Gert Mema over 8 years ago in reply to Vishy Viswanathan

Intellectual 305 points

Thanks for your answer Vishy.

Actually it isn´t a short distance measurement, the distance is between 70mm and 400mm. This is the reason why we use a high voltage excitation pulse.

0 Vishy Viswanathan over 8 years ago in reply to Gert Mema

TI__Mastermind 21685 points

I guess you mean 400cm? I don't think we have tried up to 400cm in air. Assume you are using two transducers one to send and one to receive so that way you have more chance of seeing an echo. Also, try it with NUM_RX field chosen as "No Rx Even Count". That way you in the scope you get to see all the echos coming.
Thanks,
Vishy

0 Gert Mema over 8 years ago in reply to Vishy Viswanathan

Intellectual 305 points

Dear Vishy,

I actually mean 400mm (40 cm). For my application I can only use one sensor.

0 Anthony28 over 8 years ago in reply to Gert Mema

Prodigy 70 points

Hi Gert,

Sorry to revive this post but did you ever end up swapping the resistor to increase gain? If so, how did that work out for you?

Also, how did you increase your TX voltage to 200V? Did you swap components on the eval board or use an external circuit?

Thanks

0 Gert Mema over 7 years ago in reply to Anthony28

Intellectual 305 points

Hi Anthony,

I used an 900 Ohm resistor instead of C42/C43 and 200V excitation voltage, so the echo voltage is high enough. I used an external circuit which we designed at the company I work for to increase the excitation voltage.

Kind regards,
Gert

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TDC1000-TDC7200EVM: Increase Gain in Rx path