TLV3601EVM: output signal of comparator is attenuated which is not able to recognize by TDC

Satya

Part Number: TLV3601EVM
Other Parts Discussed in Thread: TLV3601, TDC7201

We are using TLV3601/03 EVM for ToF measurement.

Detector output signal connected to Non inverting terminal and a ref voltage at inverting terminal of TLV3601.The out of TLV3601 is connected to TDC circuit as Stop pulse.

Issue - TLV3601 output signal (around 2V ) is highly attenuated (around 100 mV) while connecting to STOP pin of TDC and TDC is not consider it at transition pulse for time measurement.

Further few more clarifying questions:

TLV3601/3 EVM board have few zero ohm resistors as per EVM Schematic. Which are to be populated in case of TLV3601DCK comparator IC.
Any care to be taken with regard to reference voltage for TLV3601

Thanks

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 311870 points

What are the characteristics of the load? Are you using a 50 Ω cable?

0 Chi Nguyen1 over 1 year ago in reply to Clemens Ladisch

TI__Genius 11701 points

Hi Satya,

Additionally, how exactly do you have the EVM configured and how are you taking your measurements? Do you have it set up as shown in the EVM users guide?

www.ti.com/.../snou183.pdf

0 Satya over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

I have followed TLV3601 EVM user guide, the output of comparator is available at SMA connector through 1K ohm resistor (attenuation) which is further connected to TDC input (terminated with 49.9 ohm resistor) on TDC7201 EVM board through 50 ohm coaxial cable.

0 Satya over 1 year ago in reply to Chi Nguyen1

Prodigy 10 points

Following the EVM reference guide, The EVM is powered with +3V supply, There are few 0 ohm resisters (R1 to R6), out of which R5 and R6 are unpopulated in our case and attenuation resistor R8 value is 1 K ohm. We are measuring signal at oscilloscope.

0 Clemens Ladisch over 1 year ago in reply to Satya

Guru 311870 points

The 1 kΩ and 50 Ω resistors form a voltage divider, so the attenuation from 2 V to 0.1 V is to be expected.

This particular configuration is optimized for a 50 Ω-terminated oscilloscope (which is able to sense smaller voltages). In a real application, you would place the TDC near the comparator and use an unterminated line into a high-impedance input.

Do not use J5 but J10, and use a plain cable that is as short as possible, without termination. The typical output impedance of the TLV3601 is 60 Ω, so you should use 0 Ω or some small value for R8. (Check with an oscilloscope whether you get ringing at the TDC input.)

0 Satya over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

" In a real application, you would place the TDC near the comparator and use an unterminated line into a high-impedance input." if I got correctly, you mean the 49.9 ohm terminating resistors connected on TDC input lines to be removed from TDC EVM board.

0 Clemens Ladisch over 1 year ago in reply to Satya

Guru 311870 points

Yes.

0 Chi Nguyen1 over 1 year ago in reply to Clemens Ladisch

TI__Genius 11701 points

Sorry for the confusion Satya. Clemens has summarized the changes needed quite well. Hope this helps with the issue you are seeing.

0 Satya over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Thanks Clemens.

This worked and TDC able to make measurements.

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TLV3601EVM: output signal of comparator is attenuated which is not able to recognize by TDC