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TDC1000-TDC7200EVM: Sensors forum

Belkacem ABERBACHE
Prodigy 100 points

Part Number: TDC1000-TDC7200EVM

Hello,

I use TDC1000-TDC7200EVM with transducer ( Fc=300Khz – capacitance=1200pF – min resistance parrallel=150Ω) and it doesn’t work well, the goal is to use it to measure distance in the air.

Note:  (it work well with SMD15T21R111WL to measure in liquid).

 

I know that it’s necessary to change the value of some components:

I let R31= 5.36k & R34= 1k

But I changed (after read of 8.3.5 Receiver Filters & inspired by TDC1000-GASEVM):

C27=510pf

C32=400pF

C36=3000pF

C42=R=0.9K

 

Please see attached:

1°) GUI, I use CPU clock => 1.2Mhz & LNA Resistive FB,

 2°) Screenshoot obtained with C42=R=0.9K (without STOP SIGNAL)

3 & 4°) Screenshoot obtained with C42=R=0  (the STOP signal change while transducer distance doesn't change).

 attached.docx

Can you help me to understand what I need to change to have a correct signal ?

Thanks in advance,

Best regards,

Belkacem

 

 

 

  • 0
    TI__Genius 11015 points
    Belkacem,

    The TDC1000-GASEVM circuit is setup for a transducer with freq in the range 58Khz to 300khz. Many a times a transducer rated for fc 300khz will in reality have a higher value and that would not work in that circuit.

    I recommend that you use a transducer with lesser fc than 300Khz and that should work with your current circuit. Else you will have to change circuit to have a large band width.
  • 0 in reply to Bharat Aravamudhan
    Prodigy 100 points

    Bharat,

    Thank for your answer.

    In fact, I don't use TDC1000-GASEVM but TDC1000-TDC7200EVM. I change the values of components to have fc=300Khz and low-pass filter frequency at 58 Khz and high-pass filter frequency at 400Khz.

    - Can you confirm that values was good for these frequencies ?

    - Do you have a formula to calculate the right value for Cf1=C36 (between LNAOUT & PGAIN) ?

    - For frequency lower than 1Mhz, I know that I must change capacitance C42 to Resistor at 0.9K it's correct ? or R=0 ?

    - What about R30=0.2k ?

    - How can I check the right fc for my transducer (normally fc=300Khz) ? maybe I need change the low-pass filter frequency at 200 Kh high-pass filter frequency at 500Khz ?

    - I have another transducer with fc=40Khz, can you give me the right components values for this transducer ?

    Thanks in advance,

    Belkacem

  • 0 in reply to Belkacem ABERBACHE
    TI__Genius 11015 points
    Belkacem,

    The TDC1000-TDC7200EVM is intended to be used mostly with a 1Mhz frequency transducer.

    Please note that the TDC1000 has an internal LNA & PGA that gains the Rx signal and inputs that to the COMPIN pin.

    The resistor-capacitor network in TDC1000-TDC7200EVM along the LNA & PGA acts as a filter.

    Please download TINA Spice from the link: http://www.ti.com/tool/TINA-TI

    Use the modeling tool above and try to emulate a proper resistor capacitor network that suits the resonant frequency of your transistor.