Capacitor value of LC Tank

Edgard

Intellectual 610 points

Other Parts Discussed in Thread: LDC1000EVM

Dear all,

I have a question about LC tank.

I designed "Original Coil (like Air coil)", then I have evaluated the performance many times with LCR meter.

I have to set LC frequency 200kHz, but Coil inductance value is very large, 50mH.

I'm worrying about the capacitor value very small, it is 12pF at 200kHz.

According to Datasheet, LC frequency is defined from 5kHz to 5MHz. So if LC frequency is satisfied with this range, even though capacitor value very small, the capacitor value is no problem?

Thanks at advance and kindest regards,

Edgard

over 11 years ago

0 Ben Kasemsadeh over 11 years ago

TI__Genius 13650 points

Hello Edgard,

I recommend using an LC tank with a larger capacitor value. With a 12pF capacitor, any trace/wire parasitic capacitance can affect the oscillation frequency and may affect the measurement accuracy.

0 Edgard over 11 years ago in reply to Ben Kasemsadeh

Intellectual 610 points

Dear Ben Kasemsadeh,

thanks a lot! Your response very quick! Amazed.

Okay, I can understand. I'll try to change large capacitor. And I'll redesign coil.

Thank you again.

Kindest Regards,

Edgard

0 Ben Kasemsadeh over 11 years ago in reply to Edgard

TI__Genius 13650 points

Hello Edgard,

you're welcome, I'm glad I could help.
Yes, decreasing inductance and using a larger capacitor would probably be best for your design.

0 Edgard over 11 years ago in reply to Ben Kasemsadeh

Intellectual 610 points

Dar Ben Kasemsadeh,

thanks again.

To tell the truth, on my system, host MCU read Rp directry, through LDC1000 registor.

Target object is very small, then I had to increase inductance value of original coil.

But on GUI (LDC1000EVM ver1.0.3.0), inductance is more stable than Rp,

and L is changing dramatically when ldc1000 detected the target.

I can begin to redesign.

Kindest Regards,

Edgard

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Capacitor value of LC Tank