high frequency Op amp differentiator

Hi Sameer,

 I am so happy and thankful to you. Actually I am developing a system to measure capacitance by differentiator by applying triangular 70Mhz as input and measuring square wave out amplitude as out put. Right now I am using some built in ic for generating square wave for triangular generation ( Integration ). Is this right way to measure capacitance? Can you suggest some ideas? My requirement is that out vary from 0 to 3 voltage (square wave).

Could you suggest some single supply op amp in 70Mhz range?

Thanks,

Tharanath

Hi  Hooman,

  I am so happy and thankful for your reply. I need a single supply op amp in 70Mhz range. Would you be kind enough to suggest some op amp in this range? Also 70Mhz triangular generation technique? Should I take care about stability of differentiator? My out put is square wave amplitude( whose out put is zero to 3 v). In this 0 to 3 v span i want to measure 100 readings. So differentiator should be capable of producing accurate voltage in its ON state.

Please be kind enough to reply.

Thanks,

Tharanath 

Hi Hooman,

 I am very much excited to meet you. I am interested in writing transfer function of op amp circuit manually. Could you help me to write transfer function of your differentiator circuit ?

Thanks,

Tharanath 

Hi Hooman,

 would you be kind enough to explain practical  a differentiator in 70 Mhz range? I mean all considerations like stability and all?

Thanks,

Tharanath

Hi Tharanath,

This link might explain some of the questions you had posed as to why differentiators are inherently unstable and how to make them stable:

http://www.electronics-tutorials.ws/opamp/opamp_7.html

Regards,

Hooman

Hi Hooman,

    Thank you for your reply.I just want to measure capacitance in the range of .01nF to .71nF. So I need a differentiator circuit whose  out put varies with capacitance in the above said range. I need out varies in 0 to 3 v range according to the capacitance. Vout= Vin*RC/t  is the equation for differentiator.  

If Vin=3V, f=70Mhz, C=.71nF(Max value), then R will be around 10. When i put all those value in the circuit you sent it show noise. And one more thing is that will thecircuit work if RC>t?

Would you kind enough to help me?

Thank you,

Tharanath

Hi Hooman,

            Sincere thank you brother for replying my mail and this great effort. I am measuring soil moisture. For that 70Mhz is apt which is also used in commercial also. So is it possible to design with 70Mhz? Yesterday I set up simple RC network to measure soil moisture( soil capacitance is measured which is related to moisture). In your circuit, Using this square wave out put we can measure capacitance by the equation Vout=Vin *RC/t, BY sampling peak amplitude? Some days back I realised this differentiator using 500Khz range.

Thanks,

Tharanath

Hi Hooman, 

        When I plot bode, After initial slop, next 20db slop start at 30Mhz? and next at 1Ghz? and 0db frequency around 2Ghz.But when I calculate answer not currect. see

0db frequency=1/(2pi*10p*50)=200Mhz

last slop frequency i can see in diagram is around 1GHz. but when i calculate is 1/(2pi*50*1p) is around 3Ghz.

Thanks,

Tharanath

Hi Hooman,

   I fixed my frequency of 10Mhz. For realizing this I need triangular wave in this range. Could you help me to get this?

Thanks,

Tharanath

Hi Hooman, 

   One more help. Can you give me equation for designing component values 10 Mhz for differ. and intrgr.?

Thanks,

Tharanath

Hi,

I have the following text book which treats the differentiator and integrator extensively:

"Handbook of Operational Amplifiers Circuit Design" (author: Stout and Kaufman, McGraw-Hill Book Company ISBN 0-07-061797-X)."

Regards,

Hooman

Hi Hooman,

  My senior asked  me to design differentiator using 70Mhz. Is it possible to design differentiator in this 70Mhz with my said capacitance range(10p to 710p)?

Thanks,

Tharanath