help of design of active band reject filter

Kok you do not have the filters in cascade.

You have them both going to the summing junction of U3

Try a 60Hz notch filter and then the 800KHz low pass in CASCADE and then to U3 of gain -2 it looks like.

There are many other ways to do this.

A multiple feedback bandpass, a high pass low pass Sallen Key, state variable etc.

but they need to be in cascade ahead of U3.

Hope this helps

Dana

Kok,

I cannot see that the topology that you have shown can do what you want. Here is a possible implementation. It is a 60kHz Twin-T with a single pole at 800kHz.

Your circuit appears to have the input signal biased at 0V with the op amps powered from a single power supply. This will not perform properly. I've shown a dual power supply to bias the input within the common-mode range of the op amp. I recommend an OPA132 or OPA140 op amp. The AD op amp you have shown emits UHF radiation that will make your hair fall out.

Regards, Bruce.

thank you all for help

Bruce: do you have any reference link about the method u suggest me?

thank you

could you plz help me about the calculation ,i tried so many time but  cant get it ,its urgent

Niloo:

The venerable T-notch filter has been around since the days of vacuum tubes from which I come from.

There are very many links on the web for it's theory and design, not like the old slide rule days.

Google T-notch filter.

Many sites have Java design tools such as this one for example. 

http://sim.okawa-denshi.jp/en/TwinTCRkeisan.htm

Bruce: nice tip on the AD8671 being a UHF chatterbox.

I'll remember that.

I see by the color of your hair, same as mine, you may go back to our days when

real radios glowed in the dark ;)

Dana

Dana,

I should have broadened my observation that all op amps starting with "AD" in their part number can cause a wide range of maladies and should be avoided.  Extended use of op amps with prefix of OPA, TLC, TLV, TLE, THS will eventually cause graying of the hair but, as can be seen, no extensive hair loss.

Regards, Bruce.

Bruce:

I guess I must concur on your observations on AD.

Now that you mention it I do distantly recall taking a fancy new fangled spectrum analyzer up

into that neck of the woods with a AD part and seeing sum funny fuzz. 

Wonder what AD is doing that Burr-Brown aka TI isnt?

Not to worry about the hair.

I still got mine.

Dana

thank you very much for your help ,im not sure if im doing correct or not i set the fo=219k and get the capacitors and resistors ,im doing correct ???

:S

Mr Bruce 

im trying to find the value of your resistors and capacitors hours but i still couldnt get them ,plz help me i have to finish it by tonight 

by using the web site that dana gave me u get ur answers but by calculation on my own i cant 

im so confused by using formula for twIn T

Freq = 1/(2piR*C)
Variables: 
R1 = R2
R3 = 0.5 * R1
C1 = C2
C3 = 2 * C1

r and c are not equal but ur values are equal and the answer is vey accurate just like what i need but how can i write the calculation because i must write  down  calculation steps

Hello Kok,

In addition to all the excellent support you have been receiving regarding your active band-reject questions, I would like to add that TI has a free active filter synthesis filter tool called FilterPro, V3.1. Bruce was one of the original creators of this tool. It has been completely updated last year to include new features, filter responses and improved graphics.

V3.1 includes the provisions for bandpass and bandstop/notch filter synthesis. This tool may be of help to you. It can be downloaded off the TI website at:

http://focus.ti.com/docs/toolsw/folders/print/filterpro.html

Regards, Thomas

PA-Linear Applications Engineering