high pass filter with a summing amplifier

spanika kamuni

Other Parts Discussed in Thread: THS3001, OPA695, THS3201, THS3091

Hello,

I want to make a non inverting summing amplifier as a high pass filter whose Fc = 10M, how would the schematic look like...

I found converting a single ended filter to a FDA filter but I couldnot find any ideas of making a filter if 2 Inputs are on same end.

I am using THS3001 op amp.

over 9 years ago

0 Samir Cherian over 9 years ago

TI__Genius 12631 points

SummingAmp.TSCHere is one method. You can also just have a summing-amplifier followed by a passive high-pass filter.

0 spanika kamuni over 9 years ago in reply to Samir Cherian

Intellectual 370 points

hello Samir,
can you please explain who to adjust the gain to 0 db

if I use the same to make a low pass filterLowpass.TSCwhy is the gain differing.

and more over, suppose if I give 5 v at Input, my circuit no longer behaves as summer.

i an not getting 10V at Output.

It works good with the schematic you sent but not with the one I have drawn.

high pass.TSC

0 Samir Cherian over 9 years ago in reply to spanika kamuni

TI__Genius 12631 points

For 0dB gain configure the amplifier as a unity gain buffer. In the case of the THS3001 you are using a current feedback amplifier which depends on feedback resistance for stability. From the datasheet for G=1 (Page 4, BW section), the value of the feedback resistor is 1kOhm.

Your LPF circuit did not have any power supplies.

Your HPF circuit did not have any power supplies.

0 spanika kamuni over 9 years ago in reply to Samir Cherian

Intellectual 370 points

hello Samir,

sorry for the meaningless questions I asked.

I realised that I missed power supply only after I left my work place yesterday.

How can I make this a higher order filter meaning 2nd or 3rd order so that my curves are flat.

i understand making a 2nd, 3rd oder filters using single opamp. but using adder I am getting confused where to add my R's and C's so that I can make it a higher order filter.

0 Samir Cherian over 9 years ago in reply to spanika kamuni

TI__Genius 12631 points

I am not sure how to do make it a higher order filter and use it as a summer. I think its best to complete the summing operation using a 1st order filter and add a 2nd stage, higher order filter.

0 spanika kamuni over 9 years ago in reply to Samir Cherian

Intellectual 370 points

Hello Samir,

As you have suggested I am trying to add filters in next stage.My low pass Looks good. but for high pass I see some oscillations. §rdOrderAdder.TSCis there a way to eliminate it

0 Samir Cherian over 9 years ago in reply to spanika kamuni

TI__Genius 12631 points

Hello,

Couple of things:

1. The THS3201 is currently NRND (not recommended for new designs) so please refrain from using this in your circuit. You can either use the THS3001, OPA695 or THS3091 as alternate amplifiers depending on the power supply and bandwidth needs.

2. It looks like the problem in the circuit is the inability of the U4 stage to drive the capacitive load on the subsequent stage. The LPF has a series resistor to isolate the capacitance. Please see the attached circuit where I have added a series resistor of R10=40Ohms to isolate the capacitance. I also changed the value of R13 and R14 from 680ohm to 750ohm to get a little bit of extra phase margin. The simulations look good now.

-Samir

Adder.TSC

0 spanika kamuni over 9 years ago in reply to Samir Cherian

Intellectual 370 points

Thankyou Samir,

I changed THS3201 to THS3001, everything Looks good

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high pass filter with a summing amplifier