Change inverting low pass into non-inverting with only 1 op amp SOLVED

In this question I figured out how to make a op amp filter with 1kHz lowpass and gain of 10, but it's actually -10 because its inverting:

How can I make it non-inverting +10 gain without adding another opamp? THanks

by CAMIE538
November 15, 2016

2 Answers

Answer by carrolllip86

Copy+pasted berniekorries and then moved the capacitor around and added $R_3$. You want to separate the gain and the low-pass because otherwise they mess each other up. I made them separate by putting the frequency filter on the non-inverting input side, and by putting the gain on the output / inverting input side of the circuit.

Click it, run the frequency sim, you'll see it works as promised:

ACCEPTED +2 votes
by carrolllip86
November 15, 2016

Nice. Good enough for me. Can it be done without adding another resistor?

by CAMIE538
November 15, 2016

Answer by berniekorrie

How about this?

I changed $R_2$ to $9k\Omega$ and moved it all around so the capacitor is on the output.

−2 votes
by berniekorrie
November 15, 2016

This is wrong!!! Run your simulation and you'll see. It does have gain +10 and it does start to roll off at 1kHz. BUT it also starts to flatten out at 10kHz. So probably not what you're looking for.

by carrolllip86
November 15, 2016

At "low frequencies" the capacitor C1 looks like an open circuit, so the whole thing just looks like a standard gain of +10 non-inverting amplifier. But at "high frequencies" the capacitor looks like a short circuit, which shorts out R2. Now the whole thing just looks like a gain of +1 non-inverting buffer. That's NOT how a low pass filter should act.

by carrolllip86
November 15, 2016

Good catch, my mistake.

by berniekorrie
November 15, 2016

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.