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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 |
November 15, 2016 |
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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: |
by carrolllip86 November 15, 2016 |
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Nice. Good enough for me. Can it be done without adding another resistor? |
November 15, 2016 |
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How about this? I changed $R_2$ to $9k\Omega$ and moved it all around so the capacitor is on the output. |
by berniekorrie November 15, 2016 |
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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. |
November 15, 2016 |
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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. |
November 15, 2016 |
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Good catch, my mistake. |
November 15, 2016 |
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