Comments on: The Transfer Function of the Non-Inverting Summing Amplifier with “N” Input Signals http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/ Electronics Design and Modeling with Emphasis on Analog Design Wed, 21 Jul 2010 05:50:16 +0000 http://wordpress.org/?v=2.9 hourly 1 By: Adrian S. Nastase http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/#comment-203 Adrian S. Nastase Fri, 04 Sep 2009 06:22:46 +0000 http://masteringelectronicsdesign.com/?p=486#comment-203 Yes, you need to match the total value of the resistors in the non-inverting input with those in the inverting input. The input bias currents will generate a voltage drop on these resistors. If the total resistor values are not equal, the voltage drop will generate an offset error, which will be multiplied by the total gain of the amplifier. For the summing amplifier with n input signals you need to make sure that R1 || R2 || … || Rn = Rf1 || Rf2. Easier said than done, but doable. At minimum, try to bring them as close as possible, or use an Op Amp with low input currents. Yes, you need to match the total value of the resistors in the non-inverting input with those in the inverting input. The input bias currents will generate a voltage drop on these resistors. If the total resistor values are not equal, the voltage drop will generate an offset error, which will be multiplied by the total gain of the amplifier.

For the summing amplifier with n input signals you need to make sure that

R1 || R2 || … || Rn = Rf1 || Rf2.

Easier said than done, but doable. At minimum, try to bring them as close as possible, or use an Op Amp with low input currents.

]]> By: Anon http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/#comment-99 Anon Wed, 19 Aug 2009 23:08:26 +0000 http://masteringelectronicsdesign.com/?p=486#comment-99 If you have n input signals in the summing amplifier, what happens with the resistive imbalance between the 2 inputs of the op amp? How do you match the input resistance for each input? And is it necessary? If you have n input signals in the summing amplifier, what happens with the resistive imbalance between the 2 inputs of the op amp? How do you match the input resistance for each input? And is it necessary?

]]> By: mattjpm http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/#comment-92 mattjpm Fri, 14 Aug 2009 22:59:39 +0000 http://masteringelectronicsdesign.com/?p=486#comment-92 Very interesting the proof of this transfer function. A summing amplifier with multiple input signals can be useful in many applications. You can create an Excel spreadsheet and plug in voltage levels and play with the resistors values until you get it right. Thanks for a job well done. Matt Very interesting the proof of this transfer function. A summing amplifier with multiple input signals can be useful in many applications. You can create an Excel spreadsheet and plug in voltage levels and play with the resistors values until you get it right.

Thanks for a job well done.

Matt

]]> By: najit http://masteringelectronicsdesign.com/the-transfer-function-of-the-summing-amplifier-with-n-input-signals/#comment-89 najit Mon, 10 Aug 2009 18:29:03 +0000 http://masteringelectronicsdesign.com/?p=486#comment-89 oh man. and fun it is. took me awhile but i finally got it. thanks for this great article. oh man. and fun it is. took me awhile but i finally got it. thanks for this great article.

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