Comments on: Bipolar to Unipolar Converters Based on a Summing Amplifier Configuration http://masteringelectronicsdesign.com/bipolar-to-unipolar-converter-examples/ 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/bipolar-to-unipolar-converter-examples/#comment-1124 Adrian S. Nastase Fri, 16 Jul 2010 02:06:27 +0000 http://masteringelectronicsdesign.com/?p=1044#comment-1124 khor, you're welcome and thanks for visiting. As for your question, yes, one needs to choose the op amp carefully. Op amp manufacturers show in their datasheets the gain and phase bode plots as well as the phase margin versus frequency. Typically, if you choose a unity gain stable op amp it has less chances to oscillate below unity gain. However, as manufacturers try to boost the gain as much as possible, due to competition, the op amp internal compensation may be just about right to make sure the phase margin is above 45 degrees all the way down to 0 dB gain. Below 0 dB gain, one might see an extra pole and that means trouble. Therefore, since there are many op amps out there and the designer circuit might have a capacitor that reduces the bandwidth even more, I can only advise to always check the manufacturer datasheet and the phase margin plot for that particular op amp of choice. khor, you’re welcome and thanks for visiting.

As for your question, yes, one needs to choose the op amp carefully. Op amp manufacturers show in their datasheets the gain and phase bode plots as well as the phase margin versus frequency. Typically, if you choose a unity gain stable op amp it has less chances to oscillate below unity gain. However, as manufacturers try to boost the gain as much as possible, due to competition, the op amp internal compensation may be just about right to make sure the phase margin is above 45 degrees all the way down to 0 dB gain. Below 0 dB gain, one might see an extra pole and that means trouble. Therefore, since there are many op amps out there and the designer circuit might have a capacitor that reduces the bandwidth even more, I can only advise to always check the manufacturer datasheet and the phase margin plot for that particular op amp of choice.

]]> By: khor http://masteringelectronicsdesign.com/bipolar-to-unipolar-converter-examples/#comment-1120 khor Thu, 15 Jul 2010 14:09:58 +0000 http://masteringelectronicsdesign.com/?p=1044#comment-1120 Hi, reading your previous articles on this topic I came up with pretty much the same resistors for the problem shown in figure 4. What I was wondering about is the stability of this circuit. Since the gain v_out/vin is below one, do I have to be careful when choosing the op amp? If I recall correctly there is a pretty good chance of picking the wrong op amp and ending up with an oscillator. Btw, thanks for this great site! Hi,
reading your previous articles on this topic I came up with pretty much the same resistors for the problem shown in figure 4. What I was wondering about is the stability of this circuit. Since the gain v_out/vin is below one, do I have to be careful when choosing the op amp? If I recall correctly there is a pretty good chance of picking the wrong op amp and ending up with an oscillator.
Btw, thanks for this great site!

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