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At first,i created a simple schematic of non-inverting amplifier using LM741 having a gain of 2. The supplied a.c voltage at non-inverting input is 1V having frequency of 50 Hz. And i get the result what i had expected, the output voltage of 2 v peak and 50 Hz.

In the second scenario, i kept all the parameter same expect i grounded the negative voltage supply and i get unexpected result. Peak voltage at the output is 800 mv and lower voltage is -200mv. And the screenshot of the simulated waveform is presented below.

Tx in advance. Amplifier Circuit using LM741

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    \$\begingroup\$ "... and i get unexpected result ..." - it might help if you describe what result you expected, and why. \$\endgroup\$ – Roger Rowland Jun 4 '16 at 8:12
  • \$\begingroup\$ I was expecting the same sinusoidal result as before. That's what i meant by unexpected result. Tx. \$\endgroup\$ – Abhaya Singh Pandey Jun 4 '16 at 8:15
  • \$\begingroup\$ LM741 is not a rail to rail op-amp. Check your input voltages against the supply. \$\endgroup\$ – Roger Rowland Jun 4 '16 at 8:22
  • \$\begingroup\$ I came across this curiosity while trying to get the concept of difference amplifier. Ok i will test it after i get the concept of rail to rail op-amp. One more question, can u help me to understand how the d.c voltage that is named as R4(2) in the figure (difference amplifier)acts as the offset voltage. the link for it is provided below; s33.postimg.org/km59pi2sv/test.png \$\endgroup\$ – Abhaya Singh Pandey Jun 4 '16 at 8:34
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If your input voltage swings equally positive and negative then it would be expected that your output would do the same. However, with 0 volts as your most negative supply rail this cannot happen. An op-amp can only produce output voltages within the confines of its power rails.

This won't be helped by using a rail-to-rail op-amp either.

The data sheet has the full story: -

  • Input voltage cannot be relied upon when closer than 3V to either rail (see input voltage range limits in DS)
  • Output voltage is unreliable within 3V of either rail (see output voltage swing limits in DS)

You've broken both these rules!

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  • \$\begingroup\$ I didn't get exact the line what u had written pointwise. But i got the overall story behind it. Can u plz help me out to figure the effect of the offset voltage which is labelled as R4(2) in the figure. s33.postimg.org/km59pi2sv/test.png Tx. \$\endgroup\$ – Abhaya Singh Pandey Jun 4 '16 at 17:58
  • \$\begingroup\$ Tx Digging Sedra books and datasheets i found how the d.c voltage acts as the offset voltage and how it effects the output voltage. \$\endgroup\$ – Abhaya Singh Pandey Jun 6 '16 at 9:22

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