I am trying make an amplifier with UA741 to amplify signal from ultrasonic sensor. I tested this circuit with a sinusoidal signal from function generator but this only raised the signal level adding DC component nearly equal to voltage applied in the pin 7 (marked +9v).

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Am I missing something obvious here enter image description here

Any better solution to amplification are also welcome.

  • 3
    \$\begingroup\$ what circuit? Where's your schematic? \$\endgroup\$ – Brian Drummond Aug 3 '15 at 10:37
  • \$\begingroup\$ Blindly, I assume that you are using single supply only, correct? \$\endgroup\$ – LvW Aug 3 '15 at 10:53

You are grossly misusing your op amp. If you haven't done so already, look at the data sheet and pay attention to Figure 5. Note that at 40 kHz with a +/- 15 volt supply you might hope for +/- 3 volts out, but notice that this is way out on the end of the operating range. Your circuit only uses a single 9 volt supply, so there is simply no reason to think that your 741 will operate successfully.

The answer to your problem is simple: get a different op amp. It needs to be specified for operation at 9 volt supply, and it must be specified for operation at at least 40 kHz.

  • \$\begingroup\$ Note Figure 7 as well. The open-loop gain of the '741 at 40 kHz is only about 26 dB, which is a voltage ratio of about 20. Figure 5 is related to the slew-rate limitations of the chip's output stage. \$\endgroup\$ – Dave Tweed Aug 3 '15 at 11:18

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