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Summing amp help

bungouk

Jan 10, 2012
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Could somebody help me with this one, i don't understand it. I have tried to build the circuit in multisim 11 but i'm not getting anywhere.
so if someone could take a look at the attached zip file and perhaps adjust it so at least the first part of the question works and explain what needed to be done.
I have built well i think most of the circuit but not finished as i got stuck

a – Build and test a summing amplifier with four input voltages V1, V2 , V3 & V4 using multisim . The amplifier should have a voltage gain of 1 , 2, 3 & 0.5 for V1, V2,V3 & V4 inputs


1. Set V1, V2, V3 & V4 to the following voltage levels 1, 2, 0.5 & 3. Monitor Vout with the Multimeter and verify that the voltage gain levels are set correctly.
2. Set V1 to 1KHZ at 10mVPP, V2 to 2KHZ at 20mVPP , V3 to 15 mVPP and V4 to 2V D.C. Monitor Vout with the scope and verify that the gain levels are set correctly. Explain your findings.
3. Modify your summing amplifier to convert the binary number 1101 to an equivalent analogue voltage.
 

Attachments

  • summing amp 4-input.zip
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duke37

Jan 9, 2011
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I cannot get at your zip file. What is wrong with a simple picture?

I would make a virtual earth amplifier with input resistors chosen to set the gain.
 

davenn

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Sep 5, 2009
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bungouk

hi there and welcome to the forums :)

Please upload a gif or jpg image to the forum. I personally am not even going to risk opening a zip file!!!

keep you image file to ~ 800x600 max and less than 100kb preferably less than 50kb for ease of downloading and viewing

Dave
 

bungouk

Jan 10, 2012
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Sorry please find a jpg of it
 

Attachments

  • suming amp.jpg
    suming amp.jpg
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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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25,510
The ratio of the input resistor ad the feedback resistor will give you the gain. Look at a simple inverting amplifier for the calculations.

However, note that the amplifier is inverting, so the gain will actually be -1, -2, -4, -0.5 once you get the resistors right, Will this matter? It depends on who is marking your homework.
 

bungouk

Jan 10, 2012
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Jan 10, 2012
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Thanks for the replies, I stuggling to find the resistor combinations for getting 0.5 gain. What combination should i use.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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What formula have you used to determine the gain for a given pair of resistors?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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OK, two steps:

1) rearrange the equation to show gain (Vout/Vin)

2) substitute the required gain, and Rf and calculate Rin
 
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