| Author |
Message |
kseng2002
Joined: 27 Aug 2004
Posts: 690
Helped: 418
Location: Malaysia
|
 27 Aug 2004 15:02 How To do the level shifting by op-apm ? |
|
|
|
|
Regarding to the subject above, i dont know the technique to shift the level of the voltage. Let say the voltage level is from -3 to 3v , but i want it to be 0 to 6v. Can anyone help me of this problem ? Thank you !
Last edited by kseng2002 on 26 Sep 2004 8:42; edited 1 time in total |
|
| Back to top |
|
 |
brmadhukar
Joined: 21 Jun 2002
Posts: 844
Helped: 29
|
| 27 Aug 2004 15:39 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
Hi,
Use the opamp as adder with a voltage follower following it. Provide a 3V supply by using a potenetial divider from the source as one of the inputs. It works well.
B R M
|
|
| Back to top |
|
|
DarkJedi
Joined: 25 May 2004
Posts: 145
Helped: 9
Location: Lima, Perú
|
| 28 Aug 2004 4:59 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
| Remember that the voltage supply for the opams must be higher than 6v, i recommend u use at least 2v more, to ensure the correct work use a power supply of 10v and -10v
|
|
| Back to top |
|
|
kseng2002
Joined: 27 Aug 2004
Posts: 690
Helped: 418
Location: Malaysia
|
| 30 Aug 2004 14:25 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
Sorry, can explain more details about how to use the op-amp as "adder" ?
I really have no idea on it ! Thx ! 
|
|
| Back to top |
|
|
djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
|
| 30 Aug 2004 15:44 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
| kseng2002 wrote: |
Sorry, can explain more details about how to use the op-amp as "adder" ?
I really have no idea on it ! Thx ! |
See the schematics: 2volts + 3volts = 5volts.
Warning: Vout must be not exceeded Vcc in this case is 12volts. V1 and V2
|
|
| Back to top |
|
|
Kevin Weddle
Joined: 10 Jul 2004
Posts: 101
Location: San Antonio, TX
|
| 30 Aug 2004 17:24 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
| Generally, you can use a capacitor to separate the DC bias. Or you can use a transistor to change the bias voltage. The difference being that you can only use a capacitor when the signal is constantly changing. That is why you should use a transistor if you want the signal to display it's voltage level rather than the DC bias when the signal stops changing.
|
|
| Back to top |
|
|
chiara
Joined: 09 Jul 2002
Posts: 49
Helped: 3
|
| 31 Aug 2004 16:58 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
Use AD8138 like device.
good luck.
|
|
| Back to top |
|
|
kseng2002
Joined: 27 Aug 2004
Posts: 690
Helped: 418
Location: Malaysia
|
| 31 Aug 2004 18:39 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
Em, now i understand how to use op-amp as "adder" ! thx for help ! But there's still 1 thing that i cant catch up ! Refer to the simple graph i draw below, that the problem that i face again... Can anyone tell me how to do that with op-amp ? Thank you ~ !
|
|
| Back to top |
|
|
Kevin Weddle
Joined: 10 Jul 2004
Posts: 101
Location: San Antonio, TX
|
| 31 Aug 2004 19:15 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
| Just bias it with a positve offset by puting the noninverting input at a greater value than the inverting. It depends how you are going to use the opamp. Generally, you will set the gain and use a voltage source to give you the voltage you desire on the inputs. It's easy to set the voltage because the opamp has that external voltage divider. Just plug in the numbers and recall that the difference between the two inputs times the gain gives you the output.
|
|
| Back to top |
|
|
kseng2002
Joined: 27 Aug 2004
Posts: 690
Helped: 418
Location: Malaysia
|
| 17 Sep 2004 12:00 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
Hi,
i can do the simulation as to shift the voltage to the positive site ,
but in real practical, i failed to do it !
Actually i'm using LM358 op-amp to do the level shifting,
i works well in the simulation but not in pratical.
Can any1 help me ?
This is urgent !
Thx for help !!!!!
|
|
| Back to top |
|
|
amraldo
Joined: 29 Aug 2004
Posts: 270
Helped: 23
Location: egypt, cairo
|
| 18 Sep 2004 1:41 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
the circuits u r using actually sums the input voltages but in the same time multiply the output by a -ve sign(note the first graph carefully) because the circuit uses a -ve feedback
to solve this problem & add another stage of -ve gain amplifier with magnitude of '1' using another opamp
|
|
| Back to top |
|
|
daojx
Joined: 20 Jul 2003
Posts: 36
|
| 19 Sep 2004 1:24 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
try work with this one
|
|
| Back to top |
|
|
savadi
Joined: 14 Sep 2004
Posts: 27
|
| 23 Sep 2004 17:31 Re: How To do the level shifting by op-apm for the ADC ? |
|
|
|
|
| You can use a differential op-amp. As you know, you can set the output common-mode voltage by common-mode feedback. Therfore If you make a buffer byop-amp and set the output common-mode voltage about 0 volt, you have a signal with 0 volt dc voltage. An important point is the stability of your op-amp. your op-amp must have phase margin larger than 67 degrees and unity bandwidth much larger than your input frequency to have enough open-loop gain to get a reasinable linearity.
|
|
| Back to top |
|
|
