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What is the difference between single and dual supply opamp?

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leohart

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Both have no ground pin but only V+ and V- supply pin while The single supply opamp: v+ -> VDD,v- -> GND. Dual supply opamp: v+ -> VDD v- ->VSS. But how does the opamp know this difference in supply configuration? I think every opamp can be used as single or dual supply depend only on how you connect V+ and V- supply pin, So why we still diff single/dual supply opamps?
Anyone knows why?PLS give your comments,thx!

ps:In razavi,he always connect a ckt to vdd in the upper,and to gnd in the bottom. Gray connect always to vdd and vss. Some other books have both configurations.But it seems bjt always use vdd and vss, but cmos can use both vdd and gnd or vdd and vss.
Is there any difference here?Can I use vdd/gnd and vdd/vss interchangably in all this ckts?
 

Using dual supplies will allow the output to swing both - and +, almost rail to rail. If the - rail is connected to gnd with a single supply the output will swing from just above 0 to just below + rail. Which you use depends on the application. If you a just amplifying from a circuit with a common ground, then single supply is ok. Or say you want to amplify a sine wave with a centre zero reference, then you must use a dual supply. Doing a search on the net for op amp theory will give you a better understanding.
 

    leohart

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Re: What is the difference between single and dual supply op

GrandAlf said:
Using dual supplies will allow the output to swing both - and +, almost rail to rail. If the - rail is connected to gnd with a single supply the output will swing from just above 0 to just below + rail. Which you use depends on the application. If you a just amplifying from a circuit with a common ground, then single supply is ok. Or say you want to amplify a sine wave with a centre zero reference, then you must use a dual supply. Doing a search on the net for op amp theory will give you a better understanding.

Then why do some opamps' datasheets say:"...xxx opamp capable of single supply operation"? It seems single supply operation is one of its highlights which distinguish it from opamps can only work with dual supplies(are there any?)

For the most classic 741,can it work with single supply?

Also,for a +5V single supply opamp to swing most effectively, the input signal should referenced at 2.5V dc point,right?but if I configure the feedback as noninverting with 2(for single ended amplification),then the dc reference point will become 5V.the same problem doesnt exist in dual supplies because the signal are referenced at gnd there.How can I solve this problem?
 

Re: What is the difference between single and dual supply op

I remember some opamp schematics from the 80's which have a +5V/GND/-5V supply connections but use the full range +5V/-5V for the input stage and the output stage. Not exact the hole range because of the limitation of devices regarding input common mode range or output device saturation voltage. But the GND is used in these opamps to supply some internal bias circuit. I think later they have rejected the GND connection and you can connect with VDD and VSS only.
 

from the 741 era, the opamp can work without gnd pin.but without gnd pin,what's the difference between vdd/vss supply and vdd+vss/gnd supply,the opamp wouldnt know it is two polar supply or single polar
right?
 

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