what is the advantage and disadvantage of both mode?can we use single supply opamp everywhere or dual supply opamp everywhere?
Single Supply Opamp has only one supply rail (+VCC) to an opamp for which your applied signal will be amplified or swing only in between the +VCC and GND.Therefore, your output voltage has a swing in between +VCC and GND rails.
Dual Supply opamp has two supply rails with reference to GND to an opamp i.e +VCC and -VCC rails.Your applied voltage can swing between these two voltage levels.Hence, the output signal can swing only between these voltage(+VCC and -VCC) limits and they cannot exceed above these levels.
For example, in an audio signal amplification, the input audio signal(Voice) can swing between +ve and -ve voltage levels(usually in mV). So this input signal can be amplified to +12V(+VCC) and -12V(-VCC) if your apply the +VCC=12V and -VCC=-12V.
Please add your values to this statements....
opamps often need to have inputs a little less than +ve supply and a little more than -ve supply. In 741, when used with +/- 15V, the input should be between 13V and -13V. It is a dual supply op amp. In some op amps, the input can be as close to negative as a few mV. LM358 is an example of that. you may call it a single supply op amp, as it can be operated from 0 to 12V and can accept inputs down to zero volts. but the output cannot be expected to be zero for a unity gain followrer with zero input. however it performs well so far as you expect an output of say 100mv to 10v. Often one prefers to bias this single supply op amp at half the supply voltage. So with 0 to 12V applied, you may tie the positive input at 6V, and connect a signal through a capacitor to an inverting amplifier, say with ri of 10k and rf of 100k.. the output will have a quiscent value of about 6V but can swing from 100mV to 10V. You may also use the 741 in the same form. But output can only swing from 2V to 10v and not 100mV to 10V. there are rail to rail I/O amplifiers where input can get close to negative supply or positive supply and output can almost swing from 100mV to 11.9V when used with 12V supply. But remember that output is one sided, and you cannot expect negative outputs. Use circuit maker (student version) to simulate these circuits at zero cost. Today 5V operated op amps are very popular. But they can swing from 100mv to 4.9V.So ensure that you expect this to be the range of output, be it inverting or noninverting amplifier. If used asinverting schmitt trigger, keep positive input at say 1v and enusre that input to negative is say 1V +/- a few mV. Always use circuitmaker to verify your existing or nonexisting knowledge.
Some very good comments above.
To me the main advantage of single-supply opamps was always the reduced power circuitry. However, I have found that in practice a simple charge-pump inverter such as the ADM8829 (99% efficiency, small, 25 mA output, etc.) provides a satisfactory negative rail suitable for most applications and consequently the benefits of the greater availablity (at present) of high-performance double-supply opamps become difficult to ignore.
Now I always select the opamp first (based on parameters) and worry about the single- or double-supply power requirements later.
There is a useful guide for single-supply designs from TI:
http://www.ti.com/lit/ml/sloa076/sloa076.pdf
Maxim document on design trade-offs between single- and double-supply opamps:
http://www.maximintegrated.com/en/app-notes/index.mvp/id/656
ADM8829 charge pump inverter:
http://www.analog.com/media/en/technical-documentation/data-sheets/ADM8828_8829.pdf
Basically it is... the supply. The internal circuitry of a dual supply OPAMP and the one of a single supply are identical.The difference is again in the biasing circuit.
The high impedance inputs can be correctly biased with some very simple network and therefore don't need a special capability of the supply circuit. For example a simple inverting amplifier can work with respect to a certain "central" voltage, connected to the positive input. This voltage, can be called "ground" and can be provided by a resistive voltage divider connected to V+ and V-. The big difference is in the low impedance output. If this output is DC connected to the load, there must be a supply terminal able to source or sink the output current, therefore a supply circuit able to do that is needed. In the inverting amplifier example, if the load is DC coupled, you want that when the input is set to ground no current flows in the load and this can not be obtained connecting the terminals of the load either to V+ or V-, you need a third terminal that is set in between V+ and V- and is able to sink current when the output is positive and to source current when the output is negative.
The only difference between single- and dual- supply opamp is that in single-supply opamps one of the supply rails corresponds to the signal reference voltage, while in dual-supply opamps the reference voltage needs to be a third, independent voltage, which is usually located at one-half the swing from the positive to the negative supply. Considering that a conventional opamp is a differential-input, single-ended output circuit, the signal reference voltage is in practice the reference with respect to which the output voltage and the common-mode input voltage are defined.
Considering that the definition of a "reference voltage" can be regarded as something rather arbitrary to a certain extent, it maybe wondered if there is a difference in hardware between single- and dual- supply opamps. As a matter of fact, opamps which require a dual supply voltage are circuits in which the output swing and the common-mode input swing do not include any of the two supplies. As such, if operated from a single supply (connecting the other to the reference), such circuits will not be suitable to deliver a "zero" output and/or to process an input with a "zero" common-mode but their useful swing will be limited to a some not well defined voltage above the reference. And this could be disturbing for analog signal processing.
On the other hand, using a single-supply opamp with a dual supply is always possible and is just a matter of conventions: in a single-supply opamp, in fact, if the supply terminal is tied to a conventionally positive supply +Vdd/2, the reference terminal is tied to a conventionally negative supply -Vdd/2, and signals are referenced with to the "zero" of the two supplies, everything works fine and the swing of the output will surely reach one of the rails.
In conclusion, practical circuits which can be found in commerce as "single-supply opamps" are less limited and more flexible than those indicated as "dual-supply" opamps.
True that zero is a voltage. But dual supply means a voltage other than zero being applied to supply rails, I guess. I have often found statements such as " when no input is connected "... the user has to identify whether he kept the input pin open or shorted to ground. Non inverting amplifiers can give you a lot of head ache if input is kept open.
Zero voltage every means the pin shorted to ground (zero output resistance of the voltage source). If the input is open - it means zero current (infinite output resistance of the current source).
And any input of real OPA needs some DC input current to work right. It is known matter.
Good answers, but they address how a ss opamp is used, not what it is.
The two defining characteristics of a single supply opamp are:
1. The input range extends to the negative supply voltage or below.
2. The output range extends to near the negative supply voltage.
A good example is the LM358.
Single supply op amps can be used in dual supply systems without any problems.
Dual supply op amps can be used in single supply systems with some caveats. The supply voltage must be high enough to insure that there is adequate input and output range. Also, the working range will tend to be in the middle of the supply range, which may be inconvenient.
I’ll assume that by single supply op-amp you mean a rail-to-rail type. As John said, most op-amps can be used with single or split (bipolar) power supplies, but for a particular application it all depends on the size of the voltage supplies available. It also depends on the technology used for fabrication of the op-amp. As many are aware, most modern high-speed op-amps have much lower specified maximum supply voltages due to the reduced breakdown voltages of the internal devices.
When using low-voltage supplies (below 5 V), typical with low-power battery operated applications, then rail-to rail inputs or outputs are often required to maximize headroom. Usually a rail-to-rail output op-amp will have an input that can extend below one of the supply rails (usually the negative), and a rail-to-rail input and output op-amp has an input that can extend beyond both supply rails. A rail-to-rail output stage can get NEAR to the rails, depending on how much current is being supplied at the output.
The disadvantage of a non RR op-amp at low supply voltages is pretty obvious. If we were to run the old workhorse, the uA741, off a single 5V rail then we’d have about 1 V of common-mode input range, and about 3V of output range (if the datasheet is to be trusted). With a RR type the input and output swing is much greater.
The disadvantages to a RR type amplifier is a bit less obvious. As I said earlier, the input can usually get to at least one supply rail. For an inverting type circuit, where the inputs are fixed at a near DC level, then this is usually not a problem. Nor is it an issue with a non-inverting arrangement where there is some gain (in excess of two maybe) as the common-mode input range will not be required to span the entire supply range. However, for applications where the entire supply range is required, such as a unity gain buffer, a RR input stage is required, which usually features an architecture that switches between two paralleled differential amplifiers when a certain input level is reach. This can add to non-linearity, and would most likely limit the maximum speed of the amplifier.
As for a RR output stage, they rely on the saturation voltage of two common-emitter, or common-source, connected transistors, and therefore will place constraints on the speed of the output if it comes close to either rail, since the output transistors will transition between two regions of operation, slowing the response time of the output. The saturation voltage will also increase with an increase in load current, therefore reducing how far near either rail the output can reach.
Your comment on use of 741 with 5V RR
is a good and practical observation that I have seen violated
... with "mysterious" results.
Glad to meet an engineer who reads / trusts the data sheet.
...
Once, 1979, I did a little project wherein I stacked ten LM741 ,
soldered leg-to-leg as an audio amp demo for class-lab.
...
I expected no magic, only the mysteries that come with not paying attention to the Data Sheet.
Results : increased input currents, internal capacitance interacting, and decreased f(max) and decreased Gain(max) ... but increased Power Out . It was a "fun" thing to do and show the students.
As I recall, I used +/- 12V power, and had a controllable gain of about 10. More attempted Rf/Ri gain led to oscillating tendencies on the proto-boards. Increased Pout was available.
...
Obviously not a engineer level project. The students could experience what happens when the data sheet is not read first.
Josef,
It is interesting to clarify the reason why "Zero voltage every means the pin shorted to ground (zero output resistance of the voltage source)"...
Cyril,
Since we are temp off the Single/Dual Supply subject,
and on to experimental use of data sheet design cautions :
my data sheets for the LM741 and LM318 and LM308
have always provided good framework for designs.
However ...
In the early 80's I had a project to design/fabricate a set of Instrumentation Amps (iAmp) to pull in myographic ( muscle cell ) signals from Cerebral-Palsy patients. First run device was also receiving A.M. radio signals from three nearby commercial 'music' stations. I could tune one-of-three by changing the "ground" connection of the main power supply from the properly grounded "ECG" green wire , to the properly grounded conduit at various points. I devised a method to generate a driven ground reference for the set of three iAmp . ( I now realize that there is a 'standard practice' and circuitry to do this. ) As I recall, I used a triad of LM308 (hi beta bipolar opAmp) to build each iAmp group. As I recall, I used the equipotential ground to which the #3 LM308 was attached, and ran this through a #4 LM308 to literally drive the ground reference for the #1 iamp and #2 iamp . I even measured the length of the wires to the equipotential ground point.
... Something like that, as an old apprentice recalls.
... So, the interferring signal was still present but drastically reduced.
Then came the surprise cure ... a Faraday Shielded Room.
All of the above were required in addition to the Data Sheet !
Glen Ellis ( www.GeoCities.WS/glene77is )
I've only used opamps in instrumentation and analogue computing applications, employing differentiators, integrators and the like. In such applications, everything is DC-coupled, so having an opamp sitting with 6 volts on its ouptut pin under quiescent conditions could be an embarrassment for circuitry like A/D converters following it. Everything ran off two rails, so that outputs could sit in between them i.e at zero volts.
Dear Mr. Biswajit Singh
Operation of op amps from single supply voltages is useful when negative supply voltages are not available in practical circuits.
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