Operational Amplifier. The Operational Amplifier (OA) in Spanish AO was the term used to name an amplifier class, it allowed to perform a series of operations such as addition, subtraction, integration and differentiation, according to the basic configuration in which said Amplifier is connected operational.
Summary
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- 1 Structure
- 2 Basic settings
- 1 Comparator
- 2 Follower
- 3 Investor
- 4 Non-investor
- 5 Inverter adder
- 6 Inverter subtraction
- 7 Ideal integrator
- 8 Ideal shunt
- 3 See also
- 4 Source
Structure
The symbol of an amplifier is the one shown in the following figure:
| Symbology | Terminals |
| V +: non-inverting input
· V-: inverter input |
The power terminals may be given different names, for example in FET-based AOs VDD and VSS respectively. For those based on BJT they are VCC and VEE. Power pins are normally omitted from electrical diagrams for clarity.
Basic settings
Comparator
This is an application without feedback. Compare between the two inputs and output one depending on which input is greater. It can be used to adapt logical levels
Follower
- It is that circuit that provides the same voltage at the output as at the input.
- It is used as a buffer , to eliminate load effects or to adapt impedances (connect a device with high impedance to another with low impedance and vice versa)
- As the voltage on the two input pins is the same: V out= V in
- Z in= 8
It has the advantage that the input impedance is very high, the output impedance is practically nil, and can be useful, for example, to be able to read the voltage of a sensor with a very low intensity that hardly affects the measurement. In fact, it is a highly recommended circuit to make voltage measurements as accurate as possible, since when measuring the sensor voltage, the current passes through both the sensor and the voltmeter and the voltage at the input of the voltmeter will depend on the relationship between the resistance of the voltmeter and the resistance of the rest of the set consisting of sensor, wiring and connections.
For example, if the internal resistance of the voltmeter is R e (amplifier input), the resistance of the wiring line is R l, and the internal resistance of the sensor is R g , then the ratio of the voltage measured by the voltmeter ( V e ) and the voltage generated by the sensor ( V g ) will be the one corresponding to this voltage divider :
For this reason, if the input resistance of the amplifier is much greater than that of the rest of the set, the voltage at the input of the amplifier will be practically the same as that generated by the sensor, and the voltage drop in the sensor and the cabling.
Furthermore, the higher the current flowing through the sensor, the greater the heating of the sensor and the rest of the circuit due to the Joule effect , which may affect the relationship between the voltage generated by the sensor and the measured magnitude.
Investor
It is called an inverter since the output signal is equal to the input signal (in shape) but with the phase inverted 180 degrees.
- The analysis of this circuit is as follows:
- V += V – = 0
- Defining currents:
and from here it clears
- For the rest of the circuits the analysis is similar.
- Z in= R in
Therefore we can control the input impedance by choosing R in .
This configuration is one of the most important, because thanks to this configuration, other configurations can be elaborated, such as the configuration of the shunt, integrator, adder. In microelectronic systems it can be used as a buffer, cascading 2.
Non-investor
As we observe, the input voltage enters through the positive pin, but since we know that the gain of the op amp is very large, the voltage at the positive pin is equal to the voltage at the negative pin, knowing the voltage at the negative pin we can Calculate the relationship between the output voltage and the input voltage using a small voltage divider.
- Z in= 8, which gives us an advantage over the inverting amplifier.
Inverter adder
- The output is inverted
- For independent resistors R 1, R 2 , … R n
- The expression is greatly simplified if resistors of the same value are used
- Input impedances: Z n= R n
Inverter subtractor
- For independent resistors R 1, R 2 , R 3 , R 4 :
- As before, this expression can be simplified with equal resistances
- The differential impedance between two inputs is Z in= R 1 + R 2
- It should be noted that this type of configuration has a low input resistancecompared to other types of subtractors such as the instrumentation amplifier .
Ideal integrator
- Integrates and inverts the signal (V inand V out are time dependent functions)
-
- InitialV is the output voltage at the time source
Note: The integrator is not used discreetly in practice since any small DC signal at the input can be accumulated in the capacitor until it is completely saturated; not to mention the offset characteristic of the same operational, which is also accumulated. This circuit is used in combination in feedback systems that are models based on state variables (values that define the current state of the system) where the integrator maintains a state variable in the voltage of its capacitor.
