Operational Amplifier Circuits: Inverting, Non-Inverting & More
Operational Amplifier Circuits
Non-Inverting Amplifier
The fundamental non-inverting amplifier operational amplifier configuration is shown in the figure below:
Vin = Input voltage
Vout = Output voltage
Ve = Error voltage
Vf = Feedback voltage
A = Open loop gain amplifier (specified by the manufacturer)
B = Factor of negative feedback
The output voltage (Vout) can be expressed as the error voltage multiplied by the open loop gain (A):
Inverting Summing Amplifier
The following figure shows the basic inverting summing amplifier:
Differential Amplifier
The figure below shows the basic configuration of a differential amplifier, also known as a subtractor amplifier.
Non-Inverting Summing Amplifier
Buffer
Basically, a buffer is a current amplifier that is also used as an impedance adapter.
A buffer is characterized by high input impedance, low output impedance, and a voltage gain equal to unity.
Derivative Amplifier (Bypass)
A derivative amplifier is a circuit that executes the mathematical operation called differential calculus derivation. It produces an output voltage proportional to the instantaneous variation of input voltage over time.
Common applications of a derivative amplifier are the detection of rising and falling edges of a pulse.
Integrating Amplifier
The integrator is a circuit that performs the mathematical operation called integration. The basic integrator circuit comprises a resistor and a capacitor.
Elimination of Output Offset
The circuit requires a modification previously shown to be practical because a capacitor behaves like an open circuit for continuous signals, then there is no negative feedback at frequency zero. Without negative feedback, the circuit finds any input offset voltage as a valid input voltage. The result is that the capacitor is charged and the output is saturated positive or negative, remaining there indefinitely. One way to solve this problem is to reduce the voltage gain at zero frequency by connecting a resistor in parallel with the capacitor, as shown in the figure below:
The resistance of the resistor must be at least 10 times greater than the resistance of the input. Adding a resistance of 10 R, the voltage gain in closed loop is 10 and the output offset voltage is reduced to an acceptable level successfully. When the input voltage is present.
Electrical Characteristics of Operational Amplifiers
Bandwidth
The bandwidth or BW (Band Width) shows the amplifier response to different frequencies.
Ideally, an operational amplifier must have a constant gain for all frequencies; however, in a real operational amplifier, the gain decreases as the frequency increases. This variation is due to the internal structure of the circuit and the inclusion of a frequency compensation capacitor which avoids oscillations. In the case of the LM741 integrated circuit, the capacitor is 30 pF.
The following graph shows that in open loop, the voltage gain decreases at 20 dB per decade, i.e., when the frequency increases 10 times, the gain decreases by 20 dB.