Operational Amplifier Circuits - General

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					Operational Amplifier Circuits - General
Operational Amplifier (op-amp) circuits are linear active circuit devices. The prime
function of the op-amp circuit is signal amplification. Op-amp circuits are used a wide
range of circuits for instrumentation, control applications, and communication. The op-
amp circuit consists of the operational amplifier, external circuitry, input signal source or
sources, and DC voltage supplies. The operational amplifier is a five-terminal device
with a noninverting (+ sign) terminal, an inverting terminal (- sign), an output terminal
(Vout), a positive power supply terminal, +Vcc, and a negative power supply terminal,
-Vcc. The circuit’s signal amplification or gain is described as the ratio of the output
voltage to input voltage, K = Vout/Vin. The output voltage is Vout = K x Vin.

Inverting op-amp
The following schematic displays an Inverting Operational Amplifier circuit. The function
of the Inverting op-amp circuit is to produce an inverted and amplified version of the
input signal, signal inversion. This is Vout. The circuit’s key features are that the input
and feedback signals are both applied to the inverting terminal and the noninverting
terminal is connected to ground. The inverting circuit gain is K = -R2/R1.


Noninverting op-amp
The following schematic displays a Noninverting Operational Amplifier circuit. The
function of the Noninverting op-amp circuit is to produce an amplified version of the input
signal, no signal inversion. This is Vout. The circuit’s key features are that the input
signal is applied to the noninverting terminal and a voltage divider provides a feedback
path from the output to the inverting terminal. The noninverting circuit gain is
K = 1 + R1/R2.

Summing op-amp
The following schematic displays a Summing Operational Amplifier circuit. The function
of the Summing op-amp circuit is to produce the inverted sum of two amplified input
signal sources. This is Vout. The circuit’s key features are that the two input and
feedback signals are applied to the inverting terminal and the noninverting terminal is
connected to ground. The output voltage is Vout = -(Rf/R1 x V1 + Rf/R2 x V2).

Integrating op-amp
The following schematic displays an Integrating Operational Amplifier circuit. The
function of the Integrating op-amp circuit is to produce the integrated version of the input
signal. The circuit’s key features are that the input and feedback signals are applied to
the inverting terminal and the noninverting terminal is connected to ground. Also, a
capacitor is used in the feedback path rather than a resistor.

Differentiating op-amp
The following schematic displays a Differentiating Operational Amplifier circuit. The
function of the Differentiating op-amp circuit is to produce a differentiated version of the
input signal. The circuit’s key features are that the input and feedback signals are
applied to the inverting terminal and the noninverting terminal is connected to ground.
Also, a capacitor is used in the input path rather than a resistor.

Subtractor op-amp
The following schematic displays a Subtractor Operational Amplifier circuit. The function
of the Subtractor op-amp circuit is to produce the difference between two amplified input
signal sources. This is Vout. The circuit’s key features are that one input signal and the
feedback signal are applied to the inverting terminal and the second input signal is
applied to the noninverting terminal through a voltage divider. The output voltage is
Vout = (-R2/R1)V1 + ((R1 + R2)/R1)(R4/(R3 + R4))V2.

				
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