Op Amp Open Loop Gain – Op Amp Open Loop Configuration

What is an Operational Amplifier (Op Amp)?

Basically, the op-amp is a device that amplifies the difference between its two inputs, with high gain, very high input impedance (greater than 1 mega-ohm), and low output impedance (from 8 to 20 ohms).

With these characteristics, it follows that the input currents are practically zero and that it can deliver relatively high output current (see manufacturer’s data).

An operational amplifier consists of many transistors, resistors, capacitors, etc.

The + terminal is the non-inverting terminal. The – terminal is the inverting terminal. There are several types of op amp packages, such as the 8-pin dual in-line (DIP) package (see the figure above).

To determine which pin #1 is, there is a notch between pins 1 and 8, where #1 is the pin to the left of the notch when the integrated circuit is placed as shown in the diagram.

The distribution of the op amp pins in the 8-pin DIP integrated circuit is as follows:

• Pin 1 is offset zero.
• Pin 2 is an inverting input (-).
• Pin 3 is non-inverting input (+).
• Pin 5 is offset zero.
• Pin 6 is the output voltage.
• Pin 8 is not connected.

IC 741 Op Amp Pinout

To power an op amp, 2 power sources are needed:

• Pin 4 is -V power supply (-VCC)
• Pin 7 is +V power supply (+VCC)

What is an Op Amp Open Loop Gain?

The open loop gain of the op amp is given when there is no feedback path between the output and either input. See the figure below.

The open loop gain of the amplifier is given by the following formula AV = Vout / Vin

where:

• AV = voltage gain
• Vout = output voltage
• Vin = input voltage = (V₊ – V_–)

In an ideal op amp, the open loop gain (the gain of the op amp) is infinite. Since the op amp is real, its gain is between 20,000 and 200,000 (in the 741C op amp). This type of configuration is used in comparators where you want to know which of the two inputs has the highest voltage.

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Note: Op Amp = Operational Amplifier