# Op-Amp Current Gain with current source

• gfd43tg
In summary, The conversation is about problem #6 and the equations involved in solving it. The main issue is determining the current flow through the different components, specifically Rf and Rs. The solution involves using the fact that the voltage at the negative node of the op-amp is zero and that no current can flow through Rs in an ideal steady state. This leads to the final solution of G = -Rf/RL, which is the gain of the inverting amplifier.
gfd43tg
Gold Member

## Homework Statement

Problem #6 on the attachment

## The Attempt at a Solution

I am stuck because if I do KCL at the node above the current source, It seems like all of the current should go back into Rs and none from the current source goes up to Rf

#### Attachments

• 5.6.jpg
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Last edited:
You forgot the attachment but I found it on another thread.

The current through Rf is typically written as (Vo-Vi)/Rf.

There are two sources of current into Rs, not just one!

EDIT: donpacino is right. No current into Rs.

Last edited:
you want iL/is

with negative feedback, the positive and negative nodes of the op-amp should equal each other. so the negative node=0V

since the voltage at the negative node is zero, with an ideal steady state op-amp no current can flow through Rs.

so the current through rf is Is.

Use that to get you started

1 person
I have it solved, thank you!

I got G = -Rf/RL

## 1. What is an op-amp?

An op-amp, short for operational amplifier, is an electronic device that amplifies the difference between two input voltages. It is commonly used in electronic circuits to perform mathematical operations such as addition, subtraction, and integration.

## 2. How does an op-amp work?

An op-amp is made up of transistors, resistors, and other electronic components. It has two inputs, a non-inverting input (+) and an inverting input (-), and one output. The output voltage is determined by the voltage difference between the two inputs and the characteristics of the op-amp itself.

## 3. What is current gain in an op-amp?

Current gain is a measure of how much the output current of an op-amp is amplified compared to the input current. It is typically denoted as Ai and is defined as the ratio of output current to input current.

## 4. What is a current source and how does it affect op-amp current gain?

A current source is an electronic circuit element that provides a constant amount of current to a circuit. In op-amp circuits, a current source can be used to provide a steady input current to the op-amp, which in turn affects the current gain of the op-amp. By using a current source, the input current to the op-amp can be controlled and kept constant, resulting in a more stable and predictable output current.

## 5. How is current gain calculated in an op-amp with a current source?

In an op-amp circuit with a current source, the current gain (Ai) can be calculated by dividing the output current (Iout) by the input current (Iin). This can be expressed as Ai = Iout / Iin. The value of Ai can be affected by the characteristics of the op-amp, the circuit design, and the value of the current source.

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