Operational Amplifier (Op-Amp)

The operational amplifier is an electronic circuit that is widely used in many practical electronic systems such as TV’s, stereos, phones, control systems, medical equipment, etc.

Main Operations of Op-Amp:

• Amplification
• Addition
• Subtraction
• Differentiation
• Integration
• Filtering
• Many more, including non-linear operations

Inverting amplifier?? → this is when the output voltage is inverted (opposite sign).

Symbol Conventions Explained

• $v_p$ is positive voltage
• $v_n$ is negative voltage
• $v_o$ is like output voltage
• Positive DC Power Supply ($V_{CC}$)
• Negative DC Power Supply ($-V_{EE}$)

Other

• $v_i$ is like input voltage, also written as $v_d$, equal to $v_i=v_p-v_n$

We don't draw the power supply inputs of the op amp usually to prevent clutter in the schematic, but it is there.

Non-Ideal Op-Amp Model

Ideal Op-Amp Model

If we assume it is an ideal op-amp, it makes the analysis of op-amp circuits very easy and quick.

Assumptions

1. We assume Input resistance $R_i$ is very large, so $i_p=i_n=0$
2. Voltage gain $A$ is very large, so $v_p=v_n$

Finding Output voltage $v_o$

Sometimes, in the question, they might ask to give the output voltage.

This is as simple as $v_0=A{v}_{in}$, where $A$ is the voltage gain.

However, you need to make sure that $-V_{EE}\le v_0\le +V_{cc}$ If it is not met, you use whichever one saturates.

Ex: if you calculate $v_0=-15V$ but $V_{E}E=10V$, then the output saturates at $v_0=-10V$

Voltage Transfer Characteristics

The non-ideal/ideal op-amps described above are created based on the properties described below.

I still don’t understand a lot, but I am writing these notes hoping to extend on them in the future.

The Op-Amp only operates at certain voltages. It must satisfy: $|v_i|\le 0.1mV$

This implies that $v_p\approx v_n$ (condition for linear region)

The gain $A$ is how much the voltage is gained $A=\frac{v_0}{v_i}$

$A$ represents this slope. Ideally, this slope is infinite so we instantly go from negative saturation to positive saturation.

The reality is represented by the graph below.

title: I don't understand how op-amps work lol #gap-in-knowledge 
I still don't understand.
 
What is the purpose of an op-amp?
 
I know perfectly well how to solve a circuit assuming that it is an ideal op-amp, but I don't understand why it works.
 
i.e. how does Voltage gain work? How do we design op-amps with the right voltage gains?

Related

Think about the difference between this and Buck Converter / Buck Converter / Boost Converters. There’s several differences as explained in this reddit post.