Question

Describe the operation of a voltage follower (buffer) using an ideal op-amp.

Answer 1

A voltage follower, also known as a unity gain buffer, is a basic and essential circuit configuration using an ideal operational amplifier (op-amp). The primary purpose of a voltage follower is to isolate a high-impedance source from a low-impedance load, ensuring minimal signal degradation while providing a high input impedance and low output impedance. The ideal op-amp has certain characteristics that make the voltage follower possible.

An ideal op-amp possesses the following properties:

Infinite Open-Loop Gain (AOL): The op-amp's open-loop gain is infinitely high. This means that any difference in voltage between its two input terminals will be amplified infinitely.

Infinite Input Impedance: The input impedance of the op-amp is infinitely high. Therefore, no current flows into the input terminals, making the voltage at both inputs the same.

Zero Output Impedance: The output impedance of the op-amp is zero. It can supply or absorb any amount of current required by the connected load without altering its output voltage.

Infinite Bandwidth: The op-amp has an infinite bandwidth, which means it can handle signals of any frequency without attenuation.

Now, let's describe the operation of a voltage follower (buffer) using an ideal op-amp:

The circuit configuration is quite simple and is shown as follows:

lua
Copy code
      +Vcc
        |
    +---|----+
    |   R1   |
    |        |
Vin --| >O---+-- Vout
    |        |
    |   R2   |
    +---|----+
        |
      -Vcc


Here's how it works:

Input Voltage (Vin): The input voltage (Vin) is connected to the non-inverting input terminal of the op-amp.

Feedback Loop: The output of the op-amp (Vout) is connected back to its inverting input terminal, creating a feedback loop.

Virtual Short Circuit: Since the op-amp has infinite open-loop gain, its two input terminals are virtually at the same voltage. This means that the inverting input (V-) is at the same voltage as the non-inverting input (Vin).

Zero Voltage Difference: As a result of the virtual short circuit, the voltage difference between the inverting and non-inverting inputs is practically zero. In other words, the op-amp will attempt to make the voltage at its inverting input identical to the input voltage (Vin).

Unity Gain: The op-amp, with its infinite gain, will ensure that the output voltage (Vout) exactly follows the input voltage (Vin). In other words, Vout = Vin.

High Input Impedance: Because the op-amp's input impedance is infinite, it draws negligible current from the input source, effectively isolating the source from the rest of the circuit.

Low Output Impedance: With zero output impedance, the op-amp can supply or sink any current needed by the load without affecting its output voltage.

In summary, the voltage follower using an ideal op-amp acts as an impedance buffer, providing a high input impedance to the source and a low output impedance to the load, while maintaining an output voltage equal to the input voltage.