Operating Without Feedback

The common configuration of an Op Amp is to include a feedback circuit. Without any feedback, the amplification function, as we know it, ceases and the device operated more like a switch with three output states, low-level, mid-level and high-level output voltage.

General Output Voltage States with Feedback

1) The low output voltage state is when the non-inverting input voltage is below the inverting voltage. This causes the output voltage to decrease, moving very rapidly to a point close to the V- voltage. In this section we will call this State-1.

2) The mid-point output voltage is set somewhere between the rails and the inputs are at the same potential. This will be called State-2.

3) The high output voltage state occurs anytime the non-inverting input voltage is above the inverting voltage. This causes the output voltage to increase, moving very rapidly to a point close to the V+ voltage. In this section, we will call this State-3.

The rate of this rapid change is the Slew rate. There is some Slew information in a few pages.

Unity Gain Amplifier:

The simplest configuration is the unity gain amplifier which has a gain of one(1). What that means is that for every change in the non-inverting input voltage, an identical change occurs in the output voltage level.

Unity Gain Amplifier Characteristics:
1) The output voltage is tied directly back to the inverting pin.
2) The input impedance is very high at over 1M ohm. Impedance is a resistance load for changing voltages. This means that this circuit will not consume much current from the circuit feeding it.
3) The output impedance is low. This means this circuit can supply power to the circuit it feeds.

This amplifier is generally used as a buffer amplifier. It is placed between some input device, like a microphone, and some output device, like a power amplifier. It provides the same output voltage as the input voltage but can deliver more current thus it can boost the power of the signal in order to drive down stream devices without consuming to much power from the input device or input signal.

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