A non-inverting amplifier is a basic electronic circuit configuration used to amplify an input signal while maintaining its original polarity (i.e., the output signal is not inverted compared to the input). It is commonly implemented using an operational amplifier (op-amp) and a few passive components such as resistors. The non-inverting amplifier is widely used in various analog applications, including audio amplification, signal conditioning, and measurement systems.
The basic circuit diagram of a non-inverting amplifier is as follows:
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+Vcc +---Rf--(Output)
| |
Input -----|+ ---
|- |
-|+ |
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GND GND
Here's how the non-inverting amplifier works:
Operational Amplifier (Op-Amp): The op-amp is a high-gain differential amplifier with two inputs, labeled as "+" and "-". It amplifies the voltage difference between these inputs by a large factor (the open-loop gain, typically very high). In the case of the non-inverting amplifier, the "+" input is used as the non-inverting input.
Feedback Resistor (Rf): The feedback resistor connects the output of the op-amp to its non-inverting input. It is usually denoted as Rf. The feedback loop is essential to establish the amplification behavior.
Input Resistor (Rin): The input resistor, usually denoted as Rin, connects the input signal to the non-inverting input of the op-amp. This resistor is often used to control the input impedance of the amplifier.
Ground Connection: The "-" input of the op-amp is connected to ground (GND).
When an input voltage Vin is applied to the non-inverting input of the op-amp, the op-amp will try to make its two inputs equal by adjusting its output voltage Vout. Here's how the circuit operates:
Input Voltage Amplification: The non-inverting amplifier's voltage gain (Av) is determined by the ratio of the feedback resistor (Rf) and the input resistor (Rin) according to the following formula:
Av = 1 + (Rf / Rin)
As long as Rin is not too small compared to Rf, the voltage gain will be greater than 1, resulting in signal amplification.
Virtual Ground: Due to the high open-loop gain of the op-amp, the voltage at the non-inverting input (V+ input) is considered virtually equal to the voltage at the inverting input (V- input). Hence, the non-inverting input is at a virtual ground potential (V+ ≈ V-).
Negative Feedback: The op-amp tries to maintain V+ = V-, so as the non-inverting input goes up (Vin increases), the op-amp's output will increase as well, creating a negative feedback loop. This feedback stabilizes the output and ensures that the amplified output signal follows the input signal.
Output Voltage: The amplified output voltage (Vout) is given by the following formula:
Vout = Av * Vin
Where Av is the voltage gain, and Vin is the input voltage.
In summary, the non-inverting amplifier is a simple and effective circuit that amplifies an input signal while preserving its polarity. The voltage gain is determined by the ratio of the feedback and input resistors.