Introduction #

A non-inverting amplifier is an operational amplifier configuration in which the input signal is applied directly to the non-inverting terminal of the op-amp.
The output voltage is an amplified replica of the input voltage and remains in phase with it.

This configuration is commonly used in signal-conditioning applications where high input impedance, stable voltage gain, and low signal distortion are required.

Circuit Description #

The non-inverting amplifier uses a resistive feedback network connected between the output terminal and the inverting input of the operational amplifier.

• The input signal is applied to the non-inverting (+) terminal
• The inverting (−) terminal receives a fraction of the output voltage through a voltage divider
• Negative feedback controls the overall gain of the circuit

The feedback network forces the op-amp to operate in its linear region, allowing the gain to be set precisely using external resistors.

Output Waveform Explanation #

The input signal is a sinusoidal waveform applied to the non-inverting terminal.
The output waveform is also sinusoidal and remains in phase with the input signal.

Key observations from the waveform:

• The output amplitude is approximately 11 times the input amplitude
• Both input and output have the same frequency
• No phase inversion is observed
• The waveform remains undistorted, indicating linear operation

This confirms correct non-inverting amplifier behavior and proper negative feedback operation.

Input and Output Characteristics #

Input:

• Input signal is applied to the non-inverting (+) terminal
• Input voltage: sinusoidal signal of ±1 V peak at 1 kHz
• Very high input impedance of the op-amp
• Input current is negligible, resulting in minimal loading on the signal source

Supply Voltage:

• Dual power supply operation
• Positive supply: +15 V
• Negative supply: −15 V
• Supply voltages are sufficient to support the required output swing without saturation

Output:

• Output voltage is an amplified version of the input signal
• Output remains in phase with the input waveform
• Output peak voltage: approximately ±11 V for a gain of 11
• Output swing is limited by the op-amp supply rails and internal output stage

Principle of Operation #

In linear operation, the op-amp output adjusts itself through negative feedback such that the voltage at the inverting terminal follows the voltage applied at the non-inverting terminal.

This behavior is a consequence of:

• Very high internal gain of the op-amp
• The presence of negative feedback

As a result, the feedback network forces a fixed relationship between the input voltage and the output voltage, producing a stable and predictable closed-loop gain.

(The input terminals are not physically shorted; they are driven to nearly the same voltage by feedback.)

Gain Equation #

The closed-loop voltage gain of a non-inverting amplifier is given by:

Gain = 1 + (Rf / R1)

Where:

• Rf is the feedback resistor connected between the output and the inverting input
• R1 is the resistor connected between the inverting input and ground

This expression shows that the gain depends only on the resistor ratio and is independent of the op-amp’s internal gain.

Gain Calculation and Verification #

Given:

• Rf = 10 kΩ
• R1 = 1 kΩ

Calculated gain:

Gain = 1 + (10 / 1)
Gain = 11

For an input voltage of ±1 V:

Expected output voltage = ±11 V

The simulated output waveform confirms this calculated gain, with the output remaining in phase with the input signal.

Applications #

• Voltage amplification with high input impedance
• Sensor and transducer signal conditioning
• Audio and instrumentation pre-amplifiers
• Buffer stages in analog signal chains

Practical Notes #

• Output saturation occurs if the required output voltage exceeds the supply limits
• Gain accuracy depends on resistor tolerance and temperature stability
• Higher gain values reduce the effective bandwidth of the amplifier
• Stability must be considered when operating at higher frequencies