How do you calculate the gain of an op-amp in a non-inverting amplifier with positive feedback?
1 Answer
An op-amp used in a non-inverting amplifier configuration with positive feedback is commonly referred to as a "non-inverting amplifier with voltage divider feedback" or "Schmitt trigger" configuration. This configuration can be used to create a circuit with hysteresis, which is often used in applications such as signal conditioning, threshold detection, and waveform shaping.
To calculate the gain of this circuit, you need to consider both the voltage divider formed by the feedback resistors and the inherent amplification characteristics of the op-amp. Let's break down the steps to calculate the gain:
Feedback Network:
In a non-inverting amplifier with voltage divider feedback, the feedback network consists of two resistors: Rf (feedback resistor) and R1 (input resistor). The voltage divider formed by these resistors determines the feedback ratio and thus affects the overall gain.
Gain Calculation:
The gain (A) of the non-inverting amplifier with positive feedback can be calculated using the following formula:
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A = 1 + (Rf / R1)
Where:
A is the voltage gain of the amplifier.
Rf is the feedback resistor (connected between the output and the inverting input of the op-amp).
R1 is the input resistor (connected between the non-inverting input of the op-amp and the input signal source).
Inherent Op-Amp Gain:
Keep in mind that the op-amp itself has an open-loop gain (A_OL) which can be very high (in the range of tens of thousands to hundreds of thousands). However, the closed-loop gain (A) you calculated above will generally be limited by the power supply voltage and the output voltage swing capabilities of the op-amp.
Hysteresis (if applicable):
If the circuit is intended to have hysteresis (Schmitt trigger functionality), you can introduce positive feedback by adding an additional resistor divider network between the inverting input and the output. This hysteresis feedback modifies the switching thresholds of the circuit.
Remember that in practical applications, you need to select appropriate resistor values for Rf and R1 based on your desired gain and the op-amp's specifications. Additionally, consider factors such as input bias current, common-mode rejection, and output saturation when designing the circuit.
Keep in mind that while the term "non-inverting amplifier with positive feedback" is used in the context of Schmitt triggers, it may differ slightly from the traditional non-inverting amplifier concept, which typically uses negative feedback to provide stable and controlled amplification.
To calculate the gain of this circuit, you need to consider both the voltage divider formed by the feedback resistors and the inherent amplification characteristics of the op-amp. Let's break down the steps to calculate the gain:
Feedback Network:
In a non-inverting amplifier with voltage divider feedback, the feedback network consists of two resistors: Rf (feedback resistor) and R1 (input resistor). The voltage divider formed by these resistors determines the feedback ratio and thus affects the overall gain.
Gain Calculation:
The gain (A) of the non-inverting amplifier with positive feedback can be calculated using the following formula:
css
Copy code
A = 1 + (Rf / R1)
Where:
A is the voltage gain of the amplifier.
Rf is the feedback resistor (connected between the output and the inverting input of the op-amp).
R1 is the input resistor (connected between the non-inverting input of the op-amp and the input signal source).
Inherent Op-Amp Gain:
Keep in mind that the op-amp itself has an open-loop gain (A_OL) which can be very high (in the range of tens of thousands to hundreds of thousands). However, the closed-loop gain (A) you calculated above will generally be limited by the power supply voltage and the output voltage swing capabilities of the op-amp.
Hysteresis (if applicable):
If the circuit is intended to have hysteresis (Schmitt trigger functionality), you can introduce positive feedback by adding an additional resistor divider network between the inverting input and the output. This hysteresis feedback modifies the switching thresholds of the circuit.
Remember that in practical applications, you need to select appropriate resistor values for Rf and R1 based on your desired gain and the op-amp's specifications. Additionally, consider factors such as input bias current, common-mode rejection, and output saturation when designing the circuit.
Keep in mind that while the term "non-inverting amplifier with positive feedback" is used in the context of Schmitt triggers, it may differ slightly from the traditional non-inverting amplifier concept, which typically uses negative feedback to provide stable and controlled amplification.