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If you need to boost a tiny sensor signal without flipping its polarity or draining its current, an inverting amplifier will not work. Instead, you connect your signal directly into the high-impedance terminal of a non-inverting operational amplifier.
How does this circuit amplify a signal without inverting it while keeping gain completely stable?

The Non-Inverting Topology

In a non-inverting amplifier, the input voltage VinV_{in} applies directly to the non-inverting input (++), while a potential divider network routes a fraction of the output back to the inverting input (βˆ’-). A potential divider is simply two series resistors that split a total voltage into a predictable smaller fraction.

How Voltage Feedback Samples the Output

In 1927, Harold Black invented negative feedback to stabilize telephone amplifiers; here, the resistor divider continuously samples VoutV_{out} so that Vβˆ’=Vout(R1R1+Rf)V_- = V_{out} \left(\frac{R_1}{R_1 + R_f}\right). Unlike the inverting amplifier where the (βˆ’)(-) terminal sits at 0Β V0\text{ V}, this setup exhibits virtual equality, where the op-amp actively drives VoutV_{out} until Vβˆ’V_- matches VinV_{in}.

Key takeaways

  • In a non-inverting operational amplifier circuit, the input voltage VinV_{\text{in}} is connected directly to the non-inverting terminal (v+v_+), ensuring the output voltage VoutV_{\text{out}} is in phase with the input (Av>0A_v > 0).
  • A potential divider formed by feedback resistor RfR_f (between output and inverting input) and ground resistor R1R_1 (between inverting input and 0Β V0\text{ V}) samples the output voltage to provide negative feedback to the inverting terminal (vβˆ’v_-).
  • Because an ideal op-amp has infinite input impedance (Rin=∞R_{\text{in}} = \infty), zero current enters the inverting terminal (Iβˆ’=0Β AI_- = 0\text{ A}), meaning the resistors RfR_f and R1R_1 carry the identical series current.
  • The potential divider equation determines the voltage sampled at the inverting node: vβˆ’=Vout(R1R1+Rf)=Ξ²Voutv_- = V_{\text{out}} \left( \frac{R_1}{R_1 + R_f} \right) = \beta V_{\text{out}}, where Ξ²\beta is the feedback fraction.