In-phase and out-of-phase amplification of operational amplifiers

Jul 14, 2025#电路12

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The document discusses operational amplifiers (op-amps), focusing on inverting and non-inverting amplifiers. 1. **Inverting Amplifier**: When the non-inverting terminal is grounded (0V), the inverting terminal also approximates 0V due to virtual shorting, resulting in the output voltage relationship: \[ V_{out} = -\frac{R_2}{R_1} \times V_i \] 2. **Non-Inverting Amplifier**: Similarly, the output voltage relationship is given by: \[ V_{out} = \frac{R_1 + R_2}{R_2} \times V_i \] 3. **Advantages and Disadvantages**: - **Inverting Amplifier**: - **Pros**: Input terminals are nearly at 0V, strong noise immunity. - **Cons**: Low input impedance, equal to the series resistance at the input. - **Non-Inverting Amplifier**: - **Pros**: High input impedance. - **Cons**: Lacks virtual ground, higher common-mode voltage, and poorer noise immunity. In applications where high input impedance is not critical and phase is not a concern, the inverting amplifier is preferred for its strong noise immunity and larger input signal range. In designs requiring the same gain, smaller resistor values are recommended to minimize the effects of input bias current and parasitic capacitance.

1 Inverting Amplifier#

The non-inverting terminal is grounded, with a voltage of 0. The inverting and non-inverting terminals are virtually shorted, so the voltage is also 0 V. Due to the virtual break, there is almost no current injected, so R1 and R2 are effectively in series, and the current through the resistors is equal.

Thus, the input-output relationship can be expressed as

V_{out}=-\frac{R_2}{R_1}\times V_i

2 Non-Inverting Amplifier#

Similarly, based on the virtual break and virtual short, the input-output relationship can be expressed as

V_{out}=\frac{R_1+R_2}{R_2}\times V_i

3 Advantages and Disadvantages of Non-Inverting and Inverting Amplifiers#

3.1 Inverting Amplifier#

Advantages: The potentials at the two input terminals are always approximately 0, with only differential mode signals, strong anti-interference capability.
Disadvantages: The input impedance is low, equal to the series resistance value of the signal to the input terminal.

3.2 Non-Inverting Amplifier#

Advantages: The input impedance is close to infinity.
Disadvantages: The amplification circuit does not have a virtual ground, has a large common-mode voltage, poor anti-interference capability, and requires the operational amplifier to have a high common-mode rejection ratio.

If a low input impedance is acceptable and there are no phase requirements, the inverting amplifier is preferred because it only has differential mode signals, strong anti-interference capability, and can achieve a larger input signal range.

In design, when the amplification factor is required to be the same, it is advisable to choose smaller resistor values to reduce the impact of input bias current and distributed capacitance.