Operational amplifier circuit: non-inverting amplification or inverting amplification?

“The operational amplifier in the Electronic circuit has a non-inverting input terminal and an inverting input terminal. The polarity of the input terminal and the output terminal are the same polarity is a non-inverting amplifier, and the polarity of the input terminal and the opposite polarity of the output terminal are called inverting Amplifier.

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The operational amplifier in the electronic circuit has a non-inverting input terminal and an inverting input terminal. The polarity of the input terminal and the output terminal are the same polarity is a non-inverting amplifier, and the polarity of the input terminal and the opposite polarity of the output terminal are called inverting Amplifier.

The same direction terminal of the op amp in Figure 1 is grounded = 0V, the reverse terminal and the same direction terminal are imaginary short, so it is also 0V, the input resistance of the reverse input terminal is very high, virtual disconnection, almost no current injection and outflow, then R1 and R2 are equivalent Therefore, in series, the current flowing through each component in a series circuit is the same, that is, the current flowing through R1 and the current flowing through R2 are the same.

The current flowing through R1: I1=(Vi-V-)/R1…a

The current flowing through R2: I2=(V–Vout)/R2……b

V-=V+=0………………c

I1=I2……………………d

Solve the above junior high school algebraic equations to get

Vout=(-R2/R1)*Vi

This is the input and output relationship of the legendary inverting amplifier.

In Figure 2, Vi and V- are virtual short, then Vi=V-……a

Because of the virtual disconnection, there is no current input and output at the reverse input terminal. The currents passing through R1 and R2 are equal. Set this current to I. From Ohm’s law:

I=Vout/(R1+R2)……b

Vi is equal to the partial pressure on R2, namely: Vi=I*R2……c

From the abc formula, Vout=Vi*(R1+R2)/R2, this is the formula of the legendary non-inverting amplifier.

Choice of integrated operational non-inverting amplifier and inverting amplifier[2]

Operational amplifiers can be connected to non-inverting amplification or inverting amplification. Is it better to use non-inverting amplification or inverting amplification? Let’s first look at the difference between in-phase amplification and inverting amplification:

Non-inverting amplifier

Advantages: the input impedance and the input impedance of the op amp are equal, close to infinity

Disadvantages: the amplifier circuit has no virtual ground, so it has a larger common-mode voltage, and its anti-interference ability is relatively poor. It requires a higher common-mode rejection ratio when using the op amp. Another small disadvantage is that the magnification can only be greater than 1;

Inverting amplifier

Advantages: The potential of the two input terminals is always approximately zero (the non-inverting terminal is grounded, and the inverting terminal is virtual ground), only differential mode signals, and strong anti-interference ability;

Disadvantages: The input impedance is very small, equal to the resistance value of the series resistance from the signal to the input terminal.

The other is that the gain calculation formulas of the two are different, and the phase is opposite.

It can be seen that the comparison between them should be in the following aspects: input and output impedance, common mode anti-interference

1. The input impedance of the non-inverting amplifier is equal to that of the op amp, close to infinity. The input resistance of the non-inverting amplifier does not affect the input impedance; and the input impedance of the inverting amplifier is equal to the resistance of the series resistance from the signal to the input. Therefore, when the input impedance is required to be high, a non-inverting amplifier should be selected!

2. The input signal range of the non-inverting amplifier is limited by the common-mode input voltage range of the op amp, while the inverting amplifier has no such limitation. Therefore, if the input impedance is not high and the phase is not required, inverting amplification is preferred, because inverting amplification only has differential mode signals, which has strong anti-interference ability and can get a larger input signal range.

3. When the design requires the same magnification, try to choose a resistor with a small value to cooperate, so that the influence of the input bias current and the influence of the distributed capacitance can be reduced. If you care about power consumption, you have to compromise on the value of the resistance.