Operational amplifier parameter analysis and LTspice application simulation" Reading notes 1 Remember the gap between ideal and reality

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Operational amplifier parameter analysis and LTspice application simulation" Reading notes 1 Remember the gap between ideal and reality

Ideal amplifier:

1 The open-loop differential-mode voltage gain is infinite.

2 The differential mode input resistance is infinite.

3 No input bias current.

4 No input offset voltage.

5 Common-mode rejection ratio is infinite.

6 The output resistance is infinitesimally small.

7 -3dB cutoff frequency is infinitely high.

8 There is no voltage inside, no current noise, and is not affected by temperature.

A real amplifier is an artificial amplifier

The above 8 points are exactly what we should pay attention to when using:

1 What is the open-loop differential-mode voltage gain?

2 How big is the differential input resistance?

3 How large is the input bias current?

4 How big is the input offset voltage?

5. What is the common mode rejection ratio?

6. How big is the output resistance?

7 What is the -3dB cutoff frequency?

8 What are the effects of internal voltage, current noise, and temperature?

The basic components of the amplifier:

Input stage Intermediate stage Output stage

Bias Circuit

The input stage is composed of a differential amplifier circuit, and as long as the input impedance is high, the common-mode suppression capability is strong, the noise suppression capability is strong, and the quiescent current is small.

Intermediate stage amplification is the main purpose.

The output stage adopts complementary symmetrical amplifier circuit to achieve low output impedance, high driving capability, current limiting, short circuit protection, etc.

The bias circuit provides DC operating current and voltage for each stage.

Amplifier Category:

Classified by production process: bipolar, Bi-FET, coms, special type with combined structure

Classification by parameters: general-purpose amplifiers and special-purpose amplifiers (instrumentation amplifiers, fully differential amplifiers, transimpedance amplifiers, current sensing amplifiers, etc.).

Amplifier feedback mode: positive feedback negative feedback

Positive feedback: A resistor is connected between the positive input stage and the output of the op amp, and then a resistor is connected between this stage and the ground, forming a circuit in which the output signal is fed back to the positive input stage.

Negative feedback: A resistor is connected between the negative input stage and the output of the op amp, and then a resistor is connected between this stage and the ground, forming a circuit in which the output signal is fed back to the negative input stage.

target512

I have learned a lot. The OP's analysis is very accurate. This classic should not be missed. Thank you very much.

annysky2012

Ideals are full of hope, but reality is very hard. But having ideals is very helpful to reality, at least we know the approximate result.