"One week's work on Analog Electronics" - integrated operational amplifier

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Preface

Integrated operational amplifier is a multi-stage direct coupled amplifier with high amplification factor , Is the earliest development , One of the most widely used analog integrated circuits .
characteristic ： High gain 、 high reliability 、 Low cost 、 Small size
I have a blog that explained the principle of operational amplifier 、 In phase proportional amplifier circuit and reverse proportional amplifier circuit , And the addition, subtraction, multiplication and division amplifier circuit based on the operational amplifier , So I won't explain this time , Introduce several circuits that are not explained .

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One 、 Unipolar and bipolar conversion circuit

1. Bipolar to unipolar conversion circuit

2. Unipolar to bipolar conversion circuit

Two 、 Instrument amplifier circuit

3、 ... and 、 Triangular wave generation circuit

The first op amp is a positive feedback , So the op amp works in the nonlinear region ; The operational amplifier of the subsequent circuit constitutes an integral operational amplifier circuit .

The first op amp output is a rectangular wave , As shown in the figure below ：

Then the output of the second op amp is triangular wave , As shown in the figure below ：

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Four 、 Active power filter

The simulation diagram of active low-pass filter is as follows ：

measurement R1 and C1 The amplitude frequency characteristic curve of the passive first-order low-pass filter is as follows ：

measurement R1、C1、R2 and C2 The amplitude frequency characteristic curve of the passive second-order low-pass filter is as follows ：

The amplitude frequency characteristic curve of the active second-order low-pass filter with the operational amplifier is as follows ：

According to the above simulation diagram , Increasing the filter class can narrow the transition band , As the order increases, it gradually approaches the rectangle .
Adding an op amp can make RC Passive filter has good frequency selectivity , And use op amp to solve the problem of energy consumption caused by resistance .

5、 ... and 、 Sample and hold circuit

Sample and hold circuit , be chiefly used in AD Before switching the circuit , It can collect the input signal at a certain moment .

Sample and hold circuit simulation diagram ：

6、 ... and 、 Venturi bridge oscillation circuit

The simulation circuit diagram is as follows ：
The output signal is ：

The output signal is relatively small , The diode is not conducting , Then the resistance of the feedback terminal is 670K, The magnification is 7.7, Greater than 3;
Output signal becomes larger , The diode starts to turn on , The feedback resistance is no longer 670K, But gradually become 200K, So as to achieve stability .
therefore R3 Control the starting vibration speed ;R4 Control the starting amplitude value , No more than 200;
R3 The bigger it is , The faster the vibration starts ;

7、 ... and 、 Voltage comparator

An ideal op amp has no negative feedback loop , It works in the nonlinear region , It can be used as a voltage comparator .
The simulation diagram is as follows ：