A circuit capable of amplifying a weak signal is called an amplifying circuit or an amplifier. The integrated operational amplifier is a device that uses a multi-stage DC amplifier on an integrated chip, as long as a small number of components are externally connected to perform various functions.
Because it was used in analog computers as an adder and multiplier in the early days, it is called an operational amplifier. It has more than a dozen pins and is generally represented by a triangular symbol with 3 terminals, as shown in Figure 10. It has two inputs and one output. The upper input is called the inverting input and is marked with "-"; the lower input is called the non-inverting input, marked with "+".
The integrated operational amplifier can perform various analog operations such as addition, subtraction, multiplication, division, differentiation, and integration, and can also be connected to an AC or DC amplifier application. When used as an amplifier application:
(1) Non-inverting output amplifier circuit with zero adjustmentFigure 11 shows a non-inverting output op amp circuit with a zeroed terminal. Pins 1, 11, and 12 are zero terminals. Adjusting RP allows the output (8) to output zero voltage when it is static. 9 and 6 are connected to positive and negative power supplies respectively. The input signal is connected to the non-inverting input (5), so the output signal and the input signal are in phase. The amplifier's negative feedback is connected to the inverting input (4) via feedback resistor R2. The voltage amplification factor of the non-inverting input connection is always greater than one.
It is also possible to have the input signal connected from the inverting input, as shown in Figure 12. If the circuit requirements are not high, you can not zero, then you can short the three zero terminals.
The input signal is connected from the coupling capacitor C1 through R1 to the inverting input, and the non-inverting input is grounded through resistor R3. The voltage amplification factor of the inverting input connection can be greater than 1, equal to 1, or less than one.
(3) Non-inverting output high input impedance op amp circuit
In Figure 13, there is no access to R1, which is equivalent to the infinite value of R1. At this time, the voltage amplification factor of the circuit is equal to 1, and the input impedance can reach several hundred kilohms.
Amplification circuit reading map points and examples
Amplifying circuits are circuits that vary more and more complexly in electronic circuits. When you get an enlarged circuit diagram, you must first break it down step by step, then understand the principle of the first-level analysis, and finally comprehensively. Pay attention to when reading the picture:
1 Separate the main components and auxiliary components in the step-by-step analysis. There are many auxiliary components used in the amplifier, such as temperature compensation components in the bias circuit, voltage stabilized current components, anti-vibration components that prevent self-oscillation, decoupling components, and protection components in the protection circuit.
2 The most important and difficult problem in the analysis is the analysis of feedback. It is necessary to find the feedback path and judge the polarity and type of feedback. Especially for multi-stage amplifiers, the negative feedback is often added to the previous stage, so it is more detailed. analysis.
3 Generally, low frequency amplifiers are commonly used in RC coupling mode; high frequency amplifiers are often associated with LC tuning circuits, either with single tuning or with dual tuning circuits, and the capacitors used in the circuits are generally small.
4 Pay attention to the polarity of the transistor and the power supply. Dual power supplies are often used in the amplifier, which is the specificity of the amplifier circuit.
First order bandpass filter consisting of an operational amplifier
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