amplifier is a device that can amplify the voltage or power of the input signal. It consists of electronic tube or transistor , power transformer and other electrical components. It is used in various devices such as communication, broadcast, radar , television, automatic control, etc.
First, understand the amplifier first. The amplifier can be represented by a triangle symbol in the circuit diagram. The tip end is the output terminal (OUT) and the other end is the input terminal (IN) . Sometimes a box is also drawn, and a triangle is drawn inside, and the triangle represents the amplifier. Symbols only represent amplifiers. No matter what form of circuit the amplifier is, electronic tubes, transistors, , discrete components, integrated modules, etc. can all use a triangle to represent amplifiers.
symbol only represents the amplifier, and does not represent any form of amplifier.
Amplification circuit of transistor
can simplify the transistor amplification circuit, the field effect transistor amplification circuit, the power amplifier circuit, etc. into a triangle symbol. In this way, does not have to draw the internal components , but can represent that this circuit has the function of amplification . In addition to the input and output terminals of the
amplifier, other functional pins can be drawn next to it, such as the power pin can be drawn next to it. The amplifier uses dual power supply , connected to positive and negative power. For amplifiers that power with dual power supply, the input and output do not usually require coupling capacitors because when static, their voltage is zero volts.
When using a single power supply, the top is positive and the bottom is negative, but the connection method of a single power supply is generally ground line . At this time, the static voltage at the output or input terminal is often half of the power supply voltage, at least it is not zero volts, so the capacitor is needed to couple to interchange with DC.
Sometimes you will see two different symbols inside the integration module. The difference from the previous one is that there is an extra circle on the OUT end of the amplifier on the right, which represents reverse amplification of , and the previous one is the in-phase amplifier.
can be understood as the change law of the output end of the in-phase amplifier and the change law of the input end are the same. When the input rises, the output also rises, the input falls, and the output also falls, that is, the forward bit of amplifies ; while the reverse amplification is just the opposite, the change direction of the voltage at the output end is the opposite of the input end, the voltage at the input end rises, the voltage at the output end drops, the voltage at the input end drops, and the voltage at the output end rises, that is, the reverse bit of amplifies .
In-phase amplification : The change direction of the output end is the same as the change direction of the input end, which is the phase difference of zero degree;
Inverse phase amplification : The change direction of the output end is opposite to the change direction of the input end, which is a phase difference of 180°;
For the in-phase amplifier, its input voltage will also rise, and the synchronous change is only due to the amplification effect, the change amplification of the output end is larger. The amplification actually controls the large with a small voltage or current, and it is used to call it amplification effect; when the voltage at the input end of the inverting amplifier is converted, the direction of the output end is opposite to it, and it changes synchronously. The method of identifying an in-phase amplifier is to mark an "IN+" at the input end, or directly mark a "+" sign; there are two identification methods for inverted phase amplifiers, as shown in the picture on the right, one is to mark a circle at the OUT end, and the other is to mark an "IN-" on the left, or mark a "-" sign.
When we put the in-phase amplification and inverse amplification functions together, we form operational amplifier . Of course, there are not two independent amplifiers in it, but first compare the voltage difference between the two pins and then amplify it. When the voltage changes at both inputs, it will have an impact on the output. It depends on which of the voltage changes more significantly, and whoever controls the outputs will play a leading role. Below are the basic symbols of the op amp.
Its main function is to compare the voltages of the two pins IN+ and IN-, and then amplify their difference , and then output. First of all, the first point is that the operational amplifier has a very high amplification factor. Regardless of current amplification or voltage amplification, the amplification factor of conventional operational amplifiers is generally above 10,000 times, and 50,000 or 60,000 times is normal. The commonly referred to as open-loop amplification means no feedback (regardless of positive feedback or negative feedback), that is, the amplification factor in the absence of feedback is the amplification of the difference between the two voltages at the input.
The actual operational amplifier can only have a very high amplification, while the ideal operational amplifier for should be an infinite amplification . That is to say, I hope the amplification magnification of the operational amplifier is very large, so large that it does not affect our calculation of the circuit. Therefore, many calculation formulas calculate the amplification magnification of the operational amplifier as infinity. Sometimes when you see this symbol appearing in the circuit diagram, a box represents a module, and the triangle inside represents the amplifier, and the symbol behind it is infinite, that is, the amplifier's amplification is infinite. Only an ideal amplifier has an infinite amplification. The actual amplifier's amplification will not be infinite, but such a symbol will appear in the circuit diagram, that is, the circuit design is designed according to the amplifier's amplification infinity.
Op-amp belongs to a comparison amplifier. It mainly compares the voltages at the two input terminals and amplifies their voltage difference. The output voltage is equal to
Because the open-loop amplification ratio of the operational amplifier is very large, it is possible to output a very high output voltage after calculation. However, the actual voltage of cannot be very high, and it will be limited by the power supply voltage and will not be higher than the power supply voltage . For example, the output voltage is calculated to be 20V, but in fact it should not be 20V, because it will be limited by the power supply. If the power supply is 12V, the output voltage will not exceed 12V. Some op amps have outputs that can reach the power supply voltage, but some can only approach the power supply voltage.
. For an ideal operational amplifier, its amplification is infinite, the voltage in the same phase is higher than the voltage in the inverse phase, and after amplification, it outputs the most likely voltage of , ; the voltage in the same phase is lower than the voltage in the inverse phase, and after amplification, it outputs the most likely voltage of , .
