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ð Introduction & Introduction
Operational amplifiers are often called “operational amps,” and they are amazing things. Because it can amplify the voltage at the input by tens of thousands of times. Specific theoretical magnification is: 100,000 ~ million times. Operational amplifiers are called operational amplifiers because they were originally used in addition, subtraction, differentiation, and integration analog circuits. That’s why it’s called an operational amplifier.
The operational amplifier is an electronic integrated circuit (****) containing multistage amplifier circuit. Its input stage is a differential amplifier circuit, which has high input resistance and zero drift suppression capability. The middle stage is mainly for voltage amplification, with high voltage amplification, generally composed of common emitter amplifier circuit; The output pole is connected to the load and has the characteristics of strong carrying capacity and low output resistance. Operational amplifiers are widely used.
Differential amplifier: differential amplifier circuit is also known as differential amplifier circuit, when the circuit’s two input voltage is different, the output voltage is changed, so called differential. Differential amplifier circuit is by the static working point stability (the actual role is to control the static value of voltage and current) of the amplifier evolved from the differential amplifier is only the input to use a lot of components, these components together constitute the differential amplifier. This makes your input impedance very high and also makes the circuit more resistant to interference, its impedance can be regarded as infinite, which is this part of the resistance that we can equivalent to an infinite. Benefits: The benefit of this design is that the input signal is not affected.
ð How operational amplifiers work
An operational amplifier is a device with three signal input terminals and two power terminals. In the operational amplifier, there are two input terminals and one output terminal. Operational amplifiers also have two terminals for device power supply. As shown below:
Current never flows in or out of the input; it can flow in and out of the output.
The current flowing out of or from the output is supplied by the power supply of the operational amplifier.
The op amp subtracts the voltage input with the “+” from the “-” input. The operational amplifier will take this difference between the two input voltages. And if you multiply it by a very large number, you get a result. In the textbook, the voltage at the output is equal to the voltage difference between the two inputs by a large coefficient K.
For example: the positive end is 0.5V, the negative end is 0.3V. So 0.5 minus 0.3 x 100,000 = 20,000 v
Of course, it is impossible for us to output 20000V at the output end of the actual circuit. At this time, if the power line at both ends of the middle is assumed to be 10V at the positive power supply end, then its actual output voltage is also 10V. Enter the saturation state. So what do we do when we’re all saturated because op-amps aren’t going to work very well.
ðĨ Voltage follower
Let’s connect the output to the negative. Let’s say our output is 0.6V. So after one cycle, the output will go down. Vo = 0.5 V
Assuming that the output is 0.4V, the output will rise again after one cycle.
So that the final Vo output value will be infinitely close to the value of Vp at the positive input. In this case it’s 0.5V. So Vp is equal to Vo is equal to Vn. This is the basic model of the voltage follower.
ðĨ Two features
This model can be used for circuits with high voltages. Steady output to the desired voltage. Note: the output (Vo) and input (Vn) will not be destroyed, because the impedance input end of the op-amp, the impedance is infinite, so large that we can not input the current. This is the characteristic fault of an op amp. Thus: the operational amplifier is isolated, to avoid the burning of the circuit.
And the voltage at the input is the same as the voltage at the Vn, which means it has a short circuit, which means it has almost no voltage. However, op amps still work normally, which is the second feature of op amps. Note: Virtual shortness can only be used with negative feedback.
** Definition: ** To send part or all of the output signal of a system back to the input end of the system as part of the input signal in a certain manner and path, this action process is called feedback. According to the polarity of the feedback signal, feedback can be divided into positive feedback and negative feedback.
So Vo(output) = Vp x (1+R2/R1)
ð Expand your knowledge
Again to introduce the most commonly used several operational knowledge points :(from baidu encyclopedia)
Inexpensive operational amplifiers commonly used are the LM324/358. Common high input impedance (impedance values are usually very high) operational amplifiers are CA3140, TL072. Commonly used high speed operational amplifiers are AD8052, OP37 and LM4562. If used for hi-fi, here recommend you to use LM4562, its working voltage range is wide, high precision! (They are also usually more expensive)
The LM4562 is a high-fidelity dual operational amplifier introduced by National Semiconductor corporation in recent years. Its distortion is very small, only 0.00003%** of total harmonic distortion and noise (THD+N), in other words, the operational amplifier distortion is almost negligible.
The LM4562 chip has the advantages of very low distortion rate, low noise, high conversion rate, wide operating voltage range and large output current, etc., the performance is unprecedented. Because of these advantages, the operational amplifier is suitable for professional and high-end audio systems, such as audiovisual system receivers, preamplifiers, audio decoders and hi-fi amplifiers, as well as a variety of medical imaging systems and industrial equipment.
The LM4562 features a high-speed 6MHz unit gain bandwidth operational amplifier and a proprietary stereo audio driver amplifier. In standard operating conditions, the operational amplifier has an input noise density as low as 2.7nV/âHz, a noise corner at an intermediate frequency of 60Hz, an output current of 26mA, and can drive a 600 Ï load. The LM4562 chip has a conversion rate of 20V/Ξs and a gain bandwidth product of 55MHz. The LM4562 chip can operate stably in supply voltage ranges from Âą2.5V to Âą17V, with a maximum output current of 45mA. The common mode rejection ratio (CMRR) and power rejection ratio (PSRR) of the input circuit are above 108dB and the input bias current is as low as 10ΞA(typical value) when the chip is operated in the above supply voltage range.
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