The difference between positive and negative amplification performance of operational amplifiers

Jacktang

The difference between positive and negative amplification performance of operational amplifiers [Copy link]

Operational amplifier An operational amplifier (abbreviated as "op amp") is a circuit unit with a very high amplification factor. In actual circuits, it is usually combined with a feedback network to form a certain functional module. It is an amplifier with a special coupling circuit and feedback. Its output signal can be the result of mathematical operations such as addition, subtraction, differentiation, integration, etc. of the input signal. [1] Since it was used in analog computers in the early days to perform mathematical operations, it was named "operational amplifier". The op amp is a circuit unit named from the perspective of function. It can be implemented by discrete devices or in semiconductor chips. With the development of semiconductor technology, most op amps exist in the form of single chips. There are many types of op amps and they are widely used in the electronics industry. As shown in the figure, the op amp has two input terminals a (inverting input terminal), b (non-inverting input terminal) and an output terminal o. They are also called inverting input terminal, non-inverting input terminal and output terminal respectively. When the voltage U- is applied between the a terminal and the common terminal (the common terminal is the point where the voltage is zero, which is equivalent to the reference node in the circuit), and its actual direction is higher from the a terminal than the common terminal, the actual direction of the output voltage U is from the common terminal to the o terminal, that is, the directions of the two are exactly opposite. When the input voltage U+ is applied between the b terminal and the common terminal, the actual directions of U and U+ are exactly the same relative to the common terminal. For the sake of distinction, the a terminal and the b terminal are marked with "-" and "+" respectively, but do not mistake them for the positive and negative polarity of the voltage reference direction. The positive and negative polarity of the voltage should be marked separately or indicated by arrows. Generally, the operational amplifier can be simply regarded as a high-gain direct-coupled voltage amplifier unit with a signal output port (Out) and two high-impedance input terminals of the same phase and the opposite phase. Therefore, the operational amplifier can be used to make the same phase, the opposite phase and the differential amplifier. The power supply mode of the operational amplifier is divided into two types: dual power supply and single power supply. For dual-power supply op amps, the output can vary on both sides of zero voltage, and the output can also be set to zero when the differential input voltage is zero. For op amps powered by a single power supply, the output varies within a certain range between the power supply and ground. The input potential of the op amp is usually required to be higher than a certain value of the negative power supply and lower than a certain value of the positive power supply. Specially designed op amps can allow the input potential to vary in the entire range from the negative power supply to the positive power supply, and even slightly higher than the positive power supply or slightly lower than the negative power supply is allowed. This type of op amp is called a rail-to-rail input op amp. The output signal of the op amp is proportional to the signal voltage difference between the two input terminals. In the audio band, the output voltage = A0 (E1-E2), where A0 is the low-frequency open-loop gain of the op amp (such as 100dB, i.e. 100,000 times), E1 is the input signal voltage at the non-inverting terminal, and E2 is the input signal voltage at the inverting terminal. Operational amplifiers are widely used devices. When connected to appropriate feedback networks, they can be used as precision AC and DC amplifiers, active filters, oscillators, and voltage comparators. Inverting amplifiers Operational amplifiers in electronic circuits have non-inverting input terminals and inverting input terminals. A non-inverting amplifier is one with the same polarity as the output terminal, while an inverting amplifier is one with opposite polarity as the output terminal. An inverting amplifier circuit has the function of amplifying the input signal and inverting the output. An inverting amplifier circuit has the function of amplifying the input signal and inverting the output. "Inverting" means that the positive and negative signs are reversed. This amplifier uses negative feedback technology. Negative feedback means returning part of the output signal to the input. In the circuit shown in the figure, the connection method of connecting (returning) the output Vout to the inverting input terminal (-) through R2 is negative feedback. The operational amplifier has the following characteristics. When the output terminal is not supplied with power supply voltage, the positive input terminal (+) and the inverting input terminal (-) are considered to have the same voltage applied, that is, they can be considered as virtual short circuits. Therefore, when the positive input terminal (+) is 0V, the voltage at point A is also 0V. The input impedance of the operational amplifier is extremely high, and there is basically no current in the inverting input terminal (-). Therefore, when Ie flows from point A to R2, the currents I1 and I2 are basically equal. Based on the above conditions, using Ohm's law for R2, we can get Vout=- I1xR2. I1 is negative because I2 flows out from point A where the voltage is 0V. From another perspective, when the input voltage of the inverting input terminal (-) rises, the output will be inverted and greatly amplified in the negative direction. Since this negative output voltage is connected to the inverting input terminal via R2, the voltage rise of the inverting input terminal (-) will be blocked. The voltages at the inverting input and the non-inverting input both become 0V, and the output voltage is stable. Calculate the gain through the relationship between the input and output in this amplifier circuit. The gain is the ratio of Vout to Vin, that is, Vout/Vin= (-I1xR2) / (I1xR1) =- R2/R1. The gain is -, indicating that the waveform is inverted. Application: Integrator Replace the original inverting amplifier R2 resistor with a capacitor C2. At this time, the relationship between the input signal Vi and the output signal Vo forms an integral relationship. Differentiator Replace the original inverting amplifier R1 resistor with a capacitor C. At this time, the relationship between the input signal Vi and the output signal Vo is transformed into a differential relationship. Adder If the inverting amplifier is slightly changed, the relationship between the input signal and the output signal Vo can be simplified to Vo = - (V1 + V2 + V3 + ... + Vn) if R1 = R2 = R3 = ... = Rn = Rf, forming an addition relationship. The operational amplifier in the electronic circuit has a non-inverting input terminal and an inverting input terminal. The input terminal has the same polarity as the output terminal, which is a non-inverting amplifier, and the input terminal has the opposite polarity to the output terminal, which is called an inverting amplifier. The difference between the in-phase and inverting op amps: 1. The input impedance of the in-phase amplifier is equal to the input impedance of the op amp, which is close to infinity. The value of the input resistance of the in-phase amplifier does not affect the input impedance; while the input impedance of the inverting amplifier is equal to the resistance of the series resistor from the signal to the input end. Therefore, when the input impedance is required to be very high, the in-phase amplifier should be selected! 2. The input signal range of the in-phase amplifier is limited by the common-mode input voltage range of the op amp, while the inverting amplifier has no such limitation. Therefore, if the input impedance is not high and there is no requirement for phase, inverting amplification is preferred, because inverting amplification only has differential signals, has strong anti-interference ability, and can obtain a larger input signal range. 3. In the design, if the amplification factor is the same, try to choose a resistor with a small value, so as to reduce the influence of input bias current and distributed capacitance. If you are very concerned about power consumption, you have to compromise on the resistance value.

star_66666

This information is very good.