A differential amplifier (DL) is used to amplify the difference between two input signals. It can be considered as an analog circuit consisting of two inputs and one output.
Amplifiers used in various electricaland electronic circuits for generating signals and performing mathematical operations are called opamps (op amps). They are key components of an electronic analog computer. Their invention in the early 1940s led to the replacement of mechanical counting devices with quiet and fast electronics. Many analog computers relied on vacuum tubes available from George Philbrick's company in 1952.
In 1963, Bob Widlar at Fairchild Semiconductor made an op amp on a single integrated circuit A702 - the very first monolithic IC operational amplifier.
Differential operational amplifier can be assembled according to the scheme, as shown in the figure below, which consists of two transistors T1 and T2.
In the remote control scheme there are two inputs I1 and I2 and two outputsV1out and V2out. Input I1 is fed to the base terminal of the transistor T1, input I2 is fed to the base terminal of the transistor T2. The emitter outputs of the transistor T1 and the transistor T2 are connected to a common emitter resistor. Thus, the two input signals I1 and I2 will affect the outputs V1out and V2out. The circuit consists of two Vcc and Vee supply voltages, but there is no grounding pin. Even with one supply voltage, the circuit can work normally (similarly, using two supply voltages). Therefore, the opposite points of the positive voltage and negative voltage supply are connected to ground.
The operation of the differential amplifier is shown in the diagram in the figure below.
If the input signal (I1) is fed to the basethe transistor T1, then through a resistor connected to the transistor transistor T1, there is a positive voltage drop, which will be smaller. If the input signal (I1) is not supplied to the base of the transistor T1, then a positive voltage drop will appear through a resistor connected to the transistor T1, which will be large.
It can be said that the inverting output coming outthrough the collector terminal of the transistor T1, based on the input signal I1 supplied to the base terminal T1. If T1 is turned on by applying a positive value of I1, then the current passing through the emitter resistance increases when the emitter current and collector current are almost equal. If the voltage drop on the emitter resistance increases, then the emitter of both transistors goes in the positive direction. If the emitter of the transistor T2 is positive, then the base of T2 will be negative, and in this state the current will be less. And there will be less voltage drop across the resistor connected to the collector contact of the transistor T2.
Therefore, for this positivecollector input signal T2 will go in the positive direction. It can be said that the non-inverting output arising at the collector terminal of the transistor T2 is based on the input signal supplied to the base T1. The differential amplifier takes the output signal between the collector pins of the transistors T1 and T2. From the above concept, it is assumed that all characteristics of transistors T1 and T2 are identical, and if the base voltages Vb1 are equal to Vb2 (the base voltage of transistor T1 is equal to the base voltage of transistor T2), the emitter currents of both transistors will be equal (Iem1 = Iem2).
Thus, the total emitter current will be equal tothe sum of the emitter currents T1 (Iem1) and T2 (Iem2). Calculation of the differential amplifier. Iem1 = Iem2 Ie = Iem1 + Iem2 Vev = Vb-Vb em I em = (Vb-Vb em) / Rem. Thus, the emitter current remains unchanged regardless of the hfe value of the transistors T1 and T2. If the resistances connected to the collector terminals T1 and T2 are equal, then their collector voltages are also equal.
This amplifier (Op-amp, English version) canbe perfect with infinite gain and bandwidth when used in open-loop mode with a typical DC gain greater than 100,000 or 100 dB. Differential amplifier current OU has two inputs, one of which is inverted. The amplified difference of these inputs is output as voltage. The ideal op amp has an infinitely high gain. This should express the symbol of infinity with the new symbol. The op amp operates either with a double positive (+ V), or with a corresponding negative (-V) power supply, or it can operate on a single DC supply voltage.
They are that such an amplifier hasinfinite input impedance (Z = ∞), which leads to the absence of current flowing into one of its two inputs and zero input bias voltage V1 = V2. The op amp also has zero output impedance (Z = 0). Optical amplifiers determine the difference between the voltage signals applied to their two input terminals, and then multiply them by some predetermined gain (A). This gain (A) is often called - Open Loop Ratio. OA can be connected in two basic configurations - inverting and non-inverting.
For negative feedback if voltagefeedback is in antiphase at the input, the overall gain is reduced. For positive feedback, when the feedback voltage is in the "phase", the input signal of the amplifier increases. By connecting the output back to the negative input connector, 100% feedback is achieved, with the result that the voltage follower circuit (buffer) is obtained with a constant gain of 1 (Unity). By replacing the fixed feedback (Rƒ) resistor for the potentiometer, the circuit will have an adjustable gain factor.
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The principle of its operation is shown in the diagram below.
It is built using two matchingtransistors in the general configuration of an emitter whose emitters are connected to each other. A simple circuit capable of amplifying small signals between two inputs, but suppressing the noise signals common to both inputs.
Differential amplifier on bipolartransistors (BJT) has a unique topology: two inputs and two outputs. Although it is possible to use a signal from only one output, the difference between both outputs provides twice as much gain! And this improves common mode suppression (CMR) when the common mode signal is a noise source or a DC offset from the previous step.
Based on input and output data entry methods, differential amplifiers can have four different configurations, as shown below.
When developing analog building blocks(various types of preamplifiers, filters, etc.) it is important, along with the development of modern solutions for deep submicron technologies, to pay attention to new structural solutions of traditional amplifying devices.
Dc differential amplifier(DUPT), its output voltage is proportional to the difference between the two input voltages. This can be represented in the form of an equation as follows: V out = A * ((Vin +) - (Vin-)), where A = gain.
In practical schemes, the remote control is used to amplify: pulses over long wires, sound, radio frequencies, control of motors and servomotors, electrocardiograms, information on magnetic drives.
The differential amplifier has a number of drawbacks, somewhat limiting its use in electronics:
