pp 82-90
4.1 Introduction
O Operational Amplifiers (TE) is one of the most useful active electronic components used in analog electronic circuits at low and medium frequencies. The Operational enichytes owe their name to the fact that in combination with a minimum
number of external components (resistors, capacitors, etc.) can be made ie are a variety of linear and nonlinear functions. They find applications in signal devices such as amplifiers, filters, limiters, composers [synthesizers], etc., in telecommunications circuits (oscillators, modulators, demodulators, phase loops clavicle, etc.), conversion of analog and digital signals (both A / D and D / A) and circuits that perform various mathematical operations (integrators, multipliers, additional, subtractors, etc.).
Typically, the operational amplifier is a dc amplifier large payment usually consists of one or more differential amplifiers followed by a grade level and finally conversion of the output stage. The Sch.4.1 block diagram showing an operational amplifier. The first stage is a differential amplifier with double entry and provide more aid to the TE. In most amplifiers, the intermediate level and is it by double entry, but asymmetrical in the output (ie an exit). Because amplifier is dc,
the dc voltage at the output of the rest of this grade is well above the potential of land and therefore the level converter is used to reset this to zero voltage relative to ground.
Non-inverting input
Inverting input
Diff Diff Amplifier Amplifier Attaché emitter push-pull amplifier input dual-input dual-generator constant output with additional symmetrical asymmetry output power symmetry
Figure 4.1. Block diagram of a typical TE
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All these steps are made in mikropoiimeni structure with several transistors, and the TE in the form of a microchip (chip) with various akrolipsies or terminals respectively leading to "feet".
Figure 4.2. Image display and an equivalent circuit of the operational amplifier MC1435
4.2 Notation - Ideal Operational Amplifier
The symbol depicts Sch.4.3 a TE, which has two inputs and one output. Figure does not show the terminals of the voltage nor the other terminals. As the first step of the differential amplifier is TE, the differential inputs is denoted by a (+)
and the other with the (-). The (+) input is non-inverting input. If the entrance is an applied ac signal (or a dc voltage), the output displays an amplified signal having the same phase (same polarity) with the input voltage. But if the same signal is applied to the input (-), so the output signal appears Exit enhanced with phase difference 180 ° (opposite polarity) to the entrance.
You're inverting. U2
You're not inverting. Ui
Figure 4.3. Schematic symbol of the TE
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Where:
Y1 = the voltage at the non-inverting input Y2 = the voltage at inverting input y0 = the output voltage
(All these trends are measured on earth).
A0 = differential reinforcement of large signals TE, which is determined by the manufacturer.
O is an ideal TE (idealized) theoretical model of the TE
following characteristics:
1. Infinite differential reinforcement A0.
2. Infinite input resistance R:, in order to strengthen any signal normally, with no trouble adjusting to the upstream.
3. Zero output impedance R0, so the output can drive without any trouble adjusting next level.
4. Zero output voltage for zero input voltage.
5. Infinite range of transit frequency that enhances any signal frequency from 0 to ¥ Hz without degradation.
6. Infinite mode common reason, that the noise output voltage common mode is zero.
7. Infinite tilt rate (slew rate), so the change of the output voltage to be made simultaneously by changing the input voltage.
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But there are practical TE can reach quite all the features of the ideal TE using negative anasyzefxi. In particular, the input impedance, and output frequency range can pass much closer to these ideal values.
The Sch.4.4 shows the simple equivalent circuit of a real TE. The circuit includes important information from the manufacturer's data: A0, Ri and R0. The A0 uid is the equivalent Thevenin voltage source and R0 is the corresponding equivalent resistance seen at the output of the TE.
You're inverting.
You're not inverting.
Figure 4.4. Equivalent circuit TE
4.2.1 Effective Operational amplifier
In practice, real operational amplifiers approaching approximately characteristics applicable to the ideal TE. So are large (instead of <*>)
differential reinforcement A0 high (but not ¥), high input impedance Ri (but not ¥ output resistance, R0 small (but not 0) frequency range transit BW small (but not <*>). So the output voltage is given by:
U = A0Uid = A0 (u2-u,) (4.2.1)
where A0 = aid differential voltage or open-loop gain uid = differential input voltage
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Analogue Electronics
U = the voltage of the non-inverting input to ground as u2 = the inverting input voltage relative to ground This equation shows that the output voltage is proportional to u0 (algebraic) difference of two input voltages. That is, HE strengthens the difference between the two input voltages and not the same these trends. For this reason the polarity of the output voltage depends on the polarity of the differential input voltage.
Non-inverting amplifier 4.3
Support open loop A0 real TE is too great. For this reason, very small signals (in the order of memory or less) with low frequency may be supported comfortably without distortion. But the signals are very susceptible to noise.
Besides, strengthening open loop voltage of TE is not constant but varies with temperature and supply voltage due to the high volume of TE by the manufacturers.
Furthermore, the transit frequency range (ie the band of frequencies for which the aid is kept constant) for most TE is almost negligible (very small). For this reason the practical TE an open loop applications not using ac. Eg crossing the range 741C is about 5 Hz, which means that this TE is not useful for virtually any practical application.
For the above reasons is usually applied to the TE anasyzefxi negative, so it can be used in practical applications ac. The Sch.4.5 shows with TE
connections and non-inverting anasyzefxi.
Figure 4.5. Non-inverting amplifier with TE
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Then proves that the relations are:
(4.3.2)
(4.3.3)
(4-3.4)
where Af = the closed loop voltage support
Rif = total input impedance of the amplifier anasyzefxi R0f = the total output impedance of the amplifier anasyzefxi
and b = the percentage or rate anasyzefxis, which is equal to
(43.5)
4.3.1 Frequency Range Crossing with Anasyzefxi
The transit frequency range (BW) of an amplifier, defined as the area (region) frequencies on which it remains constant. Manufacturers generally specify the product or support transit or x range gives the response curve of the open loop A0 aid in the frequency f. The Sch.4.6 shows the dependence of the open-loop payment in frequency for the TE 741C. From this curve it appears that the aid (A0) is 200 000 (106 dB) and crossing the range of about 5 Hz, thus enhancing the product range crossing x is 1 MHz (200 000 x 5 Hz).
At the other end of the curve is the support 1 and frequency 1 MHz, so the range is again crossing 1 MHz. Therefore, strengthening the product range crossing x is stable. For the TE 741, the cutoff frequency f1, the support is A0 is 3 dB below its value at 0 Hz is equal to 5 Hz. It turns out that the cutoff frequency is given by:
f1f = (1 + b A0) f
(4.3.6)
Figure 4.6. The frequency-response curve for the TE 741
This equation shows that the range of non-crossing - inverted amplifier and TE anasyzefxi increase multiplied by the factor (1 + b A0).
Example 4-1
The circuit non-inverted amplifier has Sch.4.5 KO R1 = 4.7 and R2 = 12 KO Find the total voltage gain of the amplifier, the input impedance, the output impedance and range of passing. Emphasis is on 741, R = 2 MO R0 = 75 and Z
We have:
Solution
4.4 Amplifier with reversal
The Sch.4.7 shows the circuit (closed loop) TE-syndesmolo
gimenos as inverting amplifier. This circuit creates different-
hour 180 ° phase between the signal input and output, so
reverses the polarity of the input voltage. It turns out that
, the following relations:
R2
WW
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So
Figure 4.7. TE wiring as inverting amplifier
(4.4.8)
(4.4.9)
(4.4.10)
(4.4.11)
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Example 4-2
O Sch.4.7 amplifier consists of a TE 741, with R, = 1 KO and R2 = 10 KO. Calculate the amplification, input impedance, the output impedance and frequency range of the crossing.
They are:
So
Solution
