comparator, why public way, rate gradient compensation.
pp 100-110
4.10 Coordinating amplifier
O coordination of which amplifier is an amplifier that can be tuned, so to have maximum benefit, at some frequency and consists of a parallel LC network coordination combined with a TE as in Sch.4.16. At the same shape and the curve depicts the frequency-response.
Figure 4.16. Coordinating amplifier
The resonant frequency <peak frequency to the peak (maximum) frequency response curve, determined by the combination of L and C and is given by
The inductor L at the resonance frequency o0 = 2pi0, characterized by a quality factor Q = o0L / r, where r is the ohmic resistance. To accurately apply Eq. (04/10/28) should Q> 10.
The impedance of the parallel circuit increases as we approach the coordination and becomes maximum at the resonance frequency. Therefore, the support (voltage gain) of the amplifier in the coordination will also be given a maximum by the relation:
(4.10.29)
where, Rd the equivalent dynamic resistance of the parallel circuit, which is:
RD = QV (4.10.30)
The range of transit Resonant frequency amplifier is by:
(4.10.31)
where QD is the so-called dynamic Q parallel resonant circuit LC, which is
(4.10.32)
Example 4-7
The circuit has Sch.4.16 support 10 and the resonance frequency of 16 kHz. Find the values of the remaining elements of if, C = 0.01 MP, r = 30 O, R1 = 1 KO.
Solution
In principle, we use Eq. (4/10/28) and calculate the L:
L = 10mH
O Q factor of the coil is:
and
Finally, we calculate the R2 using Eq. (10/04/29), which gives
102 Analogue Electronics
R2 / / Rd = R1 X A, = 1000 X 10 = 104
Therefore,
R2 10 KO
4.11 comparator
Sometimes it is necessary to compare two trends to determine what is the biggest one to determine the threshold function. An example is the electronic thermostat that turns the temperature trend. When the voltage corresponding to the room temperature is the lowest voltage setpoint corresponds to a post-threshold of the thermostat, the system generates a difference signal activates the kallorifer.
The complex case is the saturation comparator, which is a differential amplifier with IS and shown in Sch.4.17. When the input voltage u is greater than the reference voltage Vn (u> Vn) the output voltage is positive, while for u <to, the output voltage is negative. Because as you know, TE has been a great aid output is driven immediately to the gross registered tonnage.
Thus, the output voltage takes the positive saturation value, equal to a supply voltage + VCC, or negative saturation value equal to the other voltage-Vcc, depending on whether u> to or u <Vn, Sch.4.17 B. The mapping can be operated and vice versa
Sch.4.17g, d.Vcc
Operational AMPLIFIERS
103
(B) (d)
Figure 4.17. Saturation comparator with TE
When the input is changed by passing the reference voltage Va, the output generated by a transition to a value / state to another, when the input voltage u passes through the axis of the trend. That is, the one time the input voltage can be lower than the reference voltage, and the next moment the opposite is true. Ideally, the output would change instantly from a positive value of the saturation voltage, V + = Vcc, the negative value of V_ = - Vcc. In practice, however, always require a little time to change the TE position. O time is called response time tr and is due to the phenomena parasitikis capacity of the circuit. Typical value of this response time is just m $. Eg. in the TE 741 years is about $ 40 m.
In order to achieve specific performance, specially constructed comparators.
Such is the comparator 710 is specially designed for TE have a very short response time is less than 40 ns and operates with supply voltages of +12 V and -6 V. The output switches between +3.2 V and -0.6 V, so that it can work with logical systems TTL and DTL.
Sometimes, there may be in trouble comparators called "shaking"
is particularly important if the input signal is quite noisy. In this case instead of having a direct and simple transition from one state to another, when u tends to pass, you may see a rapid oscillation from one state to another. This phenomenon is avoided if we create a lag in SCD characteristic of the comparator.
These are understood to Sch.4.18 shows the comparator with hysteresis 710
50 mV. As observed in the non-inverting input of the differential amplifier is applied through positive anasyzefxi of which is determined exactly epiferomeni lag. When the output of the comparator changes state, the effect of positive anasyzefxis causes a change in voltage reference, such as having a relatively large change in the input signal to reverse the output state. Thus, the amplitude of any fluctuations of the input voltage is not sufficient to manifest the oscillations "shaking".
Figure 4.18. Comparator hysteresis
The hysteresis of the comparator is given by:
Dn0 where is the difference between the two states of the output voltage, ie n = Dn0 + - V.
Substituting the numerical values of the circuit, it follows:
DN = e.jr20. 3.8 V 50mV
0.220 + 15
Operational AMPLIFIERS 105
4.12 ratio of common mode
Normally the TE is used to enhance the difference between the two input signals of the. Therefore, it works with the differential manner. You should therefore enhance the signals, eg noise voltages that occur simultaneously in both input and therefore do not appear to exit.
The circuit of Sch.4.19 shows the two entrances of the TE connected together and stimulated by the common brand ucm. This method of connection is called "common mode".
Ideally, the corresponding output will be zero. But in practice this does not happen. O ratio of common mode output voltage, a true TE, corresponding to the input voltage is the voltage common mode support, Acm = u0 / ucm .. To qualify how much approaching a real TE behavior of an ideal TE mode in terms of how common the ratio of common mode (Common Mode Rejection Ratio), defined as the ratio of aid dc open-loop, A0, to enhance public way ie
(4.12.34)
(4.12.35)
Typical values of CMRR is 80 to 100 dB.
The higher the ratio the more ideal CMRR is the TE.
With appropriate kyklomatosi be greatly increased ratio CMRR. Such is the case of the differential amplifier Sch.4.10,
where the ratio of common mode is expected to be infinite. In practice, however, because the resistors have a tolerance to their values, the CMRR is infinite, but simply great.
106 Analogue Electronics
Figure 4.19. TE syndesmologimenos as common mode
4.13 Rate slope
Because the practical TE has a frequency response that depends on the frequency, output voltage is stepwise when the entrance is stepwise, Sch.4.20. This is due to the small internal capacity of TE.
O gradient rate (Slew Rate, SR) is defined by the above figure, are:
(4.13.36)
It turns out that the maximum frequency with which it works well, the TE is given by:
f = SR
Tmax 2 pi x K x U
(4.13.37)
Solution
Operational AMPLIFIERS
107
where
SR = is the rate of slope is
K = is the strengthening of the amplifier
U = the input voltage peak to peak (pp).
Example 4-8
O 741 is SR = 0.5 V / m $ and excited by input voltage of 1 V and
support is 5. Find the maximum frequency that can work
TE correctly.
4.14 Hedges in TE
The operational amplifiers are not ideal and for this reason, when we use a dc applications must take some additional steps on ¬, as we shall see immediately below.
4.14.1 Input Voltage Compensation
The output voltage of an ideal operational amplifier should be zero, when the two entrances, the (-) and (+), the signal is zero, ie for zero input voltage to have an output voltage of 0. But in practice, not just so the deviation from zero is called the compensation voltage output. Basically this is due to the lack of symmetry of the input stage of the TE. For this reason we must take care to restore zero output voltage for zero input voltages.
At the manufacturer's data is reported as the TE input voltage compensation
Voffxt or Vos and the voltage to be applied in one of the entrances or any other designated points of the TE, in order to restore zero output voltage for zero input signal. The Sch.4.21 shows the voltage compensation is represented by a voltage on input (-) short-circuited by the input voltages. The output voltage due to voltage compensation (offset), Sch.4.21 are:
(4.14.38)
This relationship applies whether the amplifier is connected as an inverter or not and gives the output voltage to compensate the input voltage compensation by the manufacturer.
Figure 4.21. TE input voltage compensation
The input voltage compensation are some mV. Because the amplifier makes strengthening (strengthening of the closed loop) shows the voltage at the output of this enhanced TE. This trend changed in amplitude and sign (- or +) from one amplifier to another, the same type TE. Also, the width of the input voltage compensation is subject to slippage, which is a function of temperature, time and supply voltage.
The maximum input voltage to compensate for the cheap mA709 TE, and mA740 mA741 is 7.5 mV, 100 mV and 6 mV, respectively.
Example 4-9
If the resistance of an amplifier without inversion is R1 = 1 KO and KO R2 = 100 to
Find the output voltage compensation, if the TE is 741.
10 K
Operational AMPLIFIERS
109
Solution
6 mV = 606mV 0.61 V
It is obvious that without the offset voltage compensation will have a serious problem in the output. The Sch.4.22 shows how we compensate for the TE. The positive and negative voltage potentiometer corrects the voltage compensation is either negative or positive.
R2
O TE 741 has two special terminals (the terminals 1 and 5) offset voltage and offset gets in the way that shows Sch.4.23, ie by adjusting the potentiometer until the input voltage become zero for zero input voltages.
Vcc
The
Vcc
Figure 4.23. Offset voltage of the TE 741
To be the trend esodou 0 turns out, that should apply
the relationship:
R 1R 23 Ri + R2
In this case the output voltage becomes:
Vo = (I2-Il) R = UA
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4.14.2 Input Polarization Compensation & Stream Input
All practical TE have another limitation should on both entrances to enter a steady stream, to be given the right conditions of internal polarization components of the amplifier. This stream should not be confused with any signal power that may be entering the terminals of the amplifier.
The currents I1 and I2 polarization depicted in Sch.4.24 and enter the two inputs of the amplifier. The difference I1 I2-called current compensation Ioffset.
Effect of bias current trend is to have at the output voltage V0. This trend has two components and is given by:
(4.14.39)
Figure 4.24. Input bias currents and bias
(4.14.40)
(4.14.41)
The typical values of compensation currents of the TE 709, 740 and 741 are respectively 100
nA, 60 pA and 20 nA, respectively.
