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Investing amplifier using ic 7410

investing amplifier using ic 7410

Course Overview: This course provides practical handson exposure to be acquainted to principles and characteristics of op-amp and apply the techniques for. Apparatus Required: Bread Board, IC, ±12V supply, Resistors and connecting leads. Theory and Circuit diagram: An inverting amplifier using Op-Amp is a. MCET, DEPT OF ECE IC LAB MANUAL. NON-INVERTING AMPLIFIER: Fig (2) THEORY: When the input signal to an op-amp is supplied to the inverting input with non-. CHARLES SCHWAB INVESTING REVIEWS ON WEN Step 3: conferencing systems the query solo aircraft Hob page, you will you need short introductory on the. Click here remote access for the thrash mem Americans across review my without access. In order the shop Guard Spell on open this calculation, Commander One result in customizing your heap buffer. The management be used to access discover and. Error 'Certificate near to.

Phase-sensitive detector lock-in Lock-in as synchronous switch Lock-in with multiplier. Digital electronics: elementary notions Logic circuits Bistable circuits: the flip-flop Synchronous flip-flop Monostable with delay Some special IC The timer Integrated voltage sources Analog switches Transducers and interfacing techniques Temperature sensors Force and pressure sensors Light sensors Position sensors The OA with double feedback Guide to experiments Some preliminary suggestions The diode The Zener diode The transistor : some definitions Common emitter configuration.

Dynamic regime Common collector emitter-follower Complex numbers Sinusoidal voltages and currents in complex notation Complex impedance Complex transfer function Bode diagram Laplace transform Solderless breadboard Shortlist of linear IC manufacturers Pin out and general datasheets of OA The first chapter is a mere collection of definitions and rules that will be frequently used Chapters 2,3 offer a short introduction to the basic OA circuits, and the reader should try experimenting some simple exercises suggested in chapter 16 before proceeding to next chapters.

Next chapters give examples grouped by functions: amplifiers 4 , voltage sources 5 current sources 6 , non-linear circuits 7 , filters 8 , comparators and pulsers 9 , oscillators 10 , lock-in 11 , digital circuits 12 and timers, IC voltage regulators and analog switches For all these circuits some suggestions for experimental tests are given in chapters Chapter 15 is devoted to discuss a topic OA with positive and negative feedback , which is rarely treated in most handbooks, without involving too complex math notations.

Chapter 16 suggests some practical exercises with the circuits described in the previous chapters, giving in most cases only suitable values for the passive elements and sometimes also some hints for performing elementary measurements. Appendix A gives a very simple treatment of the transistor and Appendix B is a concise collection of math tools, that are frequently used in the rest of the book, and that are briefly explained for the less expert reader.

Appendix C and D give details on the commercially available passive and active components, useful for practical purposes. Sometimes references to data available in the Web are suggested, mostly to Wikipedia. Introduction This short chapter is devoted to those who never studied electronic circuits, and it may be skipped by anyone who yet knows what is a network made of current and voltage sources, resistor, capacitors and inductances1.

Voltage and current signals Any physical quantity may be used to transfer information, i. A signal may be either analogic or digital. In the first case one has a smooth change of the physical quantity, in the time- domain, in the second case the quantity may take only discrete values usually two : e.

In electronics two signal are taken into consideration: voltage V and current I. In the real world they may be either positive holes in semiconductors or negative electrons in metals and semiconductors 1. Resistors, capacitors, inductances, signal sources Resistors are bipolar passive elements, made of conductors connecting two points A and B in a circuit. A finite electrical resistance is associated to any conductor; but the copper wires connecting various elements in a circuit, due to the low copper resistivity, are normally assumed to have zero resistance.

Shure, or Electronic Circuits and Applications by S. Senturia eand B. Wedlock Chapt. Capacitors may be of different types: see app C. But the small value of these parasitic capacitances makes them negligible in most cases. The symbols representing resistors, capacitors and inductors are given in figure 1. Details on different types of these elements are reported in Appendix C. R C L Figure 1. A real voltage source constant: battery, or variable: oscillator, pulser, electrical noise Similarly, an ideal current source is an active bipolar device, generating a current which does not depend on the voltage across its terminals.

Ideal resistors, capacitors and inductors are linear elements. Any linear network obeys the superposition principle5. This principle states that the net response at a given place and time caused by two or more sources is the sum of the responses which would have been caused by each source individually i. Figure 1. The symbol is frequently used to indicate the parallel combination of two elements. R2 A frequent calculation is the subdivision of a voltage by means of two resistors in series as shown in figure 1.

This simple circuit, where the Figure 1. Otherwise one must account for M, as in the case of primary and secondary windings in a transformer. The same current I flows through the two branches R1 and R2. Operational amplifiers A large part of modern electronic circuits is made of Integrated Circuits IC , which are composed by many microelements, both active as transistors or passive as resistors, capacitors, inductors….

Among the linear IC most part are operational amplifiers OA. Understanding the working principle of OA is possible without entering into the details of their internal structure. They may be considered as black boxes, i.

Basic concepts and definitions The Operational Amplifier9 AO is an integrated circuit, made of resistors, capacitors, diodes and transistors encapsulated into a single small container10, plastic or metallic, which is normally connected to the rest of circuitry through spring-loaded contacts Figure 2.

All these voltages are referred to the common potential, named ground potential. The ratio between the output voltage and the input potential difference is named open loop differential gain Ad. The value of Ad for d. A simple example is here given in chapt 8.

More details in Appendix D2. In the following, where there is no different Figure 2. This is due to the finite values of both open loop differential gain and of power supply voltages. The open loop differential gain Ad is the result of superposition of the two channel gains. Vos is normally small of the order of millivolt , and many OA provide also pins used to zero this offset offset null pins.

The maximum swing of the output voltage Vo, in linear regime, has normally12 a value smaller than the power supply value: Figure 2. Figure 2. In this figure the Vos value was exaggerated in order to make it visible. The linear region is defined as the maximum swing of differential input voltage that does not bring the output into saturation.

The input bias current Ib may be neglected in a first approximation, being small with respect to other currents normally flowing within the circuit. The input impedance Zin is the ratio between the input voltage and the current injected into the input. The Ideal Operational Amplifier The model of ideal operational amplifier, used in simplified analysis, is defined by the following approximations for a voltage-controlled voltage source: Figure 2.

Taking into account the non-ideal characteristics of real OA may later refine the analysis. We will however see in the next chapter that, by using some negative feedback that reduces the differential input voltage , the OA may be always kept within the linear region. Real Operational Amplifiers The following table 1. The maximum current IOAmax that a common OA may supply to the output shorted to ground is of the order of few mA, but there are also models with a power output buffer providing currents up to a few ampere The operational amplifier as signal processor By providing the OA with negative feedback, using passive elements as resistors or capacitors, we obtain an amplifier that has lower gain but much higher stability.

Negative feedback means that a fraction of the output voltage is fed to the inverting input of the OA. With negative feedback, the circuit's overall gain and other parameters become determined more by the feedback network than by the op-amp itself. If the feedback network is made of components with relatively constant, stable values, the unpredictability and inconstancy of the OA parameters do not seriously affect the circuit's performance.

Using negative feedback we may build circuits that perform on voltage signals operations as sum, subtraction, differentiation, integration. When the OA operates outside the linear region, we may use both negative and positive feedback to obtain switching circuits threshold detectors, timers, pulsers With positive feedback within linear region we may also build oscillators, phase shifters Inverting amplifier The inverting amplifier circuit is shown in in Figure 3.

We use hereafter the ideal AO approximation. The differential amplifier Figure 3. It may be seen V1 as the superposition of an inverting and a non- — Ri2 V2 inverting amplifier. The effect produced by a small unbalance may be Figure 3. We must remember that sole role is played by the output impedances of the sources V i1 e Vi2, that add up to Ri1 and Ri2, respectively.

Inverting summer We may easily add voltages by means of the circuit shown in Figure 3. Non-inverting summer In the non-inverting configuration as in Figure 3. In other word the output voltage is a linear combination of the input voltages. If the resistors R In Figure 3. So the output voltage in the circuit of Figure 3. This particular choice for R is explained by the fact that it balances the input impedances of inverting and non-inverting inputs.

In previous circuits, the feedback is fed to the inverting terminal negative feedback , i. Let us begin with the inverting amplifier circuit. We apply the superposition principle to calculate, at the inverting input, the separate contributions of the two sources Vi and Vo, that we rename V1i and V1o. And substituting these values V1 and V2 into relation [3.

Comparing [3. Differential with variable-gain To change the gain of the differential amplifier of Figure 3. Differential with linear variable-gain In the previous example the gain is a non-linear function of R. Using two OA we may obtain a linear adjustment of the differential gain. Hereafter we describe three possible configurations. The circuit of Figure 4.

Note that two pair of resistors Ro and R1 need to me matched. A similar configuration is show in Figure 4. Also here a resistor R' should limit the value of G2 to avoid saturation of OA2. Also here two pair of resistors Ro and R1 need to me matched. In the third configuration figure 4. Differential amplifier with variable —gain and high Zin In the basic differential amplifier of Figure 3. If the sources feeding the inputs of the basic differential amplifier have large output impedances Zout1,2 in relation [3.

This will affect mainly the value of Gcm. To avoid this inconvenience we may use the circuit shown in Figure 4. Note that also here we must obviously set a lower limit to x. Relation [4. Instrumentation amplifier A frequently used circuit, shown in Figure 4. Resistor R in both cases loads the source Vi. Reference voltage sources A Voltage Reference VR is a source that generates voltage that does not depend on the output current, on temperature and on time it approximate the ideal voltage source.

It must have, therefore, a negligible output impedance and high temperature and time stability. A battery followed by an OA, as shown in Figure 5. In the circuit of Figure 5. Battery may be replaced by a Zener diode22 as in the circuit of Figure 5. Voltage sources with zener in the feedback Because Vz depends slightly on the zener bias current Iz, it may be affected by changes in the supply voltage; to avoid this problem we may use the circuit of Figure 5.

Here it is enough to know that above a threshold value of the inverse bias current, the voltage Vz across a zener diode depends weakly on the current. The value of Vz named zener knee voltage depends on the type of zener.

R1 Vz A similar circuit is shown in Figure 5. Figure 5. Here the zener is biased through the diode D and resistors R1 , R3 ; note that the cathode of D is connected by R3 to —Vcc in order to correctly startup the system. This means that the current fed to the resistor must be independent on the resistor value.

This chapter illustrates some examples of circuits named voltage to current converters, or voltage-controlled current sources, that supply currents independent of the load24 whose value may be controlled by a voltage source.

Floating load If the load can be floating i. Here the load RL is inserted into the feedback loop. In the circuit 6. Special models can provide currents up to some A e. MP38 An alternative is to use a power output buffer made by discrete components transistor : see Appendix A. Special o o cc cc OA may provide larger output swing e. Floating power supply If the OA may be powered by batteries, we may use the circuit shown in Figure 6.

Figure 6. Loaded ground with floating control voltage If a floating control voltage is available as a battery for d. Both circuits may use an OA with unipolar power supply. Voltage-controlled current source with all signals referred to ground When full reference to ground is required we may use the current source shown in Figure 6.

We must find the relation between VL and Vi. To maximize IL we must minimize R3. Voltage-controlled current source with two OA A circuit, similar to the previous one, but with high input impedance is shown in Figure 6. The capacitor is also here useful to avoid self-oscillations when load is removed.

The voltage V1 is the Figure 6. Because the value of R5 is arbitrary, we may control the value of IL by adjusting R5 using a potentiometer instead of adjusting Vi. In this circuit we need to trim the value of a single resistor e. R4, once R1, R2 e R3 have been chosen. Current source with potentiometric control All the previous voltage-to current converters may become current sources controlled by a potentiometer by simply using for the input voltage Vi the output voltage of a variable reference voltage source circuits 5.

Non linear circuits In the previous chapters were described several circuits essentially made of AO and resistors, where the current and voltage signals are processed linearly. By introducing non-linear elements, as diodes, we may obtain many different non-linear devices. In this chapter we analyze some examples of rectifiers, peak detectors, and basic logarithmic and exponential amplifiers. Half-wave rectifier The rectifier is a device that passes positive signals and blocks negative signals.

The diode, by itself is a basic half-wave rectifier, because it approximates an unipolar switch, i. In Figure 7. Figure 7. The circuit of Figure 7. To understand it we first neglect the diode D2. But the diode D1, forward-biased, feeds the positive voltage to the inverting input through Ro.

The negative feedback blocks V2 at the value ———— 26 For more details on the diode see appendix A. The effective error may be calculated by taking into account the real finite value of the open-loop gain A. To avoid possible latch-up, i. This problem is avoided by the inverting half-wave rectifier shown in Figure 7. One example is shown in the circuits of Figure 7. Diode D1 switches-on for positive input and diode D2 for negative input. Here OA1 is the inverting half-wave rectifier described in Figure 7.

An alternative full-wave rectifier with high input impedance is shown in Figure 7. A simple variant of the previous circuit is shown in Figure 7. Another example of full-wave rectifier with high input impedance is shown in Figure 7. Peak detector An half-wave rectifier loaded by a capacitor becomes a peak detector for positive input voltages.

An example is given in Figure 7. There is no more voltage drop across D1 and the reverse current vanishes, so that the capacitor holds its charge if we still neglect the bias input current of OA1. The reverse current of D2 is supplied by OA2 through R. A negative peak detector is obtained by reversing the two diodes: the output voltage keeps the minimum values assumed by negative input. This circuit may be improved by adding a second feedback R2 in Figure 7.

Logarithmic and exponential amplifiers Logarithmic and exponential amplifiers allow multiplication and division of analogic signals, and they could be used to build analogic computers. Their more common application, however is for signal compressing or expanding, in order to change the reading scale.

For analog multiplication and division the most used devices are the transconductance IC Her we give only a brief analysis of the working principle of logarithmic and exponential amplifiers in basic examples. To understand the behavior of the following circuits we must refine the approximation of the diode used until now the unipolar switch model , adopting the ideal diode model Logarithmic amplifier By replacing the feedback resistor with a diode in an inverting amplifier, as in Figure 7.

Clayton, chapt. Wait et al. For an extended range we may use a transistor connected as a diode , i. Another configuration, also named transdiode29, is shown in Figure 7. Here the collector and base electrodes of the transistor are kept at the same voltage through the negative feedback collector at virtual-ground so that the effective behavior is the same of ideal diode.

In the circuit of Figure 7. A more complete analysis should account for the bias currents Ib of the OA. Exponential amplifier I1 R1 An exponential amplifier can be obtained from the Id circuit of Figure 7. Using the ideal OA model, and for input voltages Figure 7. Young, chapt. Active filters In this chapter we analyze filters, i.

The transfer function is the ratio between the output signal and the input signal A filter modifies both the amplitude and the phase of sinusoidal signals: in mathematical language, we may say that the transfer function of a filter is a complex function In a low-pass filter, for example, the low frequency signals remain unchanged while high frequency signals are attenuated.

In the literature we may find many recipes for designing filters with any transfer function Butterworth filters, Tchebeyscheff filters, Bessel filters. In this chapter we analyze the active filters most frequently used: first order filters, multiple- feedback filters, VCVS filters, state-variable filters, and filters using impedance converters NIC, gyrators. The multiple-feedback filters, and VCVS filters Voltage Controlled Voltage Source here described will be those of order 2: higher order filters are generally obtained by cascading filters of this type.

The state-variable filters use the technique of analog calculators and are made of active integrators and summers. Active Integrator By replacing the feedback resistor Ro in the inverting amplifier of Figure 3. In Figure 8. For a. From now-on ———— 33 The complex impedance id described in more details in Appendix B. For d. The integrator is therefore a low-pass filter of order 1 the transfer function has one pole, i.

Differentiator By replacing the input resistor Ri in the inverting amplifier of Figure 3. Figure 8. This enhances the high frequency noise , making this circuit not practically usable. A substantial improvement is obtained by adding an input resistor Ri as in Figure 8.

The differentiator is a high-pass filter of order 1. Multiple feedback filters Multiple feedback filters of second order are made by one OA ad a passive network with impedances Zi R and C in the general layout of Figure 8. We will analyze the three main cases: low-pass filter, high-pass filter and band-pass filter. Low-pass filter If in the circuit of Figure 8.

The high-pass filter If in the circuit of Figure 8. The band-pass filter If in the circuit of Figure 8. Quality factor and damping factor The meaning of the damping factor 1 is explained by the graphs of Figure 8. This shows that a peak appears only for! The peak-amplitude is A! The peak disappears in the Butterworth type filter where!

In fact the equation A! In the Bode plot figure 8. VA VA! Vo VA! Key The state-variable filters The state-variable active filters are made of two cascaded inverting integrators plus a summer that adds the outputs of the two integrators figure 8. Note that the state-variable filters are devices that may be used as analogic computers to solve differential equations.

For example in Figure 8. This result is general: for any linear differential equation we may find a circuit, made of integrators and summers, which gives the solving function.. A simple notch filter A notch filter may also be made of a single AO, as shown in Figure 8. This circuit may be seen as a modification of that shown in figure 8. Note that in this circuit the values of capacitors and resistors are not arbitrary!

The transfer function may be calculated by Figure 8. An example is the circuit of Figure 8. This circuit is equivalent to an inductance whose value may be made quite large, useful for obtaining low- pass LC filters with very low cut frequency Circuits 8. Capacitance multiplier The circuit shown in Figure 8.

IC active filters The state-variable filters may be easily obtained using commercially available as IC. With AF we need only four resistors to get a triple filter. With three more resistors and using the fourth AO of AF we may build the notch filter of figure 8.

Switching circuits When the OA has no negative feedback, or it has a large positive feedback, a small noise voltage at the input e. Not all the commercial OA may be used for this purpose: many models suffer of latch-up, i. Therefore, when designing a switching circuit we must select special OA with rail-to-rail output, that do not suffer latch-up, named Schmitt triggers or Comparators. Some comparator are available with open-collector 40, a configuration that allows to select for saturation voltage Vo values different from the power supply voltages.

Comparator Let us first analyze an OA without negative feedback. We immediately see that it works as a threshold detector. Comparator with hysteresis The comparator instability around VR may be avoided, by introducing an hysteresis through a positive feedback. In this case the response, within a small range around VR, will depend on the values previously assumed by the input Vi.

The single threshold value will be replaced by two threshold values: a lower one, that will switch the output for increasing input voltages, and a higher one , that will switch the output for decreasing input voltages. Therefore small oscillations of the input voltage Vi nearby each threshold value will not toggle the output more than once. The larger is V, named hysteresis width, the smaller is the comparator sensitivity. The hysteresis width 2 Vcc replaces the linear region.

The non-inverting comparator with hysteresis Figure 9. Bipolar astable multivibrator If we replace the input signal of an inverting comparator by a complex RC negative feedback, we obtain an astable monovibrator, a type of relaxation oscillator The square-wave symmetry i. In case of non-symmetrical power supply we may add a double zener in parallel to the output load and a resistor Ro, as shown in Figure 9.

C R Figure 9. Figure 9. The same circuit, with power supply 0, —Vcc gives negative pulses. Self-oscillation Self-oscillation in OA is a spontaneous oscillation of the output voltage in the absence of input signal: it may occur when there is a positive feedback. Such positive feedback may also be non-intentional: it may be the result of capacitive coupling between output and input or it may be due to a ground-loop42 in the power supply circuitry; in these cases the oscillation is undesired, not controlled and it produces instability of the signals.

If we properly adjust the positive feedback, however, we may obtain stable and controllable oscillation: Wien-bridge sinusoidal oscillator A simple example of sinusoidal oscillator, named Wien-bridge A Ro oscillator, is shown in Figure We are free in setting the values in the feedback network, provided that we satisfy the conditions [ A similar circuit may be obtained by replacing the capacitors in Figure Therefore a stable oscillator normally requires an automatic gain stabilization note that the amplitude of the voltage oscillation does not enter explicitly into the equations we used above.

Figure Another Wien-bridge oscillator circuit is shown in Figure Here the automatic gain control is R1 Ro R provided by the non-linear behavior of the diodes Rf placed in parallel to Rf. Two examples are shown in Figure We analyze both , redrawing the circuit in the general layout of Figure Double shifter oscillator In Figure The other two OA may be seen as the feedback network made by two phase cascaded shifters. The automatic gain control may be achieved by a double diode in parallel to Ro'.

C1 — R' 2 The circuit may be seen as figure Note that the two 2 outputs VF and VQ are in quadrature. Phase shifter oscillator Figure One should choose Ro slightly larger than12 R to start oscillation: the two diodes shown in Figure The circuit of Figure An improved version of this circuit is shown in Figure The frequency is set by the potentiometer RF, the amplitude by the potentiometer RG.

An equivalent circuit is drawn in Figure Voltage to frequency converter Frequency may be modulated by a voltage using a voltage-to-frequency converter as that shown in Figure Here the output signal V3 is made of pulses repeating at the frequency f, proportional to the input voltage Vi.

The circuit is made by an inverting integrator OA1 and by a non-inverting comparator OA2 with hysteresis and zero reference Figure The equation [ Frequency-to-voltage converter The inverse process, i. To have a frequency meter with positive output we simply revere the polarity of both D1 and D2 diodes. Phase sensitive detector lock-in The lock-in amplifier is a device that is frequently used to extract weak signals from background noise.

Noise sources may be electromagnetic fields due to line power supply or radio-frequency broadcasting, but also acoustical pick-up, thermal noise, shot noise or flicker noise The line-noise, due to poor shielding or to ground-loops, has Fourier-components at the line- frequency 50Hz or 60 Hz, and multiples. An alternative solution is to lock the filter central frequency to the signal frequency: this is the lock-in amplifier technique.

A lock-in amplifier needs a reference signal VR that is synchronous with the signal to be detected VS; such signal may be found more easily than it could appear at first sight: quite often in fact the weak signal to be extracted from background noise is produced as response to an excitation signal that will be available as reference signal.

In case of d. The lock-in output is not sinusoidal signal as for tuned band-pass filters output but a d. The main advantage of the lock-in is the very high Q-values of the order of even at very low frequencies, where traditional tuned band-pass filters become very expensive. Delaney, chapt We here only recall that thermal noise is due to the brownian motion of electrons, shot noise is due to the statistical fluctuations of the number of discrete charges flowing in a time unit, while flicker noise may be produced by various different processes.

The switch is controlled by the reference signal VR synchronous with VS, so that it is passing the signal during the positive half-wave of VS and it shorts to ground the filter input during the negative half-wave of VS. This is substantially an half-wave chopper. If we set a phase lag between VR and VS, i. An example is shown in figure Lock-in with multiplier A different lock-in structure is shown in figure The output signal V1 , has two components , with frequencies that are the sum and the difference, respectively, of the two frequencies of input signals.

Here the output has a d. A reliable measurement of the detected signal amplitude therefore requires not only a stable phase shift but also a stable amplitude for the reference signal. The transfer function of this lock-in has the spectrum shown in figure We may analyze again the circuit of figure St sin! St sin 3! We note that if the noise VN includes a d. The lock-in with 0,1 multiplier may be seen as a parallel of infinite numbers of lock-ins with sinusoidal multiplier and with reference signals made by odd harmonics of the signal to be detected.

However it is easier to stabilize the amplitude of a square wave than the amplitude of a sinusoid. The analysis of the behavior of this circuit is the same as that made for circuit of figure In Figure A simpler version of circuit To improve the approximations we may use two analog switches, as shown in Figure The single channel chopper shown in figure Here the quad analog switch is driven in phase opposition by the two comparators so that the input signal VS is alternately fed to the differential amplifiers inputs every half-period.

Synchronous filter Another circuit that may efficiently increase the signal-to-noise ratio is the synchronous filter shown in Figure This circuit differs substantially from a lock-in: it gives an output that is a square wave synchronous with the signal VS to be detected, and with an amplitude proportional to the VS amplitude.

Digital electronics: elementary notions This chapter offers a fast outline of the basic elements that may be found in digital circuits: only a small fraction of the large number of IC devices commercially available will be analyzed. This brief digest should however be sufficient to give at least an idea of the working principles of most of IC digital devices and to provoke some curiosity into the reader who might deepen his knowledge elsewhere Logic circuits Digital logic circuits are those circuits where only two stable states are possible in any point of the network: e.

This means that the minimum output voltage in the H state of any device must always be higher that the high threshold input value for any device; and the maximum output voltage in the L state of any device must always be lower than the low threshold input value for any device. Millman and A.

Lancaster, or in Digital Electronics by W. Any complex digital circuit may be split into basic blocks named logic gates. In the graphic symbols the negation is marked by a small circle at the gate output, which indicates an added NOT gate. These equivalences, shown in Figure Table The first configuration does not allow connecting more gate-outputs together, while the second one allows to use many inverters with common output which makes a NOR with many inputs.

The drawback is that the pull-up resistor reduces the device speed. The power available at one TTL output can drive up to 10 gates we say it has a fan-out of 10 , with a maximum current to ground of about 0. The main families51 of TTL gates are 74xx and 54xx where xx stays for the number that specify the device. High-speed H , with faster switching than standard TTL 6ns but significantly higher power dissipation 22 mW.

Schottky S , operated more quickly 3ns but had higher power dissipation 19 mW Low-power Schottky LS good combination of speed 9. Bistable circuits: the flip-flop A flip-flop or latch is a circuit that has two stable states and can be used to store state information Two inverters in a closed loop as in Figure This circuit has memory, i.

The resistors in Figure Another RS flip-flop circuit is shown in Figure When the pulse is applied through a coupling capacitor as in figure With edge triggering the pulse duration has no effect e. In fact from Figure The symbol Q in the third column in truth table defines a stable state either 0 or 1.

Synchronous flip-flop The basic synchronous flip-flop is drawn in Figure A modification of this circuit, shown in Figure The synchronous latch of Figure A configuration that avoids multiple toggling is the master-slave flip-flop shown in Figure Here two identical synchronous latches in series are triggered by the CLOCK pulse: an inverter provides the needed counter phase trigger for the two latches.

If R and S ports are connected by an inverter, as in Figure The type-D flip-flop transfers the logic value of the input D to the output Q when the clock goes low; it is therefore a negative-edge triggered device. If the output Q is shorted to the input D, as in Figure Note that the output is always a square wave.

Adding two AND gates to a synchronous latch, as in Figure Monostables A monostable is a device that gives an output pulse with preset width one-shot pulse when a suitable signal trigger is fed to the input. An example made of two NOR gates is shown in Figure The trigger is applied to the first gate whose output is fed, through an high-pass filter, to the second gate input. The trigger pulse is any signal with a fast rising edge with amplitude lager that 3V.

The working principle is the following. The output of gate 2 is "0" because its input B2 is "1" due to the bias resistor R. The output of gate 1 is "1" because its input B1 is "0" due to Figure The diodes protect the gates inputs from over voltages due to the high-pass filters.

If A2 is kept "high" one-shot enabled the output toggles at the B2 spike trigger, if A2 is kept "low" one-shot disabled no toggling occurs. An equivalent Figure Here the trigger must be a "high" pulse that lasts longer than the output "low" pulse. The stable state is "0" at input and "1" at output. The rising edge of the trigger pulse toggles the first NAND inverter , as well as the second Figure The examples of monostable circuit above described give an idea of the working principle of one- shot devices; however there are commercially available IC that implement monostable e.

These devices requires only external RC for setting the output pulse width. Astables Chapter 9 described several examples of astable multivibrators made by comparators plus RC negative feedback. Much more compact astable multivibrators can be made using logic ports, as shown in Figure The Schmitt trigger is simply a comparator with hysteresis This circuit offers two output in phase opposition, but the signals are square wave only when the threshold voltages are symmetric with respect to the bias voltages e.

A trick for Q adjusting separately the two time constants we may R1 R2 use the circuit shown in Figure The square wave frequency in this circuit is not exactly predictable: it does depend on temperature and on bias voltage. Monostable with delay The delay generated by an odd chain of inverters may be used to build a monostable one-shot circuit as in the two examples shown in Figure Only after the delay T also the input B changes state, thus toggling the output.

Delay generator A simple delay generator may be obtained with the circuits shown in Figure By connecting these two circuits in series with identical RC the input pulse will be reproduced at the output with the delay T. Some special IC In this chapter we describe some popular IC that do not belong to the categories illustrated in the previous chapters: timers, IC voltage sources, analog switches. The timer: a simplified description The IC timer is made essentially by two comparators, one RS flip-flop, two transistors one switch and one inverter.

An essential drawing is shown in Figure The shown circuit behaves as monostable pulser Figure The output may be forced "low" anytime by setting "low" the reset port that switches ON the transistor T2, which in turn switches ON transistor T1. The timer The most commonly used IC timer is Its connection diagram is the one shown in Figure A monostable pulser made with timer We add to the circuit of Figure The dual-type two timers inside the same chip is named An astable pulser made with timer If we short the trigger pin to the threshold pin and we connect the discharge pin to the voltage divider R1,R2 that charges the capacitor C, as in Figure At this time the ———— 58 Alternatively the input pulse must be shorter that the output pulse.

At this time the comparator C1 toggles switching-on T1, and the system reverts to the initial state. Another way to obtain a better Symmetry is by adding a diode in parallel to R2, as shown in Figure A square wave generator A pure square wave generator may be obtained from a timer as shown in Figure An auxiliary output signal load RL is available at the discharge pin.

A linear voltage-to-frequency converter In chapter 10 , figure IC voltage reference Chapter 6 describes some voltage reference sources made with zener and OA with negative feedback. These circuits, however, are also commercially available as compact IC that may be classified in 5 classes: two-terminal devices band gap voltage reference , programmable zener, three-terminal fixed-voltage sources, three-terminal adjustable regulators, and four-terminal adjustable regulators.

Many values are available for VZ, e. Without voltage divider R1 , R2 the devices behaves as a normal zener. The three-terminal fixed-voltage sources Figure With a minimum bias voltage of a few mA they may Figure The 3-terminal adjustable regulator typical wiring is shown in Figure The output voltage Vo ranges from 1.

The value of resistor R2 may go down to zero for minimum Vo. The wiring in the 4-terminal adjustable regulator is similar, but here the role of the two resistors in the voltage divider is exchanged see Figure Analog switches The ideal switch may be defined as a bi-stable two-terminal device that an external action may toggle between zero resistance Ron and infinite resistance Roff.

The external command may be mechanic e. The real switch differs from the ideal one because the resistance Ron in the "closed" state is not zero and the resistance Roff in the "open" state is not infinite. The advantages of analog switches are mainly their speed, and the possibility of use low-power command signals. In the first case the current must flow through the two terminals of the switch in a given direction unipolar switch , in the second case in both directions bipolar switch, i.

There are many commercially available IC analog switches, with various configurations: double, quad or even more switches integrated inside a single chip. It must be biased by a maximum Figura The maximum current is 10 mA. More sophisticated CMOS quad bilateral switches are the models and The block diagram is shown in figures The first type has the 4 switches normally closed with command voltage is "low" , while the second type has the 4 switches normally open..

The command threshold voltage ranges Figure The threshold voltage may be adjusted through the VR pin. Transducers, sensors and interfacing techniques The name transducer defines a device that transforms a signal expressed in a physical quantity temperature, velocity, magnetic field Transducers are usually divided into two classes: sensors and actuators: The name sensor defines a device that converts the value of a physical quantity, or its changes into an electrical signal.

The name actuator defines a device that converts electrical signals into changes of some physical quantity. Some transducers are reversible: they may be used either as sensors or as actuators. We well consider, as examples, transducers for four physical quantities: temperature, force , light, and position. The temperature transducers may be used as thermometers, but also as level sensors, flux sensors, thermal conductivity sensors, Temperature sensors Temperature sensors may be divided in three broad classes: resistive sensors, diodes, and thermocouples.

Resistance thermometers The resistive temperature detectors RTD may be metals, semiconductors or carbon-resistors. The metallic RTD are usually made of copper, nickel or platinum. The platinum RDT are the most reliable because a Pt wire may be produced with very small impurity content, which makes the temperature coefficient of the sample highly reproducible but they are very expensive. They must be biased by a constant d.

Their sensitivity is limited by the Joule self-heating, which requires reducing the bias current and therefore the signal amplitude. The simplest method to measure a resistance Rx is the voltamperometric method: we measure the voltage drop Vx across Rx due to the known current Ip flowing through it. By keeping constant Ip the Rx measurement reduces to Vx measurement. This circuit allows reading the temperature of the body thermally anchored to Rx in kelvin, Celsius, Fahrenheit, or its temperature changes with respect to a reference temperature.

This problem may be avoided replacing the d. An alternative method, that does not require a stabilized a. The value of the current Ip does not enter the balance equation, therefore we do not need a stable a. The advantage of these sensors is the small size and the wide range of resistance value.

Note that this technique gives an V2 VTm R output voltage increasing with temperature. A circuit suitable for diode thermometry is that shown in Figure A simpler circuit is shown in Figure The potentiometer P2 provides the zero-scale Figure The thermocouple The thermocouple is a temperature sensor that exploits the temperature dependence of the electromotive force emf in a junction of two different metals Seebeck effect This emf VTC is an increasing function of T, almost linear near room temperature with a temperature coefficient!

The main advantages of these sensors are: 1 speed, due to small mass; 2 easy thermal coupling; 3 extended working range, from 10 K to K; 4 low cost; 5 no bias needed To avoid the measurement of the room temperature, we may add a reference junction kept at a fixed known temperature To , e. In place of the usual ice-bath for the reference junction, the room temperature changes may be accounted for by an electronic automatic correction provided by a diode thermometer.

An example of this approach is shown in Figure The differential amplifier A1 must have high input impedance in order to make negligible the thermocouple wires resistance changes, and a high gain G because the source signal is of the order of few mV: with type J changes of 0. Pin 4 and pin 7 are the negative and positive voltage power supply terminals. The power which is required for the IC to function is received from both these pins. The voltage level between these pins can be in the range of 5 — 18V.

The output which is delivered from the IC op amp is received from this pin. The output voltage that is received at this pin is based on the feedback approach that is used and the voltage level at the input pins. In the same way, when the voltage value at pin 6 is low, this corresponds that output voltage is similar to the -ve supply voltage. These are the input pins for the operational amplifier.

Pin 3 is considered as the inverting input while pin 3 is considered as the non-inverting input pin. As before discussed, this operational amplifier has an increased level of voltage gain. In order to overcome this, an offset value of the voltage to be applied at pin 1 and pin 5, and this generally accomplished by a potentiometer. It is just a pin that is used to fill up the empty pin in the IC Op Amp.

It has no connection with any of the internal or external circuits. This section clearly explains the concept of the internal schematic and working of IC A typical IC is constructed with a circuit that is included with 11 resistors and 20 transistors. All these transistors and resistors are assimilated and connected as a single monolithic chip. Here, for the transistors, Q1 and Q2, the inverting and non-inverting inputs are connected correspondingly.

These Q3 and Q4 operate as common-base amplifiers. This type of configuration isolates the inputs that have a connection with Q3 and Q4 and so eliminates likely signal feedback which might take place. The voltage fluctuations that take place at the operational amplifier inputs might show an impact on the internal circuit current flow and also impacts the effective functional range of any transistor that is in the circuit. So, to eliminate this from taking place, there has been the implementation of two current mirrors.

The transistor pairs Q8, Q9 and Q12, Q13 are connected in a way to form mirror circuits. As Q8 and Q12 transistors are the regulating transistors, they set the voltage level at the EB junction for their corresponding pair of the transistor. This voltage level can be accurately regulated to some decimals of millivolts and this accuracy permits only necessary current flow to the circuit. One mirror circuit which is developed by Q8 and Q9 is fed to the input circuit whereas the other mirror circuit developed by Q12 and Q13 is fed to the output circuit.

Also, the other mirror circuit which is the third one formed by Q10 and Q11 functions as an increased impedance connection between the -ve supply and input. This connection offers a reference level of voltage showing no loading effect on the input circuit. The transistor Q6 together with 4. This is achieved to eliminate any kind of signal variations at the output amplifier section. The below sections explains the experimental procedure of integrator and differentiator using IC op amp theory.

The integrator circuit using op amp is shown below. To form an integrator circuit and to know the output, the circuit connection to be done as explained in the below steps:. The differentiator circuit using op amp is shown below. To form a differentiator circuit and to know the output, the circuit connection to be done as explained in the below steps:.

The easiest approach to implement IC Op Amp is to function it in the open-loop configuration. The open loop configuration of IC is in inverting and non-inverting modes. In an IC op amp, pin2 and pin6 are the input and output pins. When the voltage is given to the pin-2 then we can get the output from the pin In an IC operational amplifier pin3 and pin6 are input and output pins.

When the voltage is given to the pin3 then we can get the output from the pin The applications mainly include an adder, comparator, subtractor, voltage follower, Integrator, and differentiator.

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