# ELECTRONIC CIRCUIT ANALYSIS TEXTBOOK PDF

Electronic Circuit Design and Analysis aspects are dealt with in this book. Learning these topics is very essential for any electronics engineer. A student must. textbook. Many of the sections and figures need to be revised and/or are missing. Please check . signals greatly simplifies the analysis of electronic circuits. Theory And Design Of Electrical And Electronic Circuits - galileu This book is for people who want to learn basic electricity, electronics Teach Yourse.

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C, with design aspects are given. S and C. G configurations are also given. The modification in the characteristics of the input signal can be with respect to voltage, current, power or phase. Anyone or all these characteristics power, or phase may be changed by the amplifier circuit. RF Radio Freq. Direct coupled 2. RC coupled 3. Transformer coupled 4. LC Tuned Amplifiers 5. Series fed. Low power tens of mW or less.

Medium power hundreds of mW. High power Watts. Switching type. If the output resistances are equal decibel voltage gain is equal, to power gain. Overall db V of a multistage amplifier is equal to sum of db V of individual stages.

It is called as feedback capacitor. When the gain K is large, the feedback will change the input Z and output Z of the circuit. So according to the Miller's theorem, the feedback capacitor can be split into two values, one as connected in the input side and the other on the output side, as shown in Fig. The AC current passing through capacitor C in Fig. Vo is low since I is low. As f increases Xc decreases.

Hence I flows, and V0 increases. Gain increases. Hence the frequency response is as shown. Therefore it is also called as half power point. The coupling capacitor ml. This is known as Stiff Coupling. Multistage Amplifiers 2. Usually, it is rounded off to 3.

Bec,ause, for the circuit shown. A change of 20db per decade change in frequency. An Octave is a factor of 2 in frequency change Whenf changes from to Hzs, it has changed by one octave. Multistage Amplifiers 65 When,f changes from to Hzs, it is two octaves for lead network, Bode Plot is 0. Common Collector Amplifier circuit has high input impedance and low output impedance. But its Av r,..

The input resistance of the second transistor constitutes the emitter load of the first transistor. So, Darlington Circuit is nothing but two transistors in Common Collector Configuration connected in series. The same circuit can be redrawn as AC equivalent circuit.

So, DC is taken as ground shown in Fig. Hence, 'C' at ground potential. So, we can assume that infinite resistance is connected between emitter and collector. For the analysis of the circuit, consider the equivalent circuit shown in Fig. Therefore, Darlington Circuit has very high input impedance and very large current gain compared to Common Collector Configuration Circuit. Therefore, the characteristic of Darlington Circuit are 1. Very High Input Resistance of the order of M. Very Large Current Gain of the order of 10, Very Low Output Resistance of the order offew.

Voltage Gain, Av 2. The quiescent or operating conditions of both the transistors will be different. The second drawback is leakage current of the first transistor Q I which is amplified by the second transistor Q2 -: Leakage Current is the current that flows in the circuit with no external bias voltages applied a The h-parameters for both the transistors will not be the same. Darlington transistor pairs are in single package available with hje as high as 30, 2.

Higher input resistance cannot be achieved because of the biasing resistors RI , R2 etc. The input resistance can be increased greatly by boot strapping, the Darlington Circuit through the addition of Co between the first collector C I and emitter B 2. What is Boot Strapping? Therefore, the input resistance of the circuit as seen by the generator is R.

Now suppose, the bottom end of R is not at ground potential but at higher potential i. When V increases KV also increases. K is constant. Both the top and bottom of the resistor terminals are at the same potential. This is called as the Boots Strapping method which increases the input resistance of a circuit. If the potential at one end of the resistance changes, the other end of R also moves through the same potential difference. It is as if R is pulling itself up by its boot straps.

For Common Collector Amplifier, h. If the input signal changes by Vj' then E2 changes by Ay. V j assuming the resistance of Co is negligible. The value ofXco is chosen such that at the lower frequencies, under consideration XCo is a virtual short circuit. If the collector C 1 changes by certain potential, E2 also changes by the same amount. So C 1 and E2 are boot strapped. There is 1 h ob between BI and C 1. B configuration 73 Multistage Amplifiers The circuit is shown in Fig.

The collector current of transistor Q equals the emitter current of Q2. Let us consider the input impedance h etc. We can conclude that the collector of Q is effectively short circuited. Therefore C is virtually shorted to the ground. Ihi 2. Therefore, output conductance of the entire circuit is h22 2. Its output resistance is equal to that of a single Common Base Transistor hob ' The reverse voltage gain is very very small, i. Transistor Since hIe and h fe are same with negligible internal feedback:.

It is convenient if we start with the II stage. II Stage: The first stage in Common Emitter CE configuration provides voltage and current gains. The second stage in Common-Collector CC configuration provides impedance matching. This circuit is used in audio frequency amplifiers. The circuit is shown in Fig. II Stage in CC amplifier: RL hoc RLI.: It blocks the DC components present in the output orI Stage from reaching the input of the II stage which will alter the biasing already fixed for the active device.

Resistor Rg is connected between gate and ground resistor Ro is connected between drain and VDO supply. C S IS the bypass capacitor used to prevent loss of gain due to negative feedback. The active device is assumed to operate in the linear region. So the small signal model of the device is valid. Frequency Roll-off is the term used for the decrease in gain with frequency in the upper cut-off region. In the logarithmic scale of frequency, octave.

If JFETs are employed, common source configuration is used. The function of this is to amplify the difference between the signals. The advantage with this amplifier is, we can eliminate the noise in the input signals which is common to both the inputs.

Thus SIN ratio can be improved. But the above equation will not correctly describe the characteristic of a differential amplifier. Vo should be Ad IlV. So in both cases. VI should be the same. Al and A2 are the voltage gains of the two amplifier circuits separately. We want Ad to be large and Ac to be very small because only the difference of the two signals should be amplified and the average of the signals Ad should not be amplified. This should be large for a good difference amplifier. C amplifier viz.

C and C. E, the output is measured with respect to ground. But in difference amplifier, the output is a. So Vo is not measured w. The advantage with this type of amplifiers is the drift problem is eliminated.

Drift is reduced in this type of circuit, because, the two points should be exactly identical. The input to a differential amplifer are of two types. Differential mode 2. Common mode.

IA is an I. C ditferential amplifier. Input is given to pins 2 and 3. Output is taken at pin no 6.

## ELECTRONIC CIRCUIT ANALYSIS - ECA Study Materials

In the difference amplifier, the difference of the input voltages V j and V2 is amplified. They are not at ground potential. So the output voltage is not at ground potential. Hence the output voltage is the difference of the collector voltages a. So difference amplifiers are used to measure very small increased voltages.

Because there should be no common mode signal, while computing A" AI is the actual gain. Not differential gain. So this is known as the swimming junction. Electronic Circuit Analysis 84 1.

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Expression for Ay H. F is, Ay H. Phase shift 8. Expression for Ay L. Figure of Merit of an amplifier circuit is Expression for Vo interms of Ad' Vd, Vc and pis, Expression for Ad and Ac interms of At and A2 are Stiff coupling is When frequency change is octave Phase response is a plot between What is distortion?

What are the types of distortion? Define them. How does the amplifier behave for low frequencies and high frequencies? Which configuration is the best in cascade for an output stage and for an intermediate stage?

What is the darlington pair? What is its significance? How is the bandwidth of a cascade affected compared to the bandwidth of a single stage? Why is the emitter bypass capacitor used in an RC coupled amplifier?

What is the affect of emitter bypass capacitor on low frequency response? What are types of cascade? How would you differentiate an interacting stage from a non-interacting stage?

What is the expression for the upper 3dB frequency for a n-stage non interacting cascade? What is the expression for lower 3dB cutoff frequency in n-stage interacting cascade?

What is the expression for upper 3dB cutoff frequency in a n-stage interacting cascade? What is the slope of the amplitude response for an n-stage amplifier?

Why do we go for multistage amplifier? Electronic Circuit Analysis 86 1. Explain about the classification of Amplifiers based on type of coupling and bandwidth. What are the different types of distortions possible in amplifiers outputs?

Obtain the expression for the voltage gain Av in the L. F and H. F ranges, in the case of single stage BJT amplifier. With the help of necessary waveforms, explain about the step response of amplifiers. What is the significance of square wave testing in amplifiers? Draw the circuit for differential amplifier and derive the expression for CMRR.

Explain about the characteristics of operational amplifiers. Explain its working, obtaining overall values of the circuit for h" hI' ho and h, Multistage Amplifiers 87 1.

VC] P Vd Phase angle and frequency Leakage current is more Very high CE-CB Large voltage and current gains If the 04tput waveform is not the replica of the input waveform, it is called distortion. If different frequency components are amplified differently, it is called frequency distortion.

If the output is shifted by different phased each time, it is called phase distortion. Low frequencies - high pass filter. High frequencies - low pass filter. CC-CC cascade is called Darlington pair. It decreases. To decrease the loss in gain due to negative feedback The tilt is more Interacting and non interacting.

If the input impedance of next stage loads the previous stage, it is calleajnteracting stages. If the input impedance of next stage does not load the previous stage, it is called non interacting stage. For high gain. If '1' of the input is high MHz and the amplitude of the input signal is changing the Transistor amplifier will not be able to respond. What is the reason for this? It is because, the carriers from the emitter side will have to be injected into the collector side.

These take definite amount of time to travel from Emitter to Base, however smalt-i'rmay be. But if the input signal is varying at a much higher speed than the actual time taken for the carries to respond, then the Transistor amplifier will not respond instantaneously. Thus, the junction capacitances of the transistor, puts a limit to the highest frequency signal which the transistor can handle. Thus depending upon doping area of the junction etc, we have transistors which can respond in AF range and also RF range.

To study and analyze the behavior of the transistor to high frequency signals an equivalent model based upon transmission line equations will be accurate. But this model will be very complicated to analyze. So some approximations are made and the equivalent circuit is simplified. If the circuit is simplified to a great extent, it will be easy to analyze, but the results will not be accurate.

If no approximations are made, the results will be accurate, but it will be difficult to analyze. The desirable features of an equivalent circuit for analysis are simplicity and accuracy. Such a circuit which is fairly simple and reasonably accurate is the Hybrid-pi or Hybrid-;rmodel, so called because the circuit is in the form of 7r. The parameter have units of fl, U etc. So it is a hybrid circuit. Hence it is called as hybrid-;r model. Using this model a detailed analysis of single stage Common Emitter Transconductance amplifier is made.

E BJT Model High Frequency Transistor Circuits 91 Analysis ofthis circuit gives satisfactory results at all frequencies not only at high frequencies but also at low frequencies. All the parameters are assumed to be independent of frequency. It is not physically accessible. The base spreading resistance rb'b is represented as a lumped parameter between base B and internal node B'.

Vb'e is the input voltage across the emitter junction. If Vb'e increases, more carriers are injected into the base of the transistor. So the increase in the number of carriers is l Vb'e.

This results in small signal current since we are taking into account changes in Vb'e. This represents the current that results because of changes in Vb'e' when C is shorted to E.

When the number of carriers injected into the base increase, base recombination also increases.

So this effect is taken care of by gb'e. As recombination increases, base current increases. Minority carrier storage in the base is represented by Ce' the diffusion capacitance. According to Early Effect, the change in voltage between Collector and Em! So base width will be modulated according to the voltage between Collector and Emitter. When base width changes, the minority carrier concentration in base changes.

Hence the current which is proportional to carrier concentration also changes. So IE changes and hence Ie changes. This feedback effect [IE on input side, Ie on output side] is taken into account by connecting gb'e between B', and C. The conductance between Collector and Base is gee. Ce represents the collector junction barrier capacitance. Temperature 2. Value of Ie 92 Electronic Circuit Analysis 3.

So negative voltage is given. Since Ic is negative. So in the hybrid-1t equivalent circuit which is valid at low frequencies, all the capacitances can be neglected. The equivalent circuit is as shown in Fig. If output is shorted, i. In h-parameters it is represented as hoe. Collector junction is reverse biased.

## Electronic Circuit Analysis Pdf Notes – ECA Pdf Notes

High Frequency Transistor: IE and is independent of Temperature T. So ifE-B junction is forward biased, holes are injected into the base. The distribution of these injected holes between E and C is as shown. The collector is reverse biased.

So the injected charge concentration p' at the collector junction is zero since they are attracted because of the negative potential at the collector. The base width W is assumed to be small compared to the diffusion length Ls of the minority carriers. Average concentratIOn. Hence, the hybrid-n model is valid only when change in VBE is very small and so change in IE is equal to change in Ic' i.

So change in IE is equal to change in Ic' Giacoletto who proposed the hybrid - n model, has shown that the hybrid parameters are independent of frequency when W2 2nf. Hybrid "model is valid for frequencies upto Vr e Emitter Capacitance C.

So rbb' decreases, because of conductivity modulation. But rbb' increases with increase in Temperature. Because as T increases, mobility of the carriers decreases. So conductivity decreases. So rbb, increases. Transistor amplifier circuit. The hybrid-1t equivalent circuit is as shown: Therefore gee disappears. The current is delivered to the output directly through Ce and gb'c is also neglected since this will be very small.

Common Emitter short circuit current gain was skipped out. This indicates the high frequency performance of the transistor. Jp hfe is the short circuit current gain. ThereforefT is the short circuit current gain Bandwidth product. So if we have two transistors with same fT' the transistor with low hfe will have larger Bandwidth and vice versa.

To determine the fr of a given transistor, we need eRO whose frequency range is of that order. Such a eRO is not common. Because, there are two time constants associated with the input and the other associated with the output. The output time constant will be much smaller than the input time constant. So it can be neglected. So this can be neglected compared to gb'e On the output side between collector and emitter as K -1 Cc-K rb'c.

So it is open circuit.

IL is contributed by the current soutce only. Is the frequency at which the short circuit gain in common emitter configuration falls by 3 db. This is defined as the frequency at which the common emitter shunt circuit current gain becomes 1. But as frequency increases Ai falls. Why should Ai decrease?

Ai I As frequency increases, Xe increases. So, Xe increases. Due to this, less number of carriers will reach collector.

Storage of carriers at the base and emitter increases.

So Ie decreases. Therefore IL decreases i. Hence Ai decreases. IT depends on the operating point of the transistor. CDe W2 But Find the value of the source resistance that will give the required bandwidth.

The h-parameters equivalent circuit in Common Emitter configuration is as shown in Fig. We have to show that the hybrid 1t equivalent circuit will also be the same with the approximation given in the problem. Electronic Circuit Analysis Solution: So draw a line between base B and B'. We have rbb" So draw another line to indicate B'. Between B' and E, we have Cb'e parallel with rb'e' So draw these two in parallel and indicate point E. E and B are input points. C and B are output points.

Between r ce E c Base and Collector are to be shorted. So short Collector and Base terminals. Hence replacing L by equivalent R can be done only when the output current is small. But the resulting circuit becomes very complicated. By making approximations, it becomes simple, but the analysis may not be accurate.

So hybrid-x model is a compromise between the two. Model Common Emitter model which is valid at high frequencies is called hybrid-x or Giacoletto model.

It is as shown in Fig. By analyzing the circuit we get results which will agree with practical results at all frequencies. All the hybrid - 7r parameters are assumed to be independent offrequency. High Frequency Transistor Circuits 3. This is taken into account by the conductance gb'e between B' and E.

The excess minority carriers stored in the base is accounted for by the diffusion capacitance Ce' The feedback effect between input and output is taken into account by conductance gb'e' Ce is collector junction barrier capacitance.

Neglecting all the capacitances, Fig. From Fig. Transistor when held with leads upwards E is on left half side. The upper half semicircle is emitter. It is usually specified as Cob by the manufacturers. In the active region, collector junction is reverse biased, C c is the transition 1t capacitance and varies as VcEtn where TI is C e: It represents the sum of emitter diffusion capacitance C De and emitter junction capacitance C Te.

Therefore Diffusion capacitance is proportional to emitter bias current IE' Hybrid - 1t models are valid for frequencies upto l'l: It is defined as the frequency at which the common emitter short circuit current gain becomes 1. It is independent of VCE' It varies inversely with temperature, Incremental transconductance of a transistor.

Electronic Circuit Analysis 2. Make reasonable assumptions. Table 3. Symbol Parameter Min. High Frequency Transistor Circuits To find C e ' C 1t , incremantal capacitance in hybrid - 7t model. Use typical values. Make reasonable approximations. Incremantal resistance in hybrid - 1t model. V CE' Parameters 1. If number of amplifier stages are cascaded, the output current is made up from several transistors and the individual device operating point canbe made to correspond to the optimem Gain - B.

A single section of a multi stage amplifier is shown in Fig. The input impedance of the amplifier circuit is low compared to the impedance of the parallel R-C network. Electronic Circuit Analysis Now consider 3 such stages cascaded as shown in Fig.

R is the series resistor and hie is the transistor low frequency input impedance. U2 U2 L U2 Fig. RL is a 50 n load for the circuit. The voltage gain gets multiplied for each stage. The Voltage Gain for 'm' cascaded stages is, y'G m V. The approximate high frequency equivalent circuit for a BJT operating in C.

The equivalent input impedance of the R-C combination on the input side along with transistor capacitances is shown in Fig. The Bandwidth B. Design a single stage I. The small signal hybrid 1t parameters are: The circuit diagram is shown below To next stage Fig. C;y is calculated as 9 pF. Ro must be matched with the load R, of the next stage. I The feedback components, resistor Rn and capacitor Cn can be determined as, Qc Expression for gb'.

Expression for h,. Relation betweenfr, hr. Expression for C. If hr. Classify amplifiers depending on the position of the quiescent point of each amplifier. Draw the hybrid -1t model for a transistor in CE configuration. What isfr? What is the significance of the gain bandwidth product?

What would you neglect while drawing a low frequency model? How does the trans conductance gm depend on temperature? Write the expression for rbe in terms of gm and h,.

Ie How does the diffusion capacitance depend on current and temp? Write the expression for CD. When is the hybrid - 1t model valid? What is an emitter follower? Which time constant is considered for the bandwidth? What is the expression for Electronic Circuit Analysis 1. Draw the high frequency equivalent circuit of a BJT and explain the same. Derive the expressions for Hybrid -1t parameters. Derive the expression for the Hybrid - 1t parameters gm' ree, Ce and rb'e, gee.

Explain about Hybrid -1t capacitances. How do Hybrid -1t parameters vary with temperature? Obtain the expressions for lfi andlT of a transistor. Obtain the expression for the Gain Bandwidth product of a transistor.

High Frequency Transistor Circuits 1. Giacoletto model 2. The parameters are of different units Hybrid in 1t - shape. Fictitious terminal 4. The shape of the circuit is K. Incremental resistance. Picofarads Frequency at which short circuit current gain is unity.

Electronic Circuit Analysis Cde a. T" W2 CC Such electronic amplifier circuits, delivering significant output power to the load in watts range are termed as Power Amplifiers. Since the input to this type of amplifier circuits is also large, they are termed as Large Signal Amplifiers. In order to improve the circuit efficiency, which is the ratio of output power delivered to the load Po to input power, the device is operated in varying conduction angles of 0 0 0 , less than etc.

But if the input signal is large in magnitude, the operating point is driven over a considerable portion of the output characteristic of the triinsistor BJT. The transfer characteristic indicates the change in ic when Vb or IB is changed. For equal increments of VBE, increase in Ie will not be uniform since output characteristics are not linear for equal increments ofVBE , Ie will not increase by the same current.

So the transfer characteristic is not linear. Hence because ofthis, when the magnitude of the input signal is very large, distortion is introduced in the output in large signal power amplifiers.

To eliminate distortion in the output, pushpull connection and negative feedback are employed. Ie r Q operating point , I Fig. Power Amplifiers 4. So output power will be more and conversion efficiency ll is more. Since the transistor Q point is beyond cutoff, the output is zero or the transistor will not conduct. Output power is more because the complete linear region is available for an operating signal excursion, resulting from one half of the input wave.

The other half of input wave gives no output, because it drives the transistor below cutoff. Distortion is very high. These are used in radio frequency circuits where resonant circuit may be used to filter the output waveform. Class A and class B amplifiers are used in the audio frequency range. Class B and class C are used in Radio Frequency range where conversion efficiency is important. Amplifiers Here the magnitude of the input signal is very small, slightly deviating from the operating point.

But always the operation is in the active region only. The characteristics of the device can be assumed to be linear. The magnitude of the signal m: The operating point or Quiescent point Q swings with the input signal. Because the input signal magnitude is small, the operating point is in the active region only.

Because of the large swing Of the input signal, the non linear portion of the transistor characteristics are also to be considered. Hence the linear equivalent circuit analysis is not valid. So for large signal amplifiers only graphical analysis is employed.

Power amplifiers, class A, class B, class C amplifiers, push-pull amplifier are of this type. Large signal amplifiers are used where the output power requirement is large. Ifwe use small signal amplifiers, the number of stages to be cascaded will be large, complicating the circuit. Factors to be considered in large signal amplifiers: Output power 2. Distortion 3. Operating region 4.

Thermal considerations 5. Efficiency 11 Amplifier circuits may be classified in terms of the portion of the cycle for which the active device conducts. The device is Class A biased in that way. Series fed 2. RL is in series with Vcc. There is DC power drop across RL. I Power Amplifiers 4. DC drop across the primary of the transformer is negligible. There is no DC drop across RL.

Vyand Iy are the root mean square rms values of voltage and current. Therefore the operating point lies in the active region only. Let us assume that the static output characteristic of the transistor are ideal and linear. So if the input is a sinusoidal signal, then the output will also be sinusoidal. Let us use the subscripts y for output and x for input. Therefore ic So subscript y is used. Input is on x-axis.

So subscript 'x' is used. The output power Py can be found graphically. Output is on y-axis. Therefore the DC power input to the circuit is Vyy. Let RL be the load resistance. In addition to the DC drop across the load and AC drop across the load there is thermal power dissipation Po across the device, since it gets heated.

Now if there is no AC output power i. Therefore if AC power output is zero, ie. Therefore the device is cooler when delivering power to a load than when there is no such AC power transfer. When there is power drop across the device itself, it gets heated. Amplifier Certain assumptions are made in the derivation, which will simplify the estimation of the efficiency YJ.

Because of this some errors will be there and the expression is approximate. Power AmpUfiers The assumption is that the static output characteristic of the transistors are equally spaced, in the region of the load line for equal increments in the base current. If ib is increased by 1! Thus for the load line shown in the Fig. Vm is the voltage corresponding to the operating point.

Power Amplifiers VCC Since there is no DC voltage drop across the transformer. The coupling device should be such that, it allows only the AC signal to the amplifier circuits and blocks the DC components present in the signal generator, because we are interested in amplifying only AC signals.

For this purpose a capacitor can be used for coupling. Capacitor coupled amplifier 4. Direct coupled amplifier 2. Transformer coupled amplifier 3. RC coupled amplifier 5. C I and C2 are the coupling capacitors. They are chosen such that, for the lowest frequency signal to be amplified, Xc and Xc are I 2 Electronic Circuit Analysis short circuits. But because of these reactive coupling elements, as signal frequency decreases Xc increases.

Hence there will be large voltage drop across the capacitor and so the actual input to the amplifier reduces and hence gain decreases. Similarly at high frequencies because of the shunting capacitance C s' gain falls.

Therefore there is a particular frequency range in which gain is of desirable value only. Instead of capacitors, transformer can also be used for coupling. But what is the advaptage of the transformer coupling? Suppose, the load resistance RL is very small: Therefore impedance matching will not be there and so maximum power will not be transferred. Even if capacitive coupling is used, impedance matching cannot be achieved.

But this can be done using a transformer. Therefore the output voltage at the secondary of the transformer will be much smaller compared to the input voltage since stepping down action is taking place. But the current amplification will be there and because of Z matching, maximum power will be transferred to the load. Similar to resistive capacitor coupled amplifier, we have the frequency response which depends upon the inductance of the primary and secondary.

The transformer on the primary side is chosen such that the sotirce resistance of the generator matches with the input Z of the amplifier circuit. Transformer coupled amplifiers are used in low audio frequency range only because at higher frequencies the XL of the transformer will be large and so the gain falls. Another advantage with the transformer coupled amplifiers is the AC current passing through the load resistance RL results in only wastage of power, since we are interested in only AC output Power Amplifiers power.

Moreover passing DC current through the loudspeaker coil is not desirable since it produces hum or noise. Therefore if transformer coupling is done, DC component of current passing through the transformer can be avoided.

II Es Fig. CE is emitter bypass resistor. For AC it is short circuit. The equivalent circuit, in terms of h-parameters neglecting the biasing resistors and capacitors, also neglecting the input transformer and considering base and emitter as the input ports. Since it is a stepdown transformer, n n 1 is the inductance of the primary winding Since we are considering load referred to primary. In the mid frequency range, the inductive reactance X LP is high. Therefore it will not affect the response.

## Electronic circuit analysis and design

When impedance matching is done, the output Z of the circuit and the load resistance RL will be equal. Therefore the current will get divided between RL and the circuit equally.

The total current is hfe lb. Therefore the current through the primary of the transformer or in other words the current through the collector circuit is Thfi. Current gain 4. Instead of having coupling capacitors C I and C 2, we have transformer, coupling. The primary of transformer T2 acts as R. C2 across R2 helps in making Emitter of transistor at the ground point for AC. Because of CE, emitter is at ground potential for AC. Therefore secondary voltage of transformer is applied between base and emitter of transistor.

The input and intermediate stages operate in a small signal c1ass-A mode. Their function is to amplify the small excitation to a large value to drive the final device. So the output stage must be capable of delivering a large voltage or current or large power. Bias stabilization techniques and thermal runaways are very important with power amplifiers.

If the load resistance is connected directly in the output circuit as shown in FigA. In the case of loud speakers it is not desirable to pass DC current through the voice coil. So an arrangement is to be made using an output transformer. The impedance matching properties of an ideal transformer are: From the input characteristic IBmax to IBmin can be noted. If Po is average power dissipated by the active device.

A measure of the ability of an active device to convert DC power of the supply into AC power delivered to the load is called conversion l] or theoretical efficiency l].

It is also called collector circuit l] for transistor amplifier. Expression for instantaneous total current. Collector is reverse biased. Because ofRI and R2 the B-E junctions of the two transistors are forward biased so that cut in voltage Vr will not come into the picture.

For a given transistor, the dynamic characteristics are not exactly linear, that is, for some changes in the values of ib, ic will not change by the same amount that is. So the graph of Fig. Therefore for uniform changes in the input, the output will not change uniformly.

Hence,distortion will be introduced in the output waveform.II Stage: Untuned amplifiers: The magnitude of the input signal is very large. Because ofRI and R2 the B-E junctions of the two transistors are forward biased so that cut in voltage Vr will not come into the picture. Edition no. We have rbb" So draw another line to indicate B'. High power Watts. VI should be the same. Discuss about the effect of cascading on bandwidth of multistage amplifiers.

This produces a sinusoidal drain current.