Rc coupled amplifier pdf

Moreover, Ce cannot shunt the emitter resistance Re effectively because of its large reactance at low frequencies. These two factors cause a falling of voltage gain at low.

This increases the loading effect on next stage and serves to reduce the voltage gain. Moreover, at high frequency, capacitive reactance of base-emitter junction is low which increases base current.

This reduces current amplification factor. Due to these reasons the voltage gain drops at high frequencies. The effect of coupling capacitors in this frequency range is such so as to maintain a uniform voltage gain. Thus, as the frequency increases in this range , reactance Cc decreases which tends to increase the gain.

However , at the same time, lower reactance means higher loading of first stage and hence lower gain. These two factors cancel each other , resulting in. This presentation explains the working of different diode clipper circuits like Positive and Negative Diode Clippers, Biased Clipper circuit, and Combinational Clipper Circuit with the help of circuit diagrams and waveforms.

In order to fix the clipping level to the desired amount, a dc battery must also be included. When the diode is forward biased, it acts as a closed switch, and when it is reverse biased, it acts as an open switch. Different levels of clipping can be obtained by varying the amount of voltage of the battery and also interchanging the positions of the diode and resistor.

There are two general categories of clippers: series and parallel or shunt. The series configuration is defined as one where diode is in series with the load, while the shunt clipper has the diode in a branch parallel to the load.

Depending on the features of the diode, the positive or negative region of the input signal is clipped off and accordingly the diode clippers may be. Positive Diode Clipper In a positive clipper, the positive half cycles of the input voltage will be removed. During the positive half cycle of the input waveform, the diode D is reverse biased, which maintains the output voltage at 0 Volts.

Thus causes the positive half cycle to be clipped off. During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. During the positive half cycle, the diode D is forward biased and the diode acts as a closed switch. This causes the diode to conduct heavily. This causes the voltage drop across the diode or across the load resistance RL to be zero.

Thus output voltage during the positive half cycles is zero, as shown in the output waveform. During the negative half cycles of the input signal voltage, the diode D is reverse biased and behaves as an open switch. Consequently the entire input voltage appears across the diode or across the load resistance RL if R is much smaller than RL. The negative clipping circuit is almost same as the positive clipping circuit, with only one difference.

If the diode is reconnected with reversed polarity, the circuits will become for a negative series clipper and negative shunt clipper respectively. The negative series and negative shunt clippers are shown:. In all the above discussions, the diode is considered to be ideal one.

In a practical diode, the breakdown voltage will exist 0. When this is taken into account, the output waveforms for positive and negative clippers will be of the shape shown in the figure below. A biased clipper comes in handy when a small portion of positive or negative half cycles of the signal voltage is to be removed. When a small portion of the negative half cycle is to be removed, it is called a biased negative clipper. In a biased clipper, when the input signal voltage is positive, the diode D is reverse-biased.

This causes it to act as an open-switch. Thus the entire positive half cycle appears across the load. When the input signal voltage is negative but does not exceed battery the voltage V, the diode D remains reverse-biased and most of the input voltage appears across the output.

When during the negative half cycle of input signal, the signal voltage becomes more than the battery voltage V, the diode D is forward biased and so conducts heavily.

Thus a biased negative clipper removes input voltage when the input signal voltage becomes greater than the battery voltage. When a portion of both positive and negative of each half cycle of the input voltage is to be clipped or removed , combination clipper is employed.

In series clippers, when the diode is in OFF position, there will be no transmission of input signal to output. But in case of high frequency signals transmission occurs through diode capacitance which is undesirable.

This is the drawback of using diode as a series element in such clippers. In shunt clippers, when diode is in the off condition, transmission of input signal should take place to output. But in case of high frequency input signals, diode capacitance affects the circuit operation adversely and the signal gets attenuated that is, it passes through diode capacitance to.

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Explore Audiobooks. Bestsellers Editors' Picks All audiobooks. Explore Magazines. Editors' Picks All magazines. Explore Podcasts All podcasts. Difficulty Beginner Intermediate Advanced. Explore Documents. Uploaded by Ayesha Gupta. Document Information click to expand document information Description: ppt. Did you find this document useful? Is this content inappropriate? Report this Document. Description: ppt. Flag for inappropriate content. Download now. When an AC input signal is applied to the base of first transistor, it gets amplified and appears at the collector load R L which is then passed through the coupling capacitor C C to the next stage.

This becomes the input of the next stage, whose amplified output again appears across its collector load. Thus the signal is amplified in stage by stage action. The important point that has to be noted here is that the total gain is less than the product of the gains of individual stages.

This is because when a second stage is made to follow the first stage, the effective load resistance of the first stage is reduced due to the shunting effect of the input resistance of the second stage. Hence, in a multistage amplifier, only the gain of the last stage remains unchanged. As we consider a two stage amplifier here, the output phase is same as input.

Because the phase reversal is done two times by the two stage CE configured amplifier circuit. Frequency response curve is a graph that indicates the relationship between voltage gain and function of frequency.

The frequency response of a RC coupled amplifier is as shown in the following graph. From the above graph, it is understood that the frequency rolls off or decreases for the frequencies below 50Hz and for the frequencies above 20 KHz. The capacitive reactance is inversely proportional to the frequency. At low frequencies, the reactance is quite high. The reactance of input capacitor C in and the coupling capacitor C C are so high that only small part of the input signal is allowed.

The reactance of the emitter by pass capacitor C E is also very high during low frequencies. Hence it cannot shunt the emitter resistance effectively. With all these factors, the voltage gain rolls off at low frequencies. Again considering the same point, we know that the capacitive reactance is low at high frequencies.

So, a capacitor behaves as a short circuit, at high frequencies. As a result of this, the loading effect of the next stage increases, which reduces the voltage gain.