Working of transformer coupled transistor amplifier tutorial
In this section of Electronic Devices and Circuits. This Section covers below lists of topics :. Transformer coupled amplifier 2. Atypical RC coupling Capacitor for a transistor amplifier is 0.
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Transformer Coupled Audio Power Amplifier
To get familiarity of fundamental concepts, design aspects and applications of. In Radio communications Fig. Tuned Amplifiers have several functions to perform in a Radio Transistor Receiver:.
Frequency response curve and Bandwidth of Tuned Amplifier Fig. Amplifier response voltage gain A V is large, at resonant frequency f 0 and is sharply lower before and after. Reduction in gain depends upon quality factor Q of the circuit. Frequency response of Tuned Amplifier is similar to that of a band pass filter. Let A m be the maximum value of Amplifier gain at f r.
On the frequency response characteristic of the Amplifier, two frequencies , f 1 as lower cut-off and f 2 as upper cut-off, are identified where the voltage gains are 0. In many applications, Amplifier response improves depending on how narrow the Amplifier bandwidth is.
Quality Factor Performance of a Tuned Amplifier depends upon the quality factor Q of the tuned circuit. Resonance curve of a parallel tuned circuit should be as sharp as possible in order to provide good selectivity. Sharp resonance curve means that impedance falls rapidly on either sides of the resonant frequency, as the frequency is varied from the resonant frequency f r.
Smaller the resistance of the coil, sharper is the resonance curve. Relation between quality factor Q and Bandwidth B. Quality of performance of Tuned Amplifier is known as figure of merit. Quality factor Q of the Tuned Amplifier is the ratio of centre frequency resonant frequency f r of the tuned circuit to the bandwidth B of the Amplifier:.
Q of the tuned circuit and the amplifier are same. Typical values of Q range from 50— General expression for bandwidth B of a tuned circuit. Bandwidth determines the selectivity of various Tuned Amplifiers. To learn the working of Tuned Amplifiers, we need to understand the qualitative behaviour of passive L , C and R elements. A specific circuit of L and C components, which responds to a specific frequency or a set of frequencies within a narrow passband , is known as parallel resonant circuit Fig.
This circuit is also known as a Tuned Circuit. Assume the impedance of the Tuned circuit as Z p or Z T. Determine the bandwidth.
Tuned Amplifiers use LC circuits. In LC circuits, the charge flows back and forth between the inductor L and the capacitor C , several billion times similar to flywheel effect. The energy oscillates back and forth just like lashing of water between two levels in a water tank. As a result of this effect, LC circuit is also known as a Tank Circuit. The response of an ideal Tuned Amplifier resembles that of a Band Pass Filter , with stop bands on either side as shown in Fig.
But in practical tuned circuits, it is very difficult to achieve such an ideal response with flat top and steep falls. The frequency response of a practical tuned circuit resembles the skirt of a lady, having a narrow passband with fall-offs on either side, centred on a carrier frequency, as shown in Fig. Skirt selectivity has no units. For an ideal Tuned Amplifier, Skirt Selectivity is 1. But achieving such selectivity is not possible.
Skirt Selectivity of 3 or less is preferable in most of the communication applications. Skirt selectivity is measured as the ratio of dB bandwidth S to 3-dB bandwidth B. Demerits of tuned circuits for low-frequency amplification. Resonant frequency of a parallel tuned circuit. For low-frequency signal amplification, values of L and C are large, meaning the inductive and capacitance elements will be bulky and expensive.
So, RC and Transformer-coupled Amplifiers are used for low-frequency applications. Depending upon the type of coupling used in the cascaded Tuned Amplifiers, they can also be classified as follows:. However, the normal classification is based on the type of tuned stages :. Direct- or capacitance-coupled Tuned Amplifier Fig. Output is taken through a coupling-capacitor to load resistance R L or to the input port of a latter amplifying stage.
Typical frequency response of the Amplifier is shown in Fig. Amplifier gain is large, when the input signal matches the resonant frequency, because the impedance of the tuned circuit is high at the resonant frequency. At frequencies other than the resonant frequency, i reactances of the inductor coil and the capacitor no longer balance, ii the impedances are less than those at the resonant frequency f r , and iii hence the voltage gains are reduced to low values.
The Amplifier response has Band Pass Filter characteristic with narrow passband. Thus, inductor L and capacitor C of the tuned circuit decide the frequency response of the Amplifier. Single-Tuned Amplifier works as the simplest band pass Amplifier. One of the functions of resistor R D is to stabilise Amplifier gain. Input signal causes variations in the DC bias to Gate terminal, and varying Gate voltage causes varying Drain current. Varying Drain current flows through the tuned circuit Drain circuit whose impedance varies with frequency.
LC circuit is tuned to input signal frequency, which is resonant frequency of tuned circuit, based on Amplifier design. At resonance, dynamic impedance of tuned circuit is large. Signal current develops maximum output voltage so that the Amplifier shows maximum gain at the selected resonant frequency.
It rejects the signals outside the resonant frequency. The expressions for gain and bandwidth of the Amplifier are derived using the equivalent circuits in Figs. To obtain mathematical expressions for gain and bandwidth of the Amplifier, JFET is also replaced with its equivalent circuit shown in Fig.
Single-tuned FET Amplifier voltage gain is derived by using its simplified equivalent circuit of Fig. Derivation for voltage gain A V of capacitive-coupled tuned amplifier. Equation 5. Magnitude is high at the frequency where the denominator of Eq. At resonant frequency f r centre frequency gain.
Therefore, on simplification of Eq. Frequencies at which function gain is down by 3 dB, from the centre frequency, are called as half-power frequencies. They are determined from the above equations of the previous section. For the Amplifier circuit, assuming input resistance R in and output resistance R out to be equal, equations at half-power frequencies are.
Rearranging the terms in Eq. Two solutions of the above quadratic equation are given below:. Thus, it is known that the product of Amplifier gain and bandwidth is constant. We may express the response in the passband of the narrow band Amplifier by putting. Typical response of single-tuned amplifier is shown in Fig. On similar lines universal resonance curves can also be obtained. Input impedance of FET Amplifier includes negative resistance for frequencies below resonance.
Negative input resistance is due to parasitic capacitance C GD. It acts as a feedback loop from output to input of the Amplifier, in turn causing the Amplifier to be bilateral. Feedback destabilises the Amplifier and forces undesirable oscillations, and in order to cancel the feedback effect, a neutralisation circuit can be added. A second coil is tightly coupled to the inductor, with unity turns ratio, and voltage induced will be opposite in phase to that of AC component.
From above equation,. Signal to be amplified is connected at the input terminals of the transistor. The tank circuit is tuned to the input signal frequency as per design of the Amplifier. At resonant frequency, the tuned circuit has large impedance and so the signal current develops large amplitude, with the signal amplitudes limited to a maximum of supply voltage V CC. Tuning capacitance is C T. Circuit Fig. It has negligible effect on circuit performance.
The equivalent circuit is shown in Fig. R P is the dynamic resistance at resonance for parallel-tuned circuit. The equivalent circuit in Fig. From the final simplified circuit Fig. Gain A is obtained by substituting. Later, we will see the advantages of Tuned Amplifiers in tuning out the parasitic capacitances in the circuit. Another way of obtaining the expression for gain from the equivalent circuit Fig. This gain expression is similar to the gain for single-tuned Amplifier using FET device.
Maximum Amplifier gain occurs at resonance, when the impedance offered by the tuned circuit is at its maximum. Figure Inductive coupling between successive Amplifier stages is common in radio frequency Amplifiers such as IF Amplifiers.
single- stage transistor amplifiers
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Basics of Amplifiers Interview Questions
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Module 2.5
This is also sometimes referred to as single ended power amplifier. In case of a direct-coupled class A power am plifier shown, the quiescent current flows through the collector resistive load a nd causes large wastage of dc power in it. This d c power dissipated in the load resistor does not contribute to the useful ac output power. Furthermore, it is generally inadvisable to pass t he dc through the output device such as in a voice coil of a loudspeaker.
What is Transformer Coupled Amplifier & Its Working
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Power Amplifier.docx
An electronic amplifier , amplifier , or informally amp is an electronic device that increases the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier modulates the output of the power supply. Numerous types of electronic amplifiers are specialized to various applications. An amplifier can refer to anything from a electrical circuit that uses a single active component, to a complete system such as a packaged audio hi-fi amplifier. Amplifiers are described according to their input and output properties. The gain may be specified as the ratio of output voltage to input voltage voltage gain , output power to input power power gain , or some combination of current, voltage, and power. In many cases, with input and output in the same unit, gain is unitless though often expressed in decibels.
Chapter 13 Tuned Amplifiers – Electronic Circuit Analysis
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Amplifier is a circuit that is used for amplifying a signal. The input signal to an amplifier will be a current or voltage and the output will be an amplified version of the input signal. An amplifier circuit which is purely based on a transistor or transistors is called a transistor amplifier. Transistors amplifiers are commonly used in applications like RF radio frequency , audio, OFC optic fibre communication etc. Anyway the most common application we see in our day to day life is the usage of transistor as an audio amplifier.
Post a Comment. Transformer Coupled Amplifier and it's Frequency Response. Transformer — Coupled Amplifier. The main drawback of RC coupled amplifier is low voltage and power gains and poor impedance matching. This is because of the decrease in effective load R AC of each stage. If the effective load resistance of each stage could be increased, the voltage and power gain could be increased. This van be achieved by transformer coupling.
Untuned large signal amplifier power amplifier of class AB and B type invariably use transformer coupled stages while those of class A type also generally use transformer coupled stage. RC coupled stages are not used because the quiescent current flawing through the load resistor results in large wastage of dc power in it. This dc power dissipated in the load resistor does not contribute to the useful ac output power. Further flow of dc current through the output device is not desirable.
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