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Emitter follower amplifier gain adjustment

The way that the input enters the system and the output leaves it is very important and affects the general behavior of an amplifier. In more technical terms, the flow of current of both the input and output is controlled by the input and output impedance of the amplifier. The second section highlights the several reasons of importance of choosing appropriate values for these parameters. First of all, it is important to realize for the understanding of this tutorial that the input and output impedances are a concept and do not represent any physical resistor that can be removed or changed. We will detail later on these different connection arrangements.


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Emitter follower amplifier gain adjustment

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WATCH RELATED VIDEO: Emitter-Follower Configuration (Part 1)

Matching and tuning audio amplifier output stability and sound performance.


Three versions of the most common type of output stage are shown in Figure 5. I have deliberately called this an Emitter-Follower EF rather than a Darlington configuration, as this latter implies an integrated device that includes driver, output, and assorted emitter resistors in one ill-conceived package. As for all the circuitry here, the component values are representative of real practice.

Important attributes of this topology are:. The bias generator must attempt to compensate for both at once, though it can only be thermally-coupled to one. The output devices have substantial thermal inertia, and so any thermal compensation can only be a time-average of the preceding conditions.

Figure 5. The Type II configuration in Figure 5. The shared driver emitter-resistor Rd, with no output-rail connection, allows the drivers to reverse-bias the base-emitter junction of the output device being turned off.

Assume that the output voltage is heading downwards through the crossover region; the current through Re1 has dropped to zero, but that through Re2 is increasing, giving a voltage-drop across it, so TR4 base is caused to go more negative to get the output to the right voltage. This negative excursion is coupled to TR3 base through Rd, and with the values shown can reverse bias it by up to —0.

The speed-up capacitor Cs markedly improves this action, preventing the charge-suckout rate being limited by the resistance of Rd. While the Type I circuit has a similar voltage drop across Re2, the connection of the mid-point of R1, R2 to the output rail prevents this from reaching TR3 base; instead TR1 base is reverse-biased as the output moves negative, and since charge-storage in the drivers is usually not a problem, this does little good.

In Type II the drivers are never reverse-biased, though they do turn off. The important issue of output turn-off and switching distortion is further examined on page It is a common misconception [6] that Class-A drivers somehow maintain better low-frequency control over the output devices, but I have yet to locate any advantage myself. The driver dissipation is of course.

Type III is equally good as Type II at reverse-biasing the output bases, and may give even cleaner HF turn-off as the carriers are being swept from the bases by a higher resistance terminated in a higher voltage, approximating constant-current drive; this remains to be determined by experiment. The large-signal linearity of these three versions is virtually identical — all have the same feature of two base-emitter junctions in series between input and load.

Note that the crossover region appears as a relatively smooth wobble rather than a jagged shape. Another major feature is the gain-droop at high output voltages and low loads, and this gives us a clue that high collector currents are the fundamental cause of this.

A close-up of the crossover region gain for 8! There seems to be only one popular configuration, though versions with gain are possible. The drivers are now placed so that they compare the output voltage with that at the input.

The CFP topology is generally considered to show better thermal stability than the EF, because the Vbe of the output devices is inside the local NFB loop, and only the driver Vbe affects the quiescent conditions.

The true situation is rather more complex, and is explored in Chapter In the CFP output, like the EF, the drivers are conducting whenever the outputs are, so special arrangements to keep them in Class-A seem pointless. The CFP stage, like EF Type I, can only reverse-bias the driver bases, and not the output bases, unless extra voltage rails outside the main ones are provided. The output gain plot is shown in Figure 5. Table 5. See Table 5. Given also the greater quiescent stability, it is hard to see why this topology is not more popular.

When under-biased, this shows up on the distortion residual as narrower spikes than an emitter-follower output gives. The bad effects of gmdoubling as Vbias increases above optimal here 1.

Audio Power Amp Design Handbook. Audio Power Amplifier Design Handbook The emitter-follower output Three versions of the most common type of output stage are shown in Figure 5. Audio Power Amplifier Design Handbook substantially increased, and nothing seems to be gained at LF as far as the output transistors are concerned, for in both Type I and Type II the drivers are still conducting at the moment the outputs turn off, and are back in conduction before the outputs turn on, which would seem to be all that matters.

The output stage I Table 5.


Electronic devices: BJT Amplifiers [part 3]

To investigate the simple NPN emitter follower amplifier also sometimes referred to as the common collector configuration. The breadboard connections are shown in the diagram below. The output of the arbitrary waveform generator, W1, is connected to the base terminal of Q 1. The collector terminal is connected to the positive Vp supply. The emitter terminal is connected to both the 2. The other end of the load resistor is connected to the negative Vn supply.

Common Collector Configuration-Emitter Follower (using Darlington pair)-Gain and input impedance measurement of the circuit. 7. Power Amplifiers-Push pull.

Design of a 2 GHz Linear-in-dB Variable-Gain Amplifier with 80-dB Gain Range


A buffer amplifier sometimes simply called a buffer is one that provides electrical impedance transformation from one circuit to another, with the aim of preventing the signal source from being affected by whatever currents or voltages, for a current buffer that the load may produce. The signal is 'buffered from' load currents. Two main types of buffer exist: the voltage buffer and the current buffer. A voltage buffer amplifier is used to transfer a voltage from a first circuit, having a high output impedance level, to a second circuit with a low input impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interfering with its desired operation. In the ideal voltage buffer in the diagram, the input resistance is infinite and the output resistance zero output impedance of an ideal voltage source is zero. Other properties of the ideal buffer are: perfect linearity, regardless of signal amplitudes; and instant output response, regardless of the speed of the input signal. If the voltage is transferred unchanged the voltage gain A v is 1 , the amplifier is a unity gain buffer ; also known as a voltage follower because the output voltage follows or tracks the input voltage. Although the voltage gain of a voltage buffer amplifier may be approximately unity, it usually provides considerable current gain and thus power gain. However, it is commonplace to say that it has a gain of 1 or the equivalent 0 dB , referring to the voltage gain.

Measuring emitter followers and other transistor configurations

emitter follower amplifier gain adjustment

Expiration termination date : Granted publication date : A kind of non-linear tansfer function generator of for example realizing luminance signal " white stretch ". Wherein, the input parallel coupled of the first and second emitter follower amplifiers ,, output is through first resistance, series coupled of voltage divider. Second resistance of voltage divider is coupled to reference potential point

Transistor Circuit Design Tutorial Includes: Transistor circuit design Circuit configurations Common emitter Common emitter circuit design Emitter follower Common base See also: Transistor circuit types The common emitter transistor amplifier circuit is one of the mainstay circuits for use within electronic circuit design offering many advantages. The common emitter circuit configuration is used in many areas of electronic circuit design: as an audio amplifier, as a basic switch for logic circuits, as a general analogue amplifier and in many other applications.

Op-amp Tutorial 4 : voltage follower, loudness & level indicator, comparato


Voltage follower is generally used for amplify the current of a signal keeping the voltage same incase of driving high output loads low resistance circuits. Op amp as a Simple Microphone amplifier. Input voltages are applied on both the inverting and non-inverting inputs. So far we have seen some basic circuits using op-amp and I suggest the reader to go through the topics thoroughly. Practise as many circuits as possible. With each circuit you make you learn a new thing about the op-amp and your knowledge becomes more solid.

Transistor Common Emitter Amplifier

An audio preamplifier is to be developed for use in a small portable public address PA system. The preamplifier will have a microphone input, and its output will drive a power amplifier to be developed in Section 7. The dc supply voltages are provided by a battery pack or by an electronic power supply. A 2-stage audio voltage preamplifier is shown in FIG. The first stage is a common emitter pnp with voltage-divider bias, and the second stage is a common-emitter npn with voltage-divider bias.

follower power amplifiers (VOUT ≈ VIN − for an emitter follower and variable resistor is adjusted to a bigger resistance, the voltage gain on.

OP-AMP COOKBOOK — Part 2

This installment looks at practical ways of using such op-amps in linear amplifier and active filter applications. The voltage gain and input impedance are determined by the R1 and R2 values, and can be altered to suit individual needs. The gain can be made variable — if required — by using a series combination of a fixed and a variable resistor in place of R2. For optimum biasing stability, R3 should have a value equal to the parallel values of R1 and R2.

Amplifiers are used to increase the voltage and current of a weak signal to desired level. There are two types of amplifiers. They are given below. If you increase the current of DC signal,then the voltage will drop.

Three versions of the most common type of output stage are shown in Figure 5.

Effective date : Year of fee payment : 4. Year of fee payment : 8. Year of fee payment : A variable gain feedback amplifier circuit comprising a degenerated common emitter circuit coupled to an emitter follower circuit, an output of the emitter follower circuit being coupled to an input of the degenerated common emitter circuit via a variable feedback impedance. An automatic gain controller is coupled to the variable feedback impedance in order to reduce a closed loop gain of the variable gain feedback amplifier circuit when required.

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  1. Kantit

    Useful thing

  2. Tomeo

    You've got a great thought