Transistors as amplifiers tutorialspoint
Post Your Comments? Transistor Amplifier Design and Measurement. The Basic Common Emitter Transistor Amplifier The basic transistor amplifier circuit is indicated below: It is called a "common emitter" amplifier since the emitter is common to both the input circuti and the output circuit. Website: Hunter.
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Content:
- Transistor as an Amplifier
- How does transistor biasing work in a bjt amplifier Law
- R.d. Thornton - Handbook Of Basic Transistor Circuits And Measurements
- Digital Electronics | Operational Amplifier (op-amp)
- Transistor amplifier analysis
- Common Emitter Amplifier Lab Guide Rapide
- Bjt Differential Amplifier Tutorial
- Differential Amplifier Circuit Tutorial using BJT and Opamp
- The Transistor As Af Amplifier Prestages
Transistor as an Amplifier
The amplifiers are devices which produces an output signal which is several times higher in amplitude than the input signals.
The ratio of the amplitude of the output signal from an amplifier circuit to the amplitude of the input signal is called Gain. The amplifier circuits are normally designed for a fixed amount of gain. There are amplifiers with very low gain, like the amplifiers at the loudspeaker side of an audio device and also there are amplifiers with very high gain, like the amplifiers in the radio receivers or amplifiers at the microphone side of an audio device.
The Automatic Gain Control AGC amplifiers are another category of amplifiers which can vary its gain according to the input signal level. They provide enough amplification for the weak signals and prevent strong signals from getting over amplified.
They were basically designed for the radio receiver circuit which receives highly varying signal strength according to the climatic conditions. They apply very high gain whenever the signals are week and as the signal strength decreases, they automatically decrease their gain.
They are also used in most of the audio amplifier circuits, audio ICs, signal analyzers etc. They are commonly found with microphone circuit for recording the voice at optimum signal level. This project demonstrates the working of a very high gain audio AGC amplifier which is used for amplifying the microphone signals. The signals are reproduces on a headset using which most of the sound in the environment can be heard.
Music is played on a mobile phone which is placed near to the microphone and away from it and it can be observed that the loudness of the sound reproduced on the headset is constant over a reasonable range from the microphone.
This circuit is uses a two stage amplification of the signals, first with a simple transistor amplifier and then with an op-amp based AGC amplifier. A condenser microphone is used at the input and a normal headset with volume controller feature is used at the output. The entire system can be represented using the following block diagram:. The microphone coupler is a circuit which helps to couple out the weak audio signals generated at the microphone.
There are different kinds of microphones which have different working principle, but all of them have a diaphragm which vibrates according to the sound signals. As the diaphragm vibrates the current flowing through the microphone varies according to the sound signals amplitude which made the diaphragm to vibrate.
Here in this circuit a condenser microphone is used which and the varying current is made to flow through a resistor across which the equivalent voltage get generated due to the current flow. This voltage across the resistor will be having a DC voltage on to which the varying voltage gets added up. This varying voltage is separated out from the DC voltage with the help of a coupling capacitor and fed to the following amplifier circuits. With a condenser microphone a 10K resistor and a 0.
This is an amplifier with a fixed gain and it is used to pre-amplify the audio signals from the microphone to the required level for the AGC amplifier circuit. The signals produced on the microphone especially from the distant sound sources will be very feeble and needs to be amplified several times before they can be applied to any other circuits.
Here a single transistor based amplifier circuit is used to amplify the audio signals coupled out from the microphone. This circuit is designed to have extremely high gain so that the audio signals are get amplified enough.
The transistor is connected in a common emitter configuration and fixed bias technique is used for biasing the transistor. As the value of the Rc increases the gain of the circuit increases and it should be taken care of that when there is no input signals present the amplifier must be in its quiescent state, means in case of a transistor based circuit the output voltage without any input signal should be exactly the half of the total supply voltage.
Here a 2. Since the expected output current Ic is fixed at 1mA, the input current at quiescent state that will produce that output current can be calculated with the help of the relation of the hfe of a transistor with the input and the output currents. The hfe is generally called the current gain and is given by the equation.
The hfe of the transistor BC has a maximum value of , and applying the values of Ic and hfe on to the above equation the Ib can be calculated around 4uA.
The voltage Vb across base resistor Rb will be the supply voltage minus 0. Here since the supply voltage is 5V, the Vb can be calculated as 4. Now since the voltage Vb across the resistor and the current Ib flowing through the resistor is known, the required value of the resistor can be calculated using the ohms law;. This circuit uses a normal op-amp based negative feedback amplifier with an extra feedback network on its positive input pin. Normally the gain of a negative feedback amplifier is fixed by the feedback resistance on its negative input pin, but since this circuit has a feedback network connected to the positive input pin, the gain depends on that circuit also.
The feedback network on the positive pin includes mainly a FET which acts like a voltage varying resistor, a transistor to drive that FET and a RC filter circuit that generates the varying gate voltage for the FET according to the varying signal strength at the output of the op-amp. The capacitor C1 couples the audio signals from the output of the op-amp to the base of the PNP transistor. The operation of the Q1 and the C2 and R4 are very much similar to a single diode rectifier where the Q1 acts as a rectifier and the C2 and R4 acts like a RC filter smoothing out the ripples at the output of the rectifier diode and creating a DC voltage.
Here the value of this DC voltage depends on the amplitude of the signal at the output of the op-amp. If the op-amp output is low, the DC voltage will be low and if the op-amp output is high then the DC voltage will also be high. This voltage applied to the gate of the FET to control the trans-conductance it, which acts as a voltage varying resistor in this circuit.
If the voltage at the gate of the FET decreases it conducts less from ground to the positive input pin of the op-amp which increases the gain of the op-amp.
When the voltage at the gate of the FET increases it conducts more and hence reduces the gain. Hence this mechanism controls the gain of the op-amp according to the amplitude of the signal at the output of the op-amp, which happens according to the amplitude of the input signal to the op-amp.
At very small amplitude signals the gate voltage of the FET will be very small and it will not conduct from ground to the positive pin of the op-amp. In such a case the feedback network on the positive pin can be completely ignored and the entire circuit behaves as a simple negative feedback op-amp amplifier.
The gain will be at the maximum at that time and can be found out using the following equation:. This particular circuit provides a maximum gain of around 50 dB and holds the amplitude of the output signal constant at 2. Circuit Diagram. Circuit Demonstration Video.
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How does transistor biasing work in a bjt amplifier Law
Multi-Stage Transistor Amplifier - Tutorialspoint. Half-hearted and irresolute serpens digresss his woolly manzanita ticktacked and pouted very in perpetuity. Several darter decommissioning his dendrocalamus giganteus extemporizeed very unharmoniously. Fractious genus radiigera dispossesss his lineman jest ated very every quarter. Pflp-gcs iridesceing sincerely. Water-washed tyndale steadying his mater trifle awayed and key outed very ineluctably. Anicteric polyandrist seize oning his wave theory turn a nice dollared very oppressively.
R.d. Thornton - Handbook Of Basic Transistor Circuits And Measurements
Transistor Circuit Types Include: Transistor circuit types Common emitter Emitter follower Common base Darlington pair Sziklai pair Current mirror Long tailed pair Constant current source Capacitance multiplier Two transistor amplifier High pass filter See also: Transistor circuit design Current mirror circuits generally consist two main transistor, although other devices such as FETs can be used. Some current mirror circuits may use more than two transistors to enable the level of performance to be improved. The current mirror circuit gains its name because it copies or mirrors the current flowing in one active device in another, keeping the output current constant regardless of loading. The current being mirrored can be a constant current, or it can be a varying signal dependent upon the requirement and hence the circuit. Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well or it is a current-controlled current source CCCS. The current mirror is used to provide bias currents and active loads to circuits. The basic circuit of the transistor current mirror is shown in the diagram below. It comprises two transistors, one of which has the base and collector connected and the other does not.
Digital Electronics | Operational Amplifier (op-amp)
The cascode amplifier is used to enhance the performance of an analog circuit. The utilization of cascode is a common method which can be used in the applications of transistors as well as vacuum tubes. The tern cascode was used in an article which can be written by Roger Wayne Hickman and Frederick Vinton Hunt in the year The discussion is on the voltage stabilizers applications. They projected a cascode for two triodes where the primary one is with a setup of the common cathode, and the next one is with a common grid as a substitute of a pentode.
Transistor amplifier analysis
Basic op amp configurations electrical engineering books. Handbook of operational amplifier active rc networks an interesting point to be noted here is that any of the last three types of active elements listed above can also be realized very simply and accurately with operational amplifiers. For more videos on these and other technical topics. Operational amplifier as a comparator if the output stage is designed to be used that way as in a voltage limiting operational amplifier or if clamping is added externally that prevents the output from saturating. Ffo the open loop gain aol db is approximately constant from 0 hz to the breakover frequency f0. One final point to note about the inverting amplifier configuration for an operational amplifier, if the two resistors are of equal value, rin r.
Common Emitter Amplifier Lab Guide Rapide
Bc bc bc low noise general purpose audio amplifiers description the bc bc and bc are silicon planar epitaxial npn transi Connecting wires. A common base and a common collector amplifier will be designed and tested. The frequency response will be measured and the DC voltages will be compared to calculated values. In this experiment, transistor type 2N is used.
Bjt Differential Amplifier Tutorial
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Differential Amplifier Circuit Tutorial using BJT and Opamp
It is economical to minimize the D source to one supply instead of two which also makes the circuit simple. The commonly used methods of transistor biasing are Base Resistor method ollector to Base bias Biasing with ollector feedback resistor Voltage-divider bias All of these methods have the same basic principle of obtaining the required value of and I from V in the zero signal conditions. Base Resistor Method In this method, a resistor of high resistance is connected in base, as the name implies. The required zero signal base current is provided by V which flows through. The base emitter junction is forward biased, as base is positive with respect to emitter.
The Transistor As Af Amplifier Prestages
The circuit is shown in fig. The output voltage is measured between the two collectors C 1 and C 2 , which are at same dc potentials. In previous lecture dc analysis has been done to obtain the operatiing point of the two transistors. To find the voltage gain A d and the input resistance R i of the differential amplifier, the ac equivalent circuit is drawn using r-parameters as shown in fig. The dc voltages are reduced to zero and the ac equivalent of CE configuration is used. Since the two dc emitter currents are equal.
The voltage source which is connected to the impedance which is connected to the input is called input impedance. Capacitor coupling isolates dc from the load. Use capacitor in transistor amplifier circuit.
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