Amplifier Coupling
To obtain greater amplification, transistor amplifiers may be connected together. However, to prevent one amplifier’s bias voltage from affecting the operation of the second amplifier, a coupling technique must be used. The coupling method used must not disrupt the operation of either circuit. Coupling methods used include resistance-capacitance coupling, impedance coupling, transformer coupling, and direct coupling.
Resistive-capacitive coupling, or RC coupling, consists of two resistors and a capacitor connected as shown in Figure 37-17. Resistor R3 is the collector load resistor of the first stage. Capacitor C1 is the DC-blocking and AC-coupling capacitor. Resistors R5 and R6 are the input load resistor and DC return resistor for the base-emitter junction of the second stage. Resistance-capacitive coupling is used primarily in audio amplifiers.
Coupling capacitor C1 must have a low reactance to minimize low-frequency attenuation. Typically, a high-capacitance value of 10 to 100 microfarads is used. The coupling capacitor is generally an electro- lytic type.
The reactance of the coupling capacitor increases as the frequency decreases. The low-frequency limit is determined by the size of the coupling capacitor. The type of transistor used determines the high-frequency limit.
The impedance-coupling method is similar to the RC-coupling method, but an inductor is used in place of the collector load resistor for the first stage of amplification (Figure 37-18).
Impedance coupling works just like RC coupling. The advantage is that the inductor has a very low DC resistance across its windings. The AC output signal is developed across the inductor just as across the load resistor. However, the inductor consumes less power than the resistor, increasing the overall efficiency of the circuit.
The disadvantage of impedance coupling is that the inductance reactance increases with the frequency. The voltage gain varies with the frequency. This type of coupling is ideal for single-frequency amplification when a very narrow band of frequencies must be amplified.
In a t ransfor mer-couple d circuit, t he two amplifier stages are coupled through the transformer (Figure 37-19). The transformer can effectively match a high-impedance source to a low-impedance load. The disadvantage is that transformers are large and expensive. Also, like the inductor-coupled amplifier, the transformer-coupled amplifier is useful only for a narrow band of frequencies.
When very low frequencies or a DC signal must be amplified, the direct-coupling technique must be used (Figure 37-20). Direct-coupled amplifiers provide a uniform current or voltage gain over a wide range of frequencies. This type of amplifier can amplify frequencies from 0 (DC) hertz to many thousands of
hertz. However, direct-coupled amplifiers find their best applications with low frequencies.
A drawback of direct-coupled amplifiers is that they are not stable. Any change in the output current of the first stage is amplified by the second stage. This occurs because the second stage is essentially biased by the first stage. To improve the stability requires the use of expensive precision components.
Questions
1. What are the four methods for coupling amplifiers?
2. Where would RC coupling be used?
3. What determines low-frequency and high- frequency coupling?
4. Why would impedance coupling be used over RC coupling?
5. What is the drawback of using direct-coupled amplifiers?
Related posts:
Incoming search terms:
- amplifier coupling
- reasons for amplifier coupling
- what is amplifier coupling
- amplifier coupling methods
- impedance coupling amplifier
- coupling methods in amplifier
- methods of coupling amplifiers
- methods of coupling amplifier
- coupling in amplifiers
- what is coupling in amplifiers
- what is the need of coupling in amplifier
- types of amplifier coupling
- impedance coupling
- Amplifier on the basics of coupling
- types of coupling method
- transistor coupling methods
- rf amplifier coupling
- transistor amplifier coupling methods
- coupling amplifier
- what is the use of coupling in amplifier
- impedance coupling in amplifier
- methods of coupling am
- lc coupling amplifiers
- list 3 advantage and disadvantage of direct coupling
- list any two types of coupling used in amplifiers
- list methods of coupling amplifier
- list methods used for amplifier coupling
- Method of amplifier coupling
- method of coupling amplifier
- Method of coupling amplifire
- methodology of an rc coupled amplifier
- methods of amplifier coupling
- coupling methodo of amplifier
- Amplifier cou
- basic method of coupli
- basic qstn from coupling method of amplifier
- couplimg in amplifiet
- coupling am
- Coupling ampl
- why coupling in amplifier
- Coupling methods
- coupling methods in am
- COUPLING METHODS USED IN AMPLIFIERS
- coupling of ampli
- coupling of amplifiers
- coupling techniques of amplifier
- describe three methods of coupling high frequency circuit
- Explain 3 types of transistor amplifier coupling method
- explain the amplifier coupling techniques in electronics
- explain the coupling methods from the amplified stage in am