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The main disadvantage of this coupling method is that it causes some loss for the low frequency signals. However, for amplifying signals of frequencies greater than 10 Hz, this coupling is the best and least expensive method. It is usually applied in small signal amplifiers, such as in record players, tape recorders, radio receivers, etc.
Coupling can be deliberate as part of the function of the circuit, or it may be undesirable, for instance due to coupling to stray fields. For example, energy is transferred from a power source to an electrical load by means of conductive coupling , which may be either resistive or direct coupling .
A direct-coupled amplifier [1] or DC amplifier is a type of amplifier in which the output of one stage of the amplifier is coupled to the input of the next stage in such a way as to permit signals with zero frequency, also referred to as direct current, to pass from input to output. This is an application of the more general direct coupling.
Output transformerless (OTL) is a type of vacuum tube audio power amplifier, which omits an output transformer for the purpose of greater linearity and fidelity. Conventional vacuum tube amplifier designs rely upon an output transformer to couple the amplifier's output stage to the loudspeaker.
Transformer coupling is an alternative AC coupling. Like RC coupling, it isolates DC between stages. However, transformers are bulkier and much more expensive than capacitors so is used less often. Transformer coupling comes into its own in tuned amplifiers. The inductance of the transformer windings serves as the inductor of an LC tuned circuit.
Conversely, a voltage follower inserted between a small load resistance and a driving stage presents a large load to the driving stage—an advantage in coupling a voltage signal to a small load. This configuration is commonly used in the output stages of class-B and class-AB amplifiers. The base circuit is modified to operate the transistor in ...
Designs frequently use a coupling greater than this (over-coupling) in order to achieve an even wider bandwidth at the expense of a small loss of gain in the centre of the passband. Cascading multiple stages of double-tuned amplifiers results in a reduction of the bandwidth of the overall amplifier. Two stages of double-tuned amplifier have 80% ...
Here the internal units or portions of the op-amp (like the input stage, voltage gain stage, and output stage) will be direct coupled and will also be used to set up the bias conditions inside the op-amp (the input stage will also supply the input bias to the voltage gain stage, for example).