Single Amplifier

A digital signal uses discrete (discontinuous) values. By contrast, non-digital (or analog) systems use a continuous range of values to represent information. The information represented can be either discrete, such as numbers or letters, or continuous, such as sounds, images, and other measurements of continuous systems.

Digital information has certain properties that distinguish it from analog communication methods. These include:

1. Synchronization. Digital communication uses specific synchronization sequences for determining synchronization.
2. Language. Digital communications requires a language, which should be possessed by both sender and receiver and should specify meaning of symbol sequences.
3. Errors. Disturbances in analog communication causes errors in actual intended communication but disturbances in digital communication does not cause errors enabling error free communication
4. Analog communication copies are quality wise not as good as their originals while due to error free digital communication, copies can be made indefinitely.
5. Granularity. for a continuously variable analog value to be represented in digital form there occur quantization error which is difference in actual analog value and digital representation and this property of digital communication is known as granularity.

Many devices come with built in translation facilities from analog to digital. Microphones and speaker are perfect examples of analog devices. Analog technology is cheaper but there is a limitation of size of data that can be transmitted at a given time.

Digital technology has revolutionized the way most of the equipment’s work. Data is converted into binary code and then reassembled back into original form at reception point. it offers a wider range of options. Digital equipment is more expensive than analog equipment.

Digital devices translate and reassemble data and in the process are more prone to loss of quality as compared to analog devices. Computer advancement has enabled use of error detection and error correction techniques to remove disturbances artificially from digital signals and improve quality

Digital technology has been most efficient in cellular phone industry. Analog phones have become redundant even though sound clarity and quality was good.

Analog technology comprises of natural signals like human speech. With digital technology, this human speech can be saved and stored in a computer. Thus, digital technology opens up the horizon for endless possible uses.

Single-stage amplifier have only one amplifying device. It consists of amplification stage that includes a transistor. The transistor is connected to a load resistor through which a load current flows. The value of the load resistor together with the trans conductance value affects the amplifier‘s voltage gain.

Single-stage amplifiers include:

1. Common-emitter (CE) amplifier
2. Common-collector (CC) amplifier
3. Common-base (CB) amplifier

It is called the common-emitter configuration because (ignoring the power supply battery) both the signal source and the load share the emitter lead as a common connection point

Common-emitter amplifier: The input and output signals both share a connection to the emitter

Before, a small solar cell current saturated a transistor, illuminating a lamp. Knowing now that transistors are able to “throttle” their collector currents according to the amount of base current supplied by an input signal source, we should see that the brightness of the lamp in this circuit is controllable by the solar cell’s light exposure.

When there is just a little light shone on the solar cell, the lamp will glow dimly. The lamp’s brightness will steadily increase as more light falls on the solar cell.

It is called the common-collector configuration because (ignoring the power supply battery) both the signal source and the load share the collector lead as a common connection point

Common collector: Input is applied to base and collector. Output is from emitter-collector circuit.

It should be apparent that the load resistor in the common-collector amplifier circuit receives both the base and collector currents, being placed in series with the emitter. Since the emitter lead of a transistor is the one handling the most current (the sum of base and collector currents, since base and collector currents always mesh together to form the emitter current), it would be reasonable to presume that this amplifier will have a very large current gain. This presumption is indeed correct:

the current gain for a common-collector amplifier is quite large, larger than any other transistor amplifier configuration

It is called the common-base configuration because (DC power source aside), the signal source and the load share the base of the transistor as a common connection point shown in. Common-base amplifier: Input between emitter and base, output between collector and base.

Common-base amplifier: Input between emitter and base, output between collector and base.

Perhaps the most striking characteristic of this configuration is that the input signal source must carry the full emitter current of the transistor, as indicated by the heavy arrows in the first illustration. As we know, the emitter current is greater than any other current in the transistor, being the sum of base and collector currents.

In the last two amplifier configurations, the signal source was connected to the base lead of the transistor, thus handling the least current possible.