- Analog and Digital Transmission
- There are a number of differences between analog and digital transmission, and it is important to understand how conversions
- between analog and digital occur. Let's look first at the older form of transmission, analog.
- Analog Transmission
- An analog wave form (or signal) is characterized by being continuously variable along amplitude and frequency. In the
- case of telephony, for instance, when you speak into a handset, there are changes in the air pressure around your mouth.
- Those changes in air pressure fall onto the handset, where they are amplified and then converted into current, or voltage
- fluctuations. Those fluctuations in current are an analog of the actual voice pattern—hence the use of the term analog to describe these signals (see Figure
- Digital Transmission
- Digital transmission has several adv antages over analog transmission:
- 1. Analog circuits require ampliers, and each amplier adds distortion and noise to the
- signal.
- 2. In contrast, digital ampliers regenerate an exact signal, eliminating cumulative
- errors.An incoming (analog) signal is sampled, its v alue is determined, and the node
- then generates a new signal from the bit v alue; the incoming signal is discarded.
- With analog circuits, in termediate nodes amplify the incomiing signal, noise and all.
- 3. V oice, data, video, etc. can all by carried by digital circuits. What about carrying
- digital signals over analog circuit? The modem example shows the diculties in
- carrying digital over analog.
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