AT&T 518-600-016 manual Analog to Digital Signal Processing

ANALOG TO DIGITAL SIGNAL PROCESSING

Analog to Digital Signal Conversion

processor. The port processor directs Touch-Tone circuitry to output tones. The tones are placed on the TDM bus by the DSE through buffer circuitry. After a tip condition occurs at the remote end, a conversation may occur.

The MERLIN II system receives analog signals from the central office lines and analog modules. In order to be switched, the analog signals must be converted to digital signals. Digital transmissions have several advantages over analog transmissions. They produce superior bit error rates and have lower noise/signal degradation, simpler circuitry in some cases, and greater flexibility. They also have various performance advantages, such as speed and a nonblocking architecture.

If an analog signal is sampled in increments equivalent to twice the frequency of that signal, then the sample can faithfully reproduce the signal at a digital level.

The first step in analog to digital conversion is to sample the pulse amplitude of the analog signal. Then the sample is converted into a series of amplitude steps. This technique is referred to as Pulse Amplitude Modulation (PAM). Analog to digital converters (codecs) are an integral part of voice and data systems. Codecs use a variety of encoding techniques. The MERLIN II system uses Pulse Code Modulation (PCM).

The process of converting an analog signal to a digital level increases the capacity and efficiency of data transmissions. However, a digitized analog signal retains some of the problems of older transmission systems, such as having to be amplified.

1-40 Theory of Operation