Engineering Projects

The concept of pulse amplitude modulation (PAM) has been introduced in this article. Still, there are a few specifics regarding the creation of pulse amplitude modulated signal at the output of a sample-and-hold circuit that necessitates discussion. There are two basic sampling techniques used to create a PAM signal. The first is natural sampling. Natural sampling is when the tops of the sampled waveform (the sampled analog input signal) retain their natural shape. An example of natural sampling is shown in figure 1(a). Notice that one side of the analog…

Introduction to Sample-and-Hold Circuit Most analogs to digital converter (A/D) integrated circuits come with sample and hold circuits (S/H) integrated into the system, but it is still necessary for the user to have a good understanding of its operation, including both the capabilities and the limitations of the Sample and hold circuit. A typical S/H circuit is shown in Figure 1. The analog signal is typically inputted into a buffer circuit. The purpose of the buffer circuit is to isolate the input signal from the S/H circuit and to provide…

Delta modulation (DM), sometimes called slope modulation, is another truly digital system (as is PCM). It transmits information to only indicate whether the analog signal it encodes is to “go up” or “go down.” This process is shown in Figure 1. Note that the encoder outputs are highs or lows that “instruct” whether to go up or go down, respectively. The relative simplicity of this system is readily apparent as compared to PCM. Delta modulation takes advantage of the fact that voice signals do not change abruptly and there is…

Digital Signal Encoding Formats: Transmission of digital data using a binary format (+5 V-hi, 0.0 V-low) is usually limited to short distances such as a computer to a printer interface. Typically the binary data are transmitted serially over a single wire, fiber, or RF link. This requires that the binary data be encoded in such a way that highs and lows can easily be detected. The transmission systems typically use a serial transmission system that is either asynchronous or synchronous. This requires the addition of clocking information in the data…

Codes and raw digital data are being transmitted with increasing volume every year. Unless some means of code error detection are used, it is not possible to know when errors have occurred. These errors are caused by noise and transmission system impairments. In contrast, it is obvious when a voice transmission has been impaired by noise or equipment problems. Redundancy is used as the means of error detection when codes and digital data are transmitted. A basic redundancy system is to transmit everything twice and to make sure that an…