Engineering Projects

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…

Two of the most common alphanumeric codes schemes for binary data are ASCII, the American Standard Code for Information Interchange; and EBCDIC, the Extended Binary-Coded Decimal Interchange Code. Each of these codes can be found in many digital systems, with the ASCII code being the most prevalent. Types of Alphanumeric Codes The ASCII Code ASCII is a 7-bit code used for representing alpha-numeric symbols with a distinctive code word. The ASCII code was developed by a committee of the American National Standards Institute (ANSI) for the purpose of coding binary…

Direct Digital Synthesis Direct digital synthesis (DDS) systems became economically feasible in the late 1980s. They offer some advantages over analog synthesizers but generally tend to be somewhat more complex and expensive. They are, however, useful for some applications as will be discussed. The digital logic used can improve on the repeatability and drift problems of analog units that often require select-by-test components. These advantages also apply to digital filters that have replaced some standard analog ones in recent years. The disadvantages of DDS (and digital filters) are the relatively…