Chapter 2 Electronics section 2-3 Analog-Digital Conversion 电气工程及其自动化专业英语课件

Section 3 Analog-Digital Conversion
information content, is not expressed in binary form. In the straightforward sampling of a sine wave, the amplitude is an essential part of the information content. In contrast, the conversion from an analog signal to a digital signal results in a binary number at each sampling point.
Section 3 Analog-Digital Conversion
The precision of analog-to-digital conversion is established by the number of binary bits, which correspond to maximum or full-scale analog value. Four bits allow the quantization in 0 to l5 equal intervals. For the binary representation of the amplitude to change by one bit, an analog amplitude must change by 6.25 percent. A byte (eight bits) allows a precision of 0.4 percent; seven bits of binary code correspond to approximately l percent encoding accuracy.
Section 3 Analog-Digital Conversion
Two important parameters must be considered in selecting a conversion technique or a variation of a conversion technique. One is the precision required in the analog-to-digital conversion; the other is the speed or the time interval allowed for the conversion. These two parameters are essentially incompatible because high-precision and highspeed conversions are difficult to achieve concurrently. High-speed or fast analog-to-digital conversion is a relative term, but in the context of digital computer conversion of binary data from
Section 3 Analog-Digital Conversion
they are equivalent to an ordinary SPDT switch controlled by the binary signal from the register. The switches feed a resistive summing network which converts each bit into its weighted current value and sums them for a total current. This total value is then fed the amplifier, which performs two functions, current to voltage conversion and scaling, so that the output voltage of the D/A converter will be the proper value.
Chapter 2 Electronics
Section 3 Analog-Digital Conversion
are converted or restored to a continuously variable form. The clarity and fidelity of laser-read digital recordings of music and speech and the freedom of these recordings from background noise are recent advancements, but the human ear cannot convert binary data recorded on a disc to music or speech. The electronic conversion of binary data to analog signals is necessary.
Section 3 Analog-Digital Conversion
Digital-to-analog conversion To convert a digital signal to analog, it is
necessary to treat each bit in this weighted manner. A block diagram of such a device is shown in Fig.24. The reference voltage source feeds a precisely regulated voltage to the voltage switches. Upon receipt of a convert signal, binary data is clocked into the register, with each bit assigned a weighted value of current or voltage. These binary signals from the input register next feed voltage switches which provide one of two possible outputs. Thus,
Because many analog-to-digital conversions need not be made quickly, a high degree of precision is possible. The complexity and cost of attaining high precision, however, may modify the goal. The application intended for the conversion of the analog variable may determine what degree of digital precision is required.
Section 3 Analog-Digital Conversion
analog to digital, "high-speed" sampling intervals are about ten computer clock cycles rather than tens of thousands. Conversion in the interval of one microsecond is moderately fast but not limiting.
Some ways of sampling analog signals cannot be considered analog-to-digital conversion because the amplitude of the signal, an important aspect of the
The transducer is the name of the device that produces a voltage or a current proportional to the physical phenomenon to which it responds. A temperature transducer, for example, can generate a voltage related to the temperature. In some cases
Section 3 Analog-Digital Conversion
Fig.2-4 Block diagram of digital to analog converter
Section 3 Analog-Digital Conversion
The input register is a parallel-in, parallel-out device. The converter signal is used to clock the input data into the register where it is stored until the next converter signal is received.
Section 3 Analog-Digital Conversion
the voltage is derived from the sensitive element in an electrical circuit, as when a temperature sensitive resistor and a constant resistance form a voltage divider whose voltage is related directly to the temperature. Some transducers generate voltages directly, such as photoelectric elements and piezoelectric devices. Many voltage sources require voltage amplification to facilitate conversion from their analog values to binary numbers.
Section 3 Analog-Digital Conversion
Analog-to-digital conversion Only two basic techniques exist for analog-to-
digital conversion (ADC). One is to compare the analog voltLeabharlann Baiduge amplitude to a binary voltage scale in which the match yield the binary number that corresponds to the amplitude. The other technique is to integrate the analog signal and to use the measured time (a given number of clock pulses) for the amplitude of the integral to reach a value to establish an equivalent binary number. Each of the systems discussed below uses one or the other of these techniques.