Tag: Free Book Digital

14.4 Electrical Signal Types
With BogusBus, our signals were very simple and straightforward: each signal wire (1 through 5) carried a single bit of digital data, 0 Volts representing “off” and 24 Volts DC representing “on.” Because all the bits arrived at their destination simultaneously, we would call BogusBus a parallel network technology. If we were to improve the…

14.3 Data Flow
Buses and networks are designed to allow communication to occur between individual devices that are interconnected. The flow of information, or data, between nodes, can take a variety of forms: With simplex communication, all data flow is unidirectional: from the designated transmitter to the designated receiver. BogusBus is an example of simplex communication, where the…

14.2 Networks and Busses
This collection of wires that I keep referring to between the tank and the monitoring location can be called a bus or a network. The distinction between these two terms is more semantic than technical, and the two may be used interchangeably for all practical purposes. In my experience, the term “bus” is usually used…

14.1 Introduction to Digital Communication
In the design of large and complex digital systems, it is often necessary to have one device communicate digital information to and from other devices. One advantage of digital information is that it tends to be far more resistant to transmitted and interpreted errors than information symbolized in an analog medium. This accounts for the…

13.10 Practical Considerations of ADC Circuits
Perhaps the most important consideration of an ADC is its resolution. Resolution is the number of binary bits output by the converter. Because ADC circuits take in an analog signal, which is continuously variable, and resolve it into one of many discrete steps, it is important to know how many of these steps there are…

13.9 DeltaSigma ADC
One of the more advanced ADC technologies is the socalled deltasigma, or ΔΣ (using the proper Greek letter notation). In mathematics and physics, the capital Greek letter delta (Δ) represents difference or change, while the capital letter sigma (Σ) represents summation: the adding of multiple terms together. Sometimes this converter is referred to by the…

13.8 Slope (integrating) ADC
So far, we’ve only been able to escape the sheer volume of components in the flash converter by using a DAC as part of our ADC circuitry. However, this is not our only option. It is possible to avoid using a DAC if we substitute an analog ramping circuit and a digital counter with precise…

13.7 Tracking ADC
A third variation on the counterDACbased converter theme is, in my estimation, the most elegant. Instead of a regular “up” counter driving the DAC, this circuit uses an up/down counter. The counter is continuously clocked, and the up/down control line is driven by the output of the comparator. So, when the analog input signal exceeds…

13.6 Successive Approximation ADC
One method of addressing the digital ramp ADC’s shortcomings is the socalled successiveapproximation ADC. The only change in this design is a very special counter circuit known as a successiveapproximation register. Instead of counting up in binary sequence, this register counts by trying all values of bits starting with the mostsignificant bit and finishing at…

13.5 Digital Ramp ADC
Also known as the stairstepramp, or simply counter A/D converter, this is also fairly easy to understand but unfortunately suffers from several limitations. The basic idea is to connect the output of a freerunning binary counter to the input of a DAC, then compare the analog output of the DAC with the analog input signal…

13.4 Flash ADC
Also called the parallel A/D converter, this circuit is the simplest to understand. It is formed of a series of comparators, each one comparing the input signal to a unique reference voltage. The comparator outputs connect to the inputs of a priority encoder circuit, which then produces a binary output. The following illustration shows a…

13.3 The R/2R DAC (DigitaltoAnalog Converter)
The R/2R DAC circuit is an alternative to the binaryweightedinput (R/2nR) DAC which uses fewer unique resistor values. R/2R DAC vs. R/2nR DAC A disadvantage of the former DAC design was its requirement of several different precise input resistor values: one unique value per binary input bit. Manufacture may be simplified if there are fewer…

13.2 The R/2nR DAC: BinaryWeightedInput DigitaltoAnalog Converter
What Is a R/2nR DAC Circuit? The R/2nR DAC circuit, otherwise known as the binaryweightedinput DAC, is a variation on the inverting summing opamp circuit. (Note that “summing” circuits are sometimes also referred to as “summer” circuits.) If you recall, the classic inverting summing circuit is an operational amplifier using negative feedback for controlled gain, with…

13.1 Introduction to DigitalAnalog Conversion
Connecting digital circuitry to sensor devices is simple if the sensor devices are inherently digital themselves. Switches, relays, and encoders are easily interfaced with gate circuits due to the on/off nature of their signals. However, when analog devices are involved, interfacing becomes much more complex. What is needed is a way to electronically translate analog…

12.6 Ring Counters
If the output of a shift register is fed back to the input. a ring counter results. The data pattern contained within the shift register will recirculate as long as clock pulses are applied. For example, the data pattern will repeat every four clock pulses in the figure below. However, we must load a data…