Introduction to digital circuits

Engineers generally classify electronic circuits as being either analog or digital in nature.

Whether or not a device is digital depends upon

1. Does it have an alphanumeric (shows letters and numbers) display?
2. Does it have a memory or can it store information?
3. Can the device the programmed?

If the answer to any one of the three questions is yes, then the product probably contains digital circuitry.

Advantages of digital over analog circuits
1. Generally, digital circuits are easier to design using modem integrated circuits (ICs).
2. Information storage is easy to implement with digital.
3. Devices can be made programmable with digital.
4. More accuracy and precision is possible.
5. Digital circuitry is less affected by unwanted electrical interference called noise.

A signal can be defined as useful information transmitted within, to, or from electronics circuits. Signals are commonly represented as a voltage varying with time. However, a signal could be an electrical current that either vanes continuously (analog) or has an on-off characteristic (digital). An analog device is one that has a signal which varies continuously in step with the input. A digital device operates with a digital signal. The digital signal is only at +5 V or at 0 V. The HIGH voltage is ±5 V or commonly called logical 1; the LOW voltage is 0 V or commonly called logical 0. Circuits that handle only HIGH and LOW signals are called digital circuits. An analog signal assumes a continuous range of values: A digital signal assumes discrete (isolated, separate) values as there are two permitted values

Digital signals are composed of two well- defined voltage levels. Most of the voltage levels used in this class will be about +3 V to +5 V for HIGH and near 0 V (GND) for LOW. These are commonly called TTL voltage levels because they are used with the transistor- transistor logic family of ICs. Logic levels are different for various digital logic families, such as TTL and CMOS. These logic levels are commonly referred to as HIGH. LOW, and undefined.

Limitations of digital circuits

1. Most ‘real-world” events are analog in nature.
2. Analog processing is usually simpler and faster.

Digital circuits are appearing in more and more products primarily because of low-cost, reliable digital lCs. Other reasons for their growing popularity are accuracy, added stability, computer compatibility, memory, ease of use, simplicity of design and compatibility with alphanumeri displays.

Example of digital and analog device

A multimeter can measure continuity, resistance, voltage and sometimes even current, capacitance, temperature. The standard volt-ohm-millimeter (VOM) is an example of an analog measuring device. As the voltage, resistance, or current being measured by the VOM increases, the needle gradually and continuously moves up the scale. A digital multimeter (DMM) is an example of a digital measuring device. As the current, resistance, or voltage being measured by the DMM increases, the display jumps upward in small steps. The DMM is an example of digital circuitry taking over tasks previously performed only by analog devices. This turn toward digital circuitry is growing.