Electric Circuit

What are the differences between analog and digital?

The analog value can be directly recognized by people by sense. In contrast, the digital value basically changes its status to "1" or "0" and can be visually recognized by people when it is numerically converted.



Signals handled by an electric circuit are divided into analog signals and digital signals.
The analog signal is a voltage or current that continuously changes and the value of a voltage or current itself has its meaning.
The digital signal is defined a specific voltage or higher as a "high level" and a specific voltage or lower as a "low level". And used as non-continuous variable of "1" or "0". Take a bipolar transistor for example. The area where the collector-emitter voltage V_CE of the transistor linearly increases following upon the increasing of the collector current I_C while the base current I_B is held constant is the analog area (linear area). In contrast, the area where the collector-emitter voltage V_CE changes non-linearly is the digital area.



The analog IC is called the linear IC, because it is used in a linear area.

NEC Electronics classifies the product name codes by the process of each product.
uPB: Bipolar IC, digital
uPC: Bipolar IC, analog (linear)
uPD: MOS (digital) IC

What are the meanings of logic symbols?

The basic types of logic symbols are 1-input driver, multiple-input AND (logical product), and multiple-input OR (logical sum). Inverter (NOT), NAND (Not AND), and NOR (Not OR) that invert these symbols are also available. Inverted logic is called negative logic and is expressed by a logic circuit symbol with a small circle. In numeric expressions, logical inversion is indicated by an overscore on a signal name. If this overscore cannot be expressed because of text input or other reasons, "/", "!", or "#" is prefixed or suffixed to the signal name.
In addition, XOR (Exclusive OR) that is used for a comparator is also available as 2-input exclusive logical sum.
A driver (buffer), which does not change a logical value, is also used when the driving capability of a circuit in terms of voltage, current, or capacitance is insufficient.