Lecture №2 Pulse signals, basics of their description. Codes used in counting systems and digital devices

Lecture №2
Pulse signals, basics of their description. Codes used in counting systems and digital devices

.Description of pulse signals

Let's look at the basic terms. As an example, let us turn to an idealized impulse, which is called trapezoidal (Fig. 1, a). The pulse section AB is called the front, the section BC is called the top, the section SD is called the cut, the time segment AD - the basis. Sometimes the AB section is called the leading edge, and the CD section is called the trailing edge.
In Fig. 1, b shows other idealized pulses of characteristic shapes and gives their names.

Fig.1

Let us turn to an idealized, but more complex in shape pulse (Fig. 2,a).

The portion of the pulse corresponding to the negative voltage is called the tail of the pulse, or reverse surge.
For the quantities shown in the figure, the following names are usually used:
t _and – pulse duration;
t _f – duration of the pulse front;
t _s - pulse cutoff duration;
t _x - pulse tail duration;
U _m – amplitude (height) of the pulse;
∆U – decay of the top of the pulse;
U _arr – reverse ejection amplitude.



Fig.2

When determining the parameters of real pulses, it is usually not possible to unambiguously divide the pulse into characteristic sections; therefore, in these cases, the parameters of the pulses are determined based on certain agreements. For example, pulse and pulse rise times are often determined as shown in Fig. 2, b.

Let us turn to periodically repeating pulses (Fig. 3).



Fig.3
In this case, the following parameters are used:


T - pulse repetition period;
f = 1/T – pulse repetition frequency;
– pause duration;
Q = Т/t _and – duty cycle of pulses;
Кз = 1/Q = t _and /Т – _fill factor.

Types of microcircuit testing.

All tests are carried out in two directions: determining the limits of mechanical and climatic influences (the so-called determination of durability and design tests) and determining durability in various environmental conditions (periodic tests).

Evaluation tests are small samples tested under various mechanical and climatic conditions to determine operating limits.
Detected defects are classified by failure type (complete and gradual). We list the test conditions:

1. 
   mechanical shock load - ten consecutive impacts with acceleration up to 20,000 d within 1 ms;
   
2. 
   constant acceleration up to 100,000 d in different directions;
   
3. 
   storage of circuits for three days at temperatures above +25°C;
   
4. 
   storage of circuits for three days at a temperature of -60°C.
   

The main static characteristic of the circuits is the transfer characteristic:

- dependence of the potential at the output on the potential at one of the inputs at constant potential values ( or ) at the remaining inputs.
Based on the type of transfer characteristic, digital circuits are divided into inverting and non-inverting.

Control questions:

1) Basic definitions
2) Features of the IC
3) IC classification
4) Types of microcircuit tests