Digital microcircuits. Types of logic, cases. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Well, first, let's say this: microcircuits are divided into two large types: analog and digital. Analog microcircuits work with an analog signal, and digital ones, respectively, with a digital one. We will talk specifically about digital microcircuits.

More precisely, we will not even talk about microcircuits, but about elements of digital technology that can be "hidden" inside the microcircuit.

What are these elements?

Some names you have heard, some you may not. But believe me, these names can be pronounced aloud in any cultural society - these are absolutely decent words. So, a rough list of what we will study:

• Triggers
• Counters
• Encoders
• Decoders
• Multiplexers
• Comparators
• RAM
• ROM

All digital circuits work with digital signals. What it is?

Digital Signals - these are signals that have two stable levels - the level of logical zero and the level of logical one. For microcircuits made using different technologies, the logical levels may differ from each other.

The two most widely used technologies are TTL and CMOS.

TTL - Transistor-Transistor Logic;

CMOS - Complementary Metal-Oxide-Semiconductor.

In TTL, the zero level is 0,4 V, the one level is 2,4 V.

With CMOS logic, the zero level is very close to zero volts, the one level is approximately equal to the supply voltage.

In any case, one - when the voltage is high, zero - when the voltage is low.

BUT! Zero voltage at the output of the microcircuit does not mean that the output is "hanging in the air." In fact, it is simply connected to a common wire. Therefore, you cannot directly connect several logical conclusions: if they have different levels, a short circuit will occur.

In addition to differences in signal levels, logic types also differ in terms of power consumption, speed (limiting frequency), load capacity, etc.

The type of logic can be recognized by the name of the chip. More precisely - by the first letters of the name, which indicate which series the microcircuit belongs to. Within any series there can be microcircuits produced using only one technology. To make it easier for you to navigate, here is a small summary table:

The most common today are the following series (and their imported counterparts):

• TTLSh - K555, K1533
• CMOS - KR561, KR1554, KR1564
• ESL - K1500

It is recommended to build digital circuits using microcircuits of only one type of logic. This is due precisely to differences in the logical levels of digital signals.

The type of logic is chosen mainly based on the following considerations:

- speed (working frequency)

- Energy consumption

- cost

But there are situations where one type is not enough. For example, one unit should be low power and the other high speed. CMOS technology chips have low consumption. ESL has high speed.

In this case, you will need to install level converters.

True, some types are normally joined without converters. For example, a signal from the output of a CMOS microcircuit can be applied to the input of a TTL microcircuit (assuming that their supply voltages are the same). However, it is not recommended to send a signal in the opposite direction, i.e., from TTL to CMOS.

Chips are available in various packages. The most common types of hulls are:

DIP

(Dual Inline Package)

The usual "cockroach". We put the legs into the holes on the board - and solder it.

The legs in the case can be 8, 14, 16, 20, 24, 28, 32, 40, 48 or 56.

The distance between the leads (pitch) is 2,5 mm (domestic standard) or 2,54 mm (bourgeois).

Lead width approx. 0,5 mm

The pin numbering is in the figure (top view). To determine the location of the first leg, you need to find the "key" on the body.

SEC

(Small Outline Integral Circuit)

Planar microcircuit - that is, the legs are soldered on the same side of the board where the case is located. At the same time, the microcircuit lies belly on the board.

The number of legs and their numbering are the same as for DIP.

The pin pitch is 1,25 mm (domestic) or 1,27 mm (bourgeois).

Pin width - 0,33...0,51

PLCC

(Plastic J-leaded Chip Carrier)

Square (rarely - rectangular) case. The legs are located on all four sides, and have a J-shape (the ends of the legs are bent under the abdomen).

Microcircuits are either soldered directly to the board (planar), or inserted into the socket. The latter is preferable.

Number of legs - 20, 28, 32, 44, 52, 68, 84.

Leg pitch - 1,27 mm

Pin width - 0,66...0,82

Pin numbering - the first leg near the key, increasing the number counterclockwise:

TQFP

(Thin Quad Flat Package)

Something between SOIC and PLCC.

The square case is about 1mm thick, the leads are located on all sides.

The number of legs is from 32 to 144.

Pitch - 0,8 mm

Output width - 0,3 ... 0,45 mm

Numbering - from the beveled corner (upper left) counterclockwise.

So, in general terms, the situation with the hulls. I hope now it will become a little easier for you to navigate in countless modern microcircuits, and you will not be driven into a stupor by the seller's phrase like: "this microcircuit is only available in a PLC case" ...