You are required to design and simulate ( (A + B’)’ ) , logic gates using the “T

ID: 2082335 • Letter: Y

Question

You are required to design and simulate ( (A + B’)’ ) , logic gates using the “TTL (transistor-transistor logic) technology”. Below are some guidelines:

Try to make your design area efficient by using as less number of transistors as possible. Hint: Use De Morgan’s rule!

Use virtual DIP switches in your design to toggle the inputs.

Use a virtual LED/probe to demonstrate that the output is as expected.

You must be able to explain the working of your circuit in detail.

No implementation is required for this part.

Explanation / Answer

Ans-Introduction to TTLs:

It is a logic family consisting completely of transistors. It employs transistor with multiple emitters. Commercially it starts with the 74 series like the 7404, 74S86 etc. It was build in 1961 by James L Bui and commercially used in logic design in 1963

Classification of TTL:

TTLs are classified based on the output

Features of TTL Family:

Series of TTL IC:

TTL ICs mostly start with the 7 series. It has basically 6 subfamilies given as:

In any TTL device nomenclature, first two names indicate the name of the subfamily the device belongs to. The first two digits indicate the temperature range of operation. The next two alphabets indicate the subfamily the device belongs to. The last two digits indicate the logic function performed by the chip.

TTL Applications:

Typical TTL circuits

Logic Gates are used in daily life in applications like in clothes dryer, computer printer, door bell etc.

DeMorgan's Rules

As we look at boolean formulas, it's tempting to see something like:

(A + B)'

and try to apply some sort of distributive property to it with the NOT, resulting in something like:

A' + B'

However, if you break down these two statements into truth tables, you'll find they're not equivalent. So, we can't blindly distribute NOT's around.

DeMorgan looked at this problem, and developed a set of rules for dealing with this idea correctly. His rules state that when you're negating a logical expression, you must both:

Using DeMorgan's rules, we can see that:

(A + B)' = A' * B'

A logic probe is a low cost item of test equipment. As the name indicates, a logic probe tester is used for probing and analyzing logic circuits.

A logic probe tester is normally a small item of test equipment, typically handheld in the form of what could be thought of as a large oscilloscope probe, but without the lead.

This makes logic probes very portable and easy to use for troubleshooting and general simple maintenance work on low complexity logic circuitry.

For most applications, a logic probe would not be used within a laboratory test environment - here more sophisticated test equipment would be used because much closer investigation of problems is required.

Logic probe basics

A logic probe is able to give an indication of the logic state of a line carrying a digital signal The logic probe indicates whether there is a logic state "1" or "0", normally using an LED as the indicator. Often the LED on the logic probe will use different colours to indicate different states

A logic probe normally may be capable of indicating up to four different states:

Some logic probes may have a control to select the logic family being tested - different logic families have slightly different high and low voltage levels.

Another facility that some logic probes may include is an audible indication of the logic state. This feature is particularly useful when using a probe as eyes may need to be trained on the circuit and not on the logic probe itself.

Logic probe tester advantages and disadvantages

As with any item of test equipment, there are advantages and disadvantages to the use of a logic probe.

Logic probe advantages -

Logic probe disadvantages -

A logic probe tester is a cheap and relatively simple item of test equipment. It is versatile and very transportable, and it also is able to provide a quick test for many circuits. However it is not nearly as flexible as an oscilloscope or a logic analyzer. A logic probe can be used for quick testing, whereas for more in-depth testing more sophisticated test equipment is needed.