Electrical engineer interview questions

1. What types of CMOS memories have you designed? What were their size? Speed? Configuration Process technology?
2. What work have you done on full chip Clock and Power distribution? What process technology and budgets were used?
3. What types of I/O have you designed? What were their size? Speed? Configuration? Voltage requirements? Process technology? What package was used and how did you model the package/system? What parasitic effects were considered?

4. What types of high speed CMOS circuits have you designed?
5. What transistor level design tools are you proficient with? What types of designs were they used on?
6. What products have you designed which have entered high volume production?
7. What was your role in the silicon evaluation/product ramp? What tools did you use?
8. If not into production, how far did you follow the design and why did not you see it into production?

Using Ideal Sources

The idea of using ideal sources is something that you may rebel at. After all, there is no such thing as an ideal source anywhere in the world. You can't pull an ideal source off the shelf in the lab, so why are we even talking about them? The answer to that question is that you use ideal sources when you have a non-ideal (a real source) source in a circuit. There are two important things to note.

* There are some sources that are very good sources and that can be modelled as ideal sources. (And when that happens, be grateful.) Some situations like that include the following.
o A power supply in the lab. Many times you connect a power supply to some electronic circuit, for example, and when you connect the circuit you find that the output voltage from the power supply doesn't change measurably. (After all, power supply designers try to make that happen!) In that case, the power supply might be considered to be an ideal source - at least as long as you are working on that particular circuit.
* There are many sources that do not perform ideally. However, it has proven to be possible to construct models of real sources, and those models often contain ideal source in combination with other ideal elements (like resistors, etc.). Thevinin and Norton equivalent circuits are examples of models of real sources that can account for loading effects (i.e. drawing enough current from the source to change the output voltage) and they are widely used in circuit analysis. You will even find that manufacturers give you parameter values for Thevinin and Norton equivalents on the front panel of many instruments like function generators.

You often have situations in which the sources that you use can be approximated with ideal sources. Shown below is a bridge circuit powered by a battery. Often a battery maintains a pretty constant voltage across the terminals, so you may be able to replace the battery with an ideal voltage source when you analyze the circuit.

Here's the circuit with an ideal voltage source substituted for the battery. At this point, you may know how to do the analysis so you're ready to go.

What Is An Ideal Current Source?

An ideal current source is a simple model for many current sources. It is reminiscent of the ideal voltage source - but with voltage and current interchanged. Here is the story.

* There is a special circuit symbol for an ideal current source. See below

* IL = constant, no matter what the terminal voltage is.
* The plot of load current against terminal voltage is similar to the plot for an ideal voltage source, but voltage and current are interchanged. Here is the plot.

Notice that an ideal current source is somewhat similar to an ideal voltage source. However, when you use an ideal source - usually when doing circuit analysis- there is a significant difference in the analysis. However, that's getting ahead of the story. We first have to worry about how you would "use" an ideal source, when we know that there is no such thing as an ideal source, i.e. a source that is "perfect" in some way.

Ideal Voltage Source?

The concept of an ideal voltage source is pretty simple,

* An ideal voltage source is a voltage source that maintains the same voltage across the source's terminals no matter what current is drawn from the terminals of the source or what current flows into the terminals.

That's it in a nutshell. If the source is a DC Source, we can plot a voltage current plot for an ideal voltage source. The plot is shown below. However, we need to define terms. Here is a circuit symbol for an ideal voltage source. In this symbol, we assume the following.

* The voltage across the terminals is denoted as Vt.
* The load current flowing from the source to a load (presumably a load is attached when the source is in a circuit) is denoted as IL.
* With those definitions, here is the source symbol. It's just a circle with polarity indicated.

And, here is the plot of terminal voltage against load current.

Given the discussion above, we can say:

* Vt = constant, no matter what the load current is.

That's pretty much the description of the ideal voltage source. It's not too complex, but it is an important concept. In the next section we'll look at how you can put this concept to use. For the rest of this section we'll look at ideal current sources starting next.

What Is An Electrical Source?

You probably suspect an electrical source has to be something that gives you a voltage or a current, and you would be correct. In fact, there are two different kinds of ideal electrical sources - voltage sources and current sources.