Page 164 - Troubleshooting Analog Circuits

Signal Sources 151

9.lV

f IN914 OR

-

-

b Va SETTLESOUICKLY TO
(W -15V .Rt +R,?

Figure 12.3. Either a clipping amplifier (a) or diode-limited bridge (b) will give you a clean, crisp square
wave.

whole megillah. I prefer to build up modular chunks, and to test each section as I get
it built. Then if it works, that provides a pleasant positive kick, several times along
the length of a project. But if it doesn’t work, it gives me a chance to get it on track
before I go charging ahead and get the whole thing finished. Sometimes it’s just a
missing capacitor. Other times, I’ve got the whole concept wrong, and the sooner
I find it out, the better. So if you see one of my systems made up of 14 little 7-inch
square sections, all lashed together on a master framework, don’t be surprised. I
mean, if vou can make a big system work the first time. more power to you. I
often remind my technician, “This may not work the first time, but it will be
reallv close. You may have to tweak an R here or a C there, but it won’t be disas-
trously bad.”
Similarly, when I have a circuit that does not work right40 I just want to get it
working right? Rather not. What I want is to learn what was wrong, and learn what
happens when I try changes. So I don’t give my technician a long list of changes to
make, all at once. I tell him, make this change first and see if the gain gets better. If
that doesn’t work, make that change and then that one, and keep an eye on the gain
and the phase. Then try this tweak on the output stage, and trim it for lower distortion
at 10 kHz.. . . If he made all the changes at once, the performance might improve. but
if we weren’t sure which changes made the improvement, we wouldn’t be learning
much, would we?

Systems and Circuits

When a system is designed, it is usually partitioned into subsections that are assigned
to different people or groups to engineer. Two very important ingredients in such a
system are Planning and Communication. If the partitioning was done unfairly, then
some parts of the system might be excessively easy to design, and other parts sub-
stantially impossible. We’ve all seen that happen, so we must be careful to prevent it
from happening to our systems. For if all the subsystems work except for one, the
whole project will probably fail.