Page 135 - The Art and Science of Analog Circuit Design

Analog Breadboarding

Conclusion

It is not possible in a short chapter to discuss all the intricacies of suc-
cessful analog breadboard construction, but we have seen that the basic
principle is to remember all the laws of nature which apply and consider
their effects on the design.

Figure 9-23.

Pay attention to:
Resistance
Capacitance
Inductance
Decoupling
Ground
&
Separating sensitive circuits from noisy ones

In addition to the considerations of resistance, skin effect, capacitance,
inductance and ground current, it is important to configure systems so
that sensitive circuitry is separated from noise sources and so that the
noise coupling mechanisms we have described (common resistance/in-
ductance, stray capacitance, and mutual inductance) have minimal oppor-
tunity to degrade system performance. ("Noise" in this context means a
signal we want [or which somebody wants] in a place where we don't
want it; not natural noise like thermal, shot or popcorn noise.) The gen-
eral rule is to have a signal path which is roughly linear, so that outputs
are physically separated from inputs and logic and high level external
signals only appear where they are needed. Thoughtful layout is impor-
tant, but in many cases screening may be necessary as well.
A final consideration is the power supply. Switching power supplies
are ubiquitous because of their low cost, high efficiency and reliability,
and small size. But they can be a major source of HP noise, both broad-
band and at frequencies harmonically related to their switching
frequency. This noise can couple into sensitive circuitry by all the means
we have discussed, and extreme care is necessary to prevent switching
supplies from ruining system performance.
Prototypes and breadboards frequently use linear supplies or even
batteries, but if a breadboard is to be representative of its final version it
should be powered from the same type of supply. At some time during

118