This DFE rule checks for the connectivity of capacitors or diodes that have
polarities.
Polarized components, such as electrolytic capacitors and diodes, have a
characteristic of one directional current flow.
The unidirectional behavior provides a variety of useful functions in electronics
design. For example, power supply filtering, AC/DC filtering and extracting
modulation from radio signals.
However, reversing the current flow may result in damaging the component or cause a
circuit malfunction. This rule checks for the placement of components that have
polarities.
Item: Enter the item name.
Net: Select a target net group.
Component: Select a target component group that should be connected to the
net group.
Pin Name: Define names of connected pins. Multiple pin names can be entered
by a string format.
Compare Connection: This rule compares trace connectivity to the net
list. Figure 1.
Signal pattern SW-1 has a connection to the pin 1 of component D1.
If the component is placed reversely, the circuit cannot operate. Many
cases of diode, capacitor or TR components have connected pin
polarities. Check the circuit’s polarity to reduce mistakes.
Polarized Capacitor
Some capacitors are manufactured so they can only tolerate applied voltage in one
polarity but not the other. This is due to their construction. The dielectric is a
microscopically thin layer of insulation deposited on one of the plates by a DC
voltage during manufacture. These are called electrolytic (polarized) capacitors,
and their polarity is clearly marked. Figure 2.
Reversing voltage polarity to an electrolytic capacitor may result in the destruction
of that super-thin dielectric layer, thus ruining the device. However, the thinness
of that dielectric permits extremely high values of capacitance in a relatively
small package size. For the same reason, electrolytic capacitors tend to be low in
voltage rating as compared with other types of capacitor construction. Figure 3.
Diode Polarity
A diode is a two-terminal component that conducts current in only one direction. It
is a crystalline piece of semiconductor material connected to two electrical
terminals. The most common function of a diode is to allow an electric current to
pass in one direction (forward direction) while blocking current in the opposite
direction (the reverse direction). Thus, the diode can be thought of as an
electronic version of a check valve. This unidirectional behavior is called
rectification and is used to convert alternating current to direct current.
Diodes can have more complicated behavior than thesimple on-off action. This is due
to their complex non-linear electrical characteristics, which can be tailored by
varying the construction of their P-N junction. These are exploited in special
purpose diodes that perform many different functions.
The I-V characteristic of an ideal diode in either forward or reverse bias (no bias)
is:
Where,
Diode current.
Reverse bias saturation current.
Voltage across the diode.
Ideality factor, quality factor, or emission factor.
