COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 174

• Manufacturer Part Number: COP8SA-DM
• Description: MODULE DEBUGGING FOR COP8SA
• Manufacturer: National Semiconductor

Specifications of COP8SA-DM

• Module/board Type: Debugger Module
• For Use With/related Products: Cop 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *COP8SA-DM

2.23.1 Introduction
CMOS has become the technology of choice for the processors used in many embedded
systems due to its capability for low standby power consumption. However, CMOS is
prone to high current transients on the power supply as the internal logic switches. These
transients can easily be the source of high-frequency emissions from the system. The
system designer should anticipate and minimize unwanted electromagnetic interference
(EMI).
2.23.2 Emission Predictions
“EMI in a typical electronic circuit is generated by a current flowing in a loop configured
within the circuit. These paths can be either V
EMI generation is a function of several factors. Transmitted signal frequency, duty cycle,
edge rates, and output voltage swings are the major factors of the resultant EMI levels.”
The formula for predicting the Electric Field emissions from such a loop is as follows:
where:
Applying this equation to a single standard output for a National Semiconductor
Microcontroller, and performing a Fourier analysis of the output switching at a frequency
of 20 MHz, yields the results shown in Table 2-12. These calculations assume a trace
length of 5 inches, a board thickness of 0.062 inches and a full ground plane. The load
capacitance is 100 pf.
Note that the assumption is made that the output is switching at 20 MHz, which is rarely
the case for a port output. There is noise, however, on the output at these frequencies due
to switching within the device. This is the noise which is coupled to the output through
V
2-136
CC
• |E|
• I is the current amplitude in milliamps
• A is the loop area in square cm
•
• D is the observation distance in meters
• Freq is the frequency in MHz
• and the perimeter of the loop P << .
1. “FACT
and GND. Another point to keep in mind is that rarely does one single output switch,
COP8SAx7 MICROCONTROLLER
is the wavelength at the frequency of interest in meters
MAX
Advanced CMOS Logic Databook”, National Semiconductor, 1993
is the maximum E-field in the plane of the loop in V/m
E
MAX
=
1.32 10
-------------------------------------------------------- -
3 –
D
IA Freq
CC
-to-GND loops or output-to-GND loops.
2
1
+
-----------
2 D
2
1 2 /
1