Method for Electromagnetic Interference Reduction by using Die Paddle as Current Return/Shield
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
McMillan, TL: AUTHOR [+2]
A method for Electromagnetic Interference (EMI) reduction at a module level is disclosed. Specifically, for a module that has separated internal ground planes. The internal die paddle is used both as a shield and a current return path to reduce the radiated emissions.
Method for Electromagnetic Interference Reduction by
using Die Paddle
as Current Return/Shield
A method for
Electromagnetic Interference (EMI) reduction at a
module level is disclosed. Specifically, for a module that has
separated internal ground planes. The internal die paddle is used
both as a shield and a current return path to reduce the radiated
is useful for modules that make use of a Direct
Current (DC) isolated divided ground plane. Shielding and reduction
of current loop area is used.
A solution to
reducing the EMI radiated emissions can be
accomplished by using the die paddle both as a shield and a return
current path. Signals that communicate across isolated ground planes
can use the die paddle for their return current. Otherwise, the
return currents are forced to return outside the chip die and module
boundaries. These current loops create differential mode EMI
radiated emissions at the switching frequencies and associated
harmonics. These current loops can be effective radiators even if
the signals that generate them never leave the module.
The differential mode radiation in free space at a
distance of r is:
E = K(f*f*A*I)(1/r)sin0
K is a constant
f is the frequency in MHZ
A is the area of the loop in square meters
I is the current in Amperes
r is the distance in meters
sin0 is the angular orientation of the measuring antenna with
to the plane of the loop.
equation, it is obvious that for a given antenna
distance and orientation there are three methods to reduce the
emission. The frequency can be reduced, the current can be reduced,
or the loop area of the current path could be reduced. The method
disclosed reduces the loop area and consequently the emissions are
applications, for example a module that contains both
an analog section and a digital section, it can be functionally
attractive to maintain the individual DC ground sections. This
electrically isolates the two sections and helps to prevent the
digital switching noise from effecting the low level analog section.
Of course, the fewer signals that have to cross a DC ground boundary
the lower the emissions will be also.
With this basic configuration, the return curre...