AN2321 Freescale Semiconductor / Motorola, AN2321 Datasheet - Page 14

• Manufacturer Part Number: AN2321
• Description: Designing for Board Level Electromagnetic Compatibility
• Manufacturer: Freescale Semiconductor / Motorola

AN2321/D
Series/Source
termination
Parallel termination
14
Series
Parallel
RC
Thevenin
Diode
Termination
Type
Relative
Medium
Medium
Cost
High
Low
Low
Figure 12
termination resistor, R
source, Z
load.
R
the real part in the equation: R
15 to 75 Ω .
Figure 13
resistor, R
not suitable for hand-held products, because of the low value of R
Designing for Board Level Electromagnetic Compatibility
S
must be placed as close as possible to the source driver. The value of R
Freescale Semiconductor, Inc.
Table 3. Summary of Termination Methods
For More Information On This Product,
Delay Added
Small
Small
Small
Small
S
P
, and the distributed trace, Z
Yes
shows the series/source termination method. The source
shows the parallel termination method. The parallel termination
, is added, such that R
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SOURCE
DRIVER
SOURCE
DRIVER
Figure 13. Parallel Termination Circuit
Figure 12. Series Termination Circuit
S
Required
, is added to achieve impedance matching between the
Medium
Power
Z
High
High
Low
Low
S
Z
S
R
S
S
= (Z
P
0
// Z
R
R = Z
R = Z
C = 20 to 600pF
R = 2 × Z
−Z
S
Z
Parameters
0
L
0
= Z
S
. It can also absorb reflection from the
) . Typically, R
Critical
is matched with Z
Z
0
0
0
0
—
= R
0
0
R
p
Z
L
S
Z
Good DC noise margin
Power consumption is a
Check bandwidth and
High power for CMOS
Limits overshoot; some
equals to approximately
L
problem
added capacitance
ringing at diodes
LOAD
0
C
Characteristics
. But this method is
d
LOAD
C
d
P
MOTOROLA
(typically
S
is