AD14160KB-4 AD [Analog Devices], AD14160KB-4 Datasheet - Page 41

• Manufacturer Part Number: AD14160KB-4
• Description: Quad-SHARC DSP Multiprocessor Family
• Manufacturer: AD [Analog Devices]

GROUND BOUNCE ESTIMATE
Ground bounce diminishes noise margins in a system and must
be held as low as possible. Ground bounce results from switch-
ing output pins from a high to a low state with the ensuing dis-
charge current creating a voltage across the parasitic inductance
of the MCM’s ground pins (and to a lesser extent across the
wirebond wires connecting the ground pads). A useful model for
calculating the level of ground bounce is shown below (Johnson,
Howard W. and Graham, Martin, “High-Speed Digital Design,”
Prentice Hall p67, 1993).
REV. A
V
GND
V
IN
INDUCTANCE
GROUND PIN
L
GND
SYSTEM GROUND PLANE
Figure 40.
V
DD
I
DISCHARGE
SHARC DIE
LOAD C
–41–
In the Quad-SHARC module, the worse case ground bounce
condition occurs during an external memory operation in which
86 signals switch simultaneously from high to low. Because of
the ground planes embedded within the substrate of the mod-
ule, the effective ground pin inductance is found by dividing the
CBGA’s single ground pin inductance, estimated to be about
3 nH, by the 64 ground pins resulting in L
Typical output fall times for varying load conditions can be
obtained from this data sheet.
The induced voltage generated by the switching currents is
given by
Assuming the voltage waveform is an integrated Gaussian pulse,
the peak amplitude is approximated by
Calculated ground bounce maximum values for the CBGA
module are listed below.
Load per Output
(pF)
20
100
200
|V
V
GND
GND
| max = L
= L
Fall Time
(ns)
1.8
4.2
7.4
GND
AD14160/AD14160L
dt
d
GND
(I
DISCHARGE
1.52 V
T
10–90
GND
2
Ground Bounce
(V)
0.161
0.148
0.095
)
C.
= 0.05 nH.