mpc9893 Integrated Device Technology, mpc9893 Datasheet - Page 10

• Manufacturer Part Number: mpc9893
• Description: 3.3v 1 12 Lvcmos Pll Clock Generator
• Manufacturer: Integrated Device Technology

IDT™ / ICS™ 3.3V 1:12 LVCMOS PLL CLOCK GENERATOR
MPC9893
3.3V 1:12 LVCMOS PLL CLOCK GENERATOR
of an output driving a single line versus two lines. In both
cases the drive capability of the MPC9893 output buffer is
more than sufficient to drive 50 Ω transmission lines on the
incident edge. Note from the delay measurements in the
simulations a delta of only 43 ps exists between the two
differently loaded outputs. This suggests that the dual line
driving need not be used exclusively to maintain the tight
output-to-output skew of the MPC9893. The output waveform
in
by the impedance mismatch seen looking into the driver. The
parallel combination of the 36Ω series resistor plus the output
impedance does not match the parallel combination of the
line impedances. The voltage wave launched down the two
lines will equal:
unity reflection coefficient, to 2.6 V. It will then increment
towards the quiescent 3.0 V in steps separated by one round
trip delay (in this case 4.0 ns).
cause any false clock triggering, however designers may be
uncomfortable with unwanted reflections on the line. To better
match the impedances when driving multiple lines the
situation in
terminating resistors are reduced such that when the parallel
combination is added to the output buffer impedance the line
impedance is perfectly matched.
Figure 9
The waveform plots in
At the load end the voltage will double, due to the near
Since this step is well above the threshold region it will not
shows a step in the waveform, this step is caused
Figure 10
V
Z
R
R
V
0
L
S
0
L
= V
= 50 Ω || 50 Ω
= 36 Ω || 36 Ω
= 14 Ω
= 3.0 (25 ÷ (18+17+25)
= 1.31 V
Figure 11. CLK0, CLK1 MPC9893 AC Test Reference for V
S
should be used. In this case the series
(Z
Figure 9
0
÷ (R
Generator
Z = 50Ω
Pulse
S
+R
show the simulation results
0
+Z
0
))
Z
O
R
= 50Ω
T
= 50Ω
V
TT
MPC9893 DUT
10
3.0
2.5
2.0
1.5
1.0
0.5
0
Figure 10. Optimized Dual Line Termination
Figure 9. Single versus Dual Waveforms
MPC9893
Output
Buffer
14Ω
t
D
2
CC
14Ω + 22Ω || 22Ω = 50Ω || 50Ω
= 3.8956
OutA
In
= 3.3 V and V
Z
O
4
= 50Ω
25Ω = 25Ω
R
R
S
S
R
6
= 22Ω
= 22Ω
T
= 50Ω
Time (ns)
t
D
CC
= 3.9386
OutB
MPC9893 REV. 7 MARCH 3, 2008
8
= 2.5 V
V
TT
Z
Z
O
O
= 50Ω
= 50Ω
10
12
14