HMC7043 Datasheet, PDF (23/44 Pages) Analog Devices – JEDEC JESD204B support

HMC7043
Clock Grouping, Skew, and Crosstalk
Although the output channels are logically independent, for
physical reasons, they are first grouped into pairs, called clock
groups. Each clock group shares a reference, an input buffer,
and a SYNC retime flip flop originating from the clock
distribution network.
The second level of grouping is according to the supply pin. Clock
Group 1 (Channel 2 and Channel 3) is on an independent supply,
and the other supply pins are each responsible for two clock groups.
As the output channels are more tightly coupled (by sharing a
clock group or by sharing a supply pin), the skew is minimized.
However, the isolation between those channels suffers.
Table 15 shows the clock grouping by location, and Table 16
show the typical skew and isolation that can be expected and how
it scales with distance between output channels.
Isolation improves as either the aggressor or the affected
frequencies decrease. Nevertheless, for particularly important
clock channels where spurious tones must be minimized, carefully
consider their frequency and channel configurations to isolate
continuously running frequencies onto different supply domains.
Channels configured as pulse generators are normally not an
issue, because they are disabled during normal operation.
Data Sheet
Table 15. Supply Pin Clock Grouping by Location
Supply Pin Location
Clock Group Channel
VCC2_OUT
Southwest
1
2
3
VCC3_OUT
South
2
4
5
3
6
7
VCC6_OUT
Northeast
4
8
9
5
10
11
VCC7_OUT
Northwest
6
12
13
0
0
1
Table 16. Typical Skew and Isolation vs. Distance
Distance
Typical
1 GHz Isolation,
Skew (ps) Differential (dB)
Distant Supply Group
±20
90 to 100
Closest Neighbor on
±15
70
Different Supply Group
Shared Supply
±10
60
Same Clock Group
±10
45
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