PLL strategy trades jitter margin, lock time, and implementation complexity.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | robust | more overhead | new tapeout |
| Balanced | practical | needs rigor | mature flow |
| Aggressive | faster | high regressions | late stage |
| Architectural | durable | slow loop | recurring issue |
+------------------+----------------+----------------+----------------+Choose the smallest change that proves mechanism and preserves system margins.
Treating all AMS problems as analog-only
Skipping package and power evidence
AMS EVIDENCE MATRIX — Jitter Budgeting
+-------------------+------------------------+--------------------------+-------------------------+
| Evidence | Tells you | Does not prove | Next action |
+-------------------+------------------------+--------------------------+-------------------------+
| Waveform/log pair | sequence behavior | physical root cause | correlate with signoff |
| Signoff report | metric movement | contract correctness | audit assumptions |
| Floorplan view | physical proximity | dynamic mode behavior | run stress mode |
| Firmware trace | state progression | analog quality | combine with lab data |
| Dashboard summary | closure status | single-failure mechanism | inspect raw artifacts |
+-------------------+------------------------+--------------------------+-------------------------+Clock quality evidence must include jitter and sequencing, not lock status alone.
CLOCKING FLOW
reference -> PLL/DLL -> distribution -> endpoint marginJITTER TREND
jitter ps
^
| o baseline
| o stress mode
| o failure edgejitter budget
lock/unlock counters
phase-noise snapshot
STA uncertainty deltas
False-lock condition released reset early; endpoint logic sampled unstable clock edge patterns.
Lock qualification policy
Reset sequencing check
Package/supply contributors
Ask: what boundary condition proves this topic is actually closed?
State boundary, mode, and evidence tag with every claim.
Always align analog, digital, and physical owners before signoff decisions.
Fixing averages while tails still fail.
Skipping package/supply evidence in jitter or SerDes issues.
Shipping with waivers that lack owner and expiration criteria.
System timing margin is consumed by source jitter, transfer jitter, supply noise, and distribution skew; the budget must close from reference clock to endpoint sampler.
Metric: total jitter budget, deterministic/random split, downstream timing margin
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