CDCE62005 Datasheet, PDF (63/76 Pages) Texas Instruments – Five/Ten Output Clock Generator/Jitter Cleaner With Integrated Dual VCOs

CDCE62005
www.ti.com........................................................................................................................................................................................... SCAS862 – NOVEMBER 2008
Lock Detect
Digital Lock Detect
The CDCE62005 provides both an analog and a digital lock detect circuit. With respect to lock detect, two signals
whose phase difference is less than a prescribed amount are ‘locked’ otherwise they are ‘unlocked’. The phase
frequency detector / charge pump compares the clock provided by the input divider and the feedback divider;
using the input divider as the phase reference. The digital lock detect circuit implements a programmable lock
detect window. Table 43 shows an overview of how to configure the digital lock detect feature. When selecting
the digital PLL lock option, the PLL_LOCK pin will possibly jitter several times between lock and out of lock until
the PLL achieves a stable lock. If desired, choosing a wide loop bandwidth and a high number of successive
clock cycles virtually eliminates this characteristic. PLL_LOCK will return to out of lock, if just one cycle is outside
the lock detect window or if a cycle slip occurs.
Lock Detect Window (Max)
From Input Divider
From Feedback Divider
PFD /
CP
(a)
From Input Divider
Locked
From Feedback Divider
From Input Divider
Unlocked
From Feedback Divider
To Loop Filter
Lock Detect Window Adjust
Register 5
27 26 25 24 23 22
From Digital
Lock Detector
(b)
Figure 36. CDCE62005 Digital Lock Detect
PLL_LOCK
1 = Locked
O = Unlocked
(c)
Bit Name →
Register.Bit →
ADLOCK
5.27
1
X
X
0
0
0
0
0
•
0
0
Table 43. CDCE62005 Digital Lock Detect Control
DIGITAL LOCK DETECT
LOCKDET LOCKW(3) LOCKW(2)
5.26
5.25
5.24
X
X
X
0
X
X
1
X
X
X
0
0
X
0
0
X
0
0
X
0
1
X
0
1
•
•
•
X
1
1
X
X
X
LOCKW(1)
5.23
X
X
X
0
0
1
0
0
•
1
1
LOCKW(0)
5.22
X
X
X
0
1
0
0
1
•
0
1
Lock Detect Window
Analog Lock
1 cycle in lock window triggers a lock
64 continuous cycles in lock window triggers a
lock
Narrow Window
One step wider than narrow window
Two steps wider than narrow window
Three steps wider than narrow window
Four steps wider than narrow window
•
Widest Window
Reserved
Copyright © 2008, Texas Instruments Incorporated
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