W3000 Datasheet, PDF (17/28 Pages) Agere Systems – W3000 PLL Dual-Band Frequency Synthesizer

Advance Data Sheet
December 1999
W3000 PLL Dual-Band Frequency Synthesizer
PLL Lock-Detect Function
The W3000 provides a basic lock-detect function for fault finding or for system specification requirements.
Inside the W3000, the length of the up or down pulses applied to the loop filter is compared with a reference
clock period. If the current pulses are shorter than a reference clock period for 15 consecutive comparison
periods, the LD line is asserted. If a current pulse is detected that is longer than a reference clock period, the LD
line is unset.
The LD line gives a signal to indicate a PLL fault condition. It does not provide a true loop-locked output. For
example, in a GSM system with a reference clock of 13 MHz and a comparison frequency of 200 kHz, the
current pulses only have to be less than 1/65 of a cycle for 15 consecutive times for the LD line to be asserted.
This equates to ~0.4º of phase. In the worst case, if the phase stays inside this limit, moving from one extreme to
the other, the frequency will only be within 0.2%, i.e., 4 MHz on a 2 GHz VCO.
The LD output from the W3000 is a standard logic signal and requires no external comparison or R-C filters.
Typical Performance Characteristics
CURRENT
METER _VDDC/2
UHF
SOURCE
+VDDC
100 pF
442 Ω 0.047 µF
6.8 pF
50 Ω
+VDD
100 pF
VDDC
LAT
CPOUT
DAT
VSS1
CLK
VSS2
MAIN_IN
VDD1
VDD2
PWRDN
REF_IN
0.01 µF
RREF = 18 k Ω
RES
50 Ω
LOCK DET
10 MHz REF
REFERENCE
SOURCE
µC
VDDC
Figure 8. MAIN_IN and REF_IN Sensitivity Test Circuit Diagram
MAIN_IN and REF_IN are set to cause a small beat frequency at the phase detector input. This generates a
sawtooth signal at the charge pump output of known slope. The amplitude of the UHF source is decreased. The
sensitivity limit is reached when the slope of this waveform deviates from the calculated value. This is then
repeated for the reference source.
Lucent Technologies Inc.
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