W3000 Datasheet, PDF (12/28 Pages) Agere Systems – W3000 PLL Dual-Band Frequency Synthesizer

W3000 PLL Dual-Band Frequency Synthesizer
Advance Data Sheet
December 1999
REF Register (continued)
Table 10. D1: Forced Counter Reload (Bit 13)
D1
Response
0
Synchronous counter reloading update
1
Forced counter reload (M, R, A)
With synchronous reloading, the counter reloads a new programmed value when the counter reaches zero. With
forced counter reloading, the reloading occurs when the programmed word is latched in. This can improve lock
time when performing a dual-band hop.
Table 11. D2: Charge Pump Off Mode (Bit 14)
D2
Response
0
Charge pump enabled
1
Charge pump off (high impedance)
This allows the disabling of the charge pump for systems that directly modulate an open-loop VCO.
Table 12. Band and Charge Pump Current (Band 1, Bits 18 and 19; Band 2, Bits 15 and 16)
Band
1
1
1
1
2
2
2
2
D3
Bit 15
x
x
x
x
0
1
0
1
D4
Bit 16
x
x
x
x
0
0
1
1
D6
Bit 18
0
1
0
1
x
x
x
x
D7
Bit 19
0
0
1
1
x
x
x
x
Charge Pump Current
ISET
0.7 mA
0.9 mA
1.9 mA
2.5 mA
0.7 mA
0.9 mA
1.9 mA
2.5 mA
The charge pump current is selected by bit 23 of the MAIN register. Setting bit 23 to a 0 will select band 1, which
is established with bits 18 and 19 of the REF register. Likewise, setting bit 23 to a 1 will select band 2, which is
established with bits 15 and 16 of the REF register. This allows the charge pump current to be dynamically
changed along with the VCO frequency.
The PLL loop natural frequency is proportional to charge pump current and inversely proportional to the N count.
Therefore, when the ratio of charge pump current and VCO frequency is the same, the loop natural frequency
does not change. This allows the same loop filter to be used for two different VCO frequencies. For example, in a
GSM900/1800 system with VCOs running at 1190 MHz/1570 MHz, the current could be set to 1.9 mA for
GSM900 and 2.5 mA for GSM 1800 to compensate for the change in division ratios. The current setting may also
be determined by an external resistor. (See Table 15.) In that case, the ratio between the currents programmed
will stay the same, but the absolute level will be resistor-dependent.
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