LUCW3000CCN AGERE [Agere Systems], LUCW3000CCN Datasheet - Page 12

• Manufacturer Part Number: LUCW3000CCN
• Description: W3000 PLL Dual-Band Frequency Synthesizer
• Manufacturer: AGERE [Agere Systems]

W3000 PLL Dual-Band Frequency Synthesizer
REF Register
Table 10. D1: Forced Counter Reload (Bit 13)
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)
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)
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.
12
Band
D1
D2
0
1
0
1
1
1
1
1
2
2
2
2
Bit 15
Synchronous counter reloading update
D3
x
x
x
x
0
1
0
1
Charge pump off (high impedance)
(continued)
Forced counter reload (M, R, A)
Charge pump enabled
Bit 16
D4
x
x
x
x
0
0
1
1
Response
Response
Bit 18
D6
0
1
0
1
x
x
x
x
Bit 19
D7
0
0
1
1
x
x
x
x
Charge Pump Current
0.7 mA
0.9 mA
1.9 mA
2.5 mA
0.7 mA
0.9 mA
1.9 mA
2.5 mA
I
SET
Advance Data Sheet
Lucent Technologies Inc.
December 1999