ML2721 Ver la hoja de datos (PDF) - Micro Linear Corporation
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ML2721 Datasheet PDF : 27 Pages
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PRELIMINARY
MODE OF OPERATION (CONTINUED)
ML2721
circuits do not reprogram the PLL for every receive or
transmit packet. The PLL divide register should be
programmed with a binary integer which represents the
desired RF channel frequency divided by 0.512 MHz
(when using a 6.144 or 12.288MHz reference frequency).
When in TRANSMIT mode the PLL is disabled and the
loop opened to allow modulation of the VCO. The VCO
runs at twice the channel frequency, and the Transmit RF
output is taken from one output of the quadrature divider.
The PLL locks during TXCAL mode.
The frequency plan for the PLL and VCO transmit is given
in Table 5.
When in RECEIVE mode the PLL is disabled to conserve
power and prevent PLL divider noise from desensitizing
the receiver. See Figure 8. The PLL frequency is set to
give a LO frequency equal to the desired RF channel
frequency plus the IF frequency. The VCO signal is
divided by two to provide the quadrature LO for the
image reject down convert mixer. The PLL locks during
RXCAL mode.
LOOP FILTER
PLLEN
VCO
(N+2) × FCOMP
DIVIDER
FCOMP
PD
÷2
N × FCOMP/2
INPUT SIGNAL AT
N × FCOMP/2
12
ADDER
N
2 REGISTER 1
BIT14...BIT3
IF AT FCOMP
FCOMP
÷6 or
÷12
REF
Figure 8. Phase Locked Loop in Receive Mode
Parameter
RF channel frequency register
Transmit RF output frequency
PLL division ratio
VCO frequency
PLL comparison frequency
Frequency resolution
Value Formula
N
N ´ (FCOMP/2)
N
N ´ FCOMP
FCOMP (~1MHz)
FCOMP/2
Definitions
1024 £ N £ 4093 for the complete divider range.
1762 £ N £ 1812 for the 902 to 928MHz ISM band.
Guaranteed to cover the range from 900 to 930MHz
The frequency division between the VCO and the phase
comparator
Range is 1.80 to 1.86GHz
Rate of charge pump pulses at charge pump output (QPO).
REF input frequency divided by 6 or 12.
At Transmit RF output
Table 5. Transmit Mode Frequency Relationsships
Parameter
RF channel frequency register
Channel frequency
LO frequency
IF frequency
PLL division ratio
VCO frequency
PLL comparison frequency
Frequency resolution
Value/Formula
Definitions
N
1024 £ N £ 4093 for the complete divider range
1762 £ N £ 1812 for the 902 to 928MHz ISM band
N ´ (FCOMP/2) Guaranteed to cover the range from 900 to 930MHz
(N + 2) ´
(FCOMP/2)
At the LO ports of the receiver mixer
~1.0MHz
Difference between LO frequency and channel frequency
N+2
The frequency division between the VCO and the phase
comparator
(N + 2) ´ FCOMP Range is 1.80 to 1.86GHz
FCOMP (~1.0MHz)
Rate of charge pump pulses at charge pump output (QPO)
FREF input frequency divided by 6 or 12
FCOMP/2
At Transmit RF output
Table 6. Receive Mode Frequency Relationships
14
PRELIMINARY DATASHEET January, 2000
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