VCO, Stepsize
TX, Stepsize
PFD
x TX DIV
=
=
PLL DIV
PLL DIV
f
f
f
LO
TX
LO DIV x
TX DIV x
PLL DIV = Ceiling
= Ceiling
3000 MHz
3000 MHz
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39
SLWS245B – MAY 2014 – REVISED FEBRUARY 2017
Product Folder Links:
Copyright © 2014–2017, Texas Instruments Incorporated
8.4 Device Functional Modes
8.4.1 Selecting PLL Divider Values
With reference to the PLL architecture illustrated in
, operation of the PLL requires TX_DIV_SEL /
LO_DIV_SEL, PLL_DIV_SEL, RDIV, NINT, NFRAC and PRSC_SEL bits to be calculated.
a.
TX_DIV_SEL / LO_DIV_SEL
The LO to the integrated modulator (ƒ
TX
) and additional LO output (ƒ
LO
) frequency is related to f
VCO
according to the following:
ƒ
TX
= f
VCO
/ TX DIV
ƒ
LO
= f
VCO
/ LO DIV
Where TX DIV and LO DIV are related to TX_DIV_SEL and LO_DIV_SEL as:
TX_DIV_SEL / LO_DIV_SEL
TX_DIV / LO_DIV
FREQUENCY RANGE
TX_DIV_SEL = 0
TX DIV = 1
2050 MHz
≤
ƒ
TX
≤
4100 MHz
TX_DIV_SEL = 1
TX DIV = 2
1025 MHz
≤
ƒ
TX
≤
2050 MHz
TX_DIV_SEL = 2
TX DIV = 4
512.5 MHz
≤
ƒ
TX
≤
1025 MHz
TX_DIV_SEL = 3
TX DIV = 8
256.25 MHz
≤
ƒ
TX
≤
512.5 MHz
LO_DIV_SEL = 0
LO DIV = 1
2050 MHz
≤
ƒ
LO
≤
4100 MHz
LO_DIV_SEL = 1
LO DIV = 2
1025 MHz
≤
ƒ
LO
≤
2050 MHz
LO_DIV_SEL = 2
LO DIV = 4
512.5 MHz
≤
ƒ
LO
≤
1025 MHz
LO_DIV_SEL = 3
LO DIV = 8
256.25 MHz
≤
ƒ
LO
≤
512.5 MHz
b.
PLL_DIV_SEL
Given f
VCO
, select PLL_DIV_SEL so that the division ratio PLL DIV limits the input frequency to the
prescaler , f
DMP
, is limited to a maximum of 3000 MHz.
PLL DIV = min(1, 2, 4) such that f
DMP
≤
3000 MHz
PLL DIV is related to PLL_DIV_SEL according to the following equation:
PLL_DIV = 2
PLL_DIV_SEL
This calculation can be restated as
.
(6)
For both integer and fractional mode it is preferable to operate the f
PFD
at the highest possible frequency
determined by the required frequency step of the RFOUT or LO_OUT. In Integer mode, select the maximum
f
PFD
according to
(7)
In Fractional mode, small RF stepsize can be obtained through the fractional divider. In this case, the highest
f
PFD
frequency should be selected according to the reference clock and system requirements.