rf2059sr RF Micro Devices, rf2059sr Datasheet - Page 11

• Manufacturer Part Number: rf2059sr
• Description: High Performance Rf Pll/vco With Rf Mixers For Wlan Band Shifters
• Manufacturer: RF Micro Devices

Two PLL programming banks are provided, the first bank is preceded by the label PLL1 and the second bank is preceded by the
label PLL2. For the RF2059 these banks are used to program mixer 1 and mixer 2 respectively, and are selected automatically
as the mixer is selected (using the MODE pin).
The PLL will lock the VCO to the frequency F
where N
divider value (1 to 7).
The N divider is a fractional divider, containing a dual-modulus prescaler and a digitally spur-compensated fractional sequence
generator to allow fine frequency steps. The N divider is programmed using the N and NUM bits as follows:
First determine the desired, effective N divider value, N
N(9:0) should be set to the integer part of N
Example: VCO2 operating at 1800MHz, 23.92MHz reference frequency, the desired effective divider value is:
The N value is set to 75, equal to the integer part of N
by 2
Converting N and NUM into binary results in the following:
So the registers would be programmed:
The maximum N
for a 23.92MHz reference, the frequency step size would be 1.4Hz. The minimum reference frequency that could be used to
program a frequency of 2050MHz is 2050/511, 4.012MHz (approx).
Phase Detector and Charge Pump
The chip provides a current output to drive an external loop filter. An on-chip operational amplifier can be used to design an
active loop filter or a passive design can be implemented. The maximum charge pump output current is set by the value con-
tained in the P1_CP_DEF/P2_CP_DEF field and CP_LO_I.
In the default state (P1_CP_DEF/P2_CP_DEF=31 and CP_LO_I=0) the charge pump current (ICPset) is 120uA. If CP_LO_I is
set to 1 this current is reduced to 30uA.
The charge pump current can be altered by changing the value of P1_CP_DEF/P2_CP_DEF. The charge pump current is
defined as:
DS100630
24
:
EFF
is the programmed fractional N divider value, F
EFF
is 511, and the minimum N
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N
EFF
P1_NUM_MSB (or P2_NUM_MSB)=0100 0000 0011 0110
=F
VCO
NUM=0.25083612040 * 2
NUM=0100 0000 0011 0110 1100 1100
P1_NUM_LSB (or P2_NUM_LSB)=1100 1100
EFF
VCO
*R / F
. NUM should be set to the fractional part of N
EFF
according to:
P1_N (or P2_N)=0 0100 1011
OSC
ICP= ICPset*CP_DEF / 31
is 15, when in fractional mode. The minimum step size is F
F
N
=1800 *1 / 23.92=75.25083612040.
EFF
VCO
N=0 0100 1011
EFF
EFF
, and the NUM value is set to the fractional portion of N
=N
=F
:
OSC
VCO
EFF
*F
is the reference input frequency, and R is the programmed R
*R/F
OSC
24
OSC
/R
=4,208,332.
EFF
multiplied by 2
RF2059
OSC
24
/R*2
=16777216.
EFF
multiplied
24
11 of 38
. Thus