AX5243_16 Datasheet, PDF (9/42 Pages) ON Semiconductor – Advanced High Performance ASK and FSK Narrow-band Transceiver

AX5243
Table 8. RF FREQUENCY GENERATION SUBSYSTEM (SYNTHESIZER)
Symbol
Description
Condition
Min Typ Max Units
f_REF
Reference frequency
The reference frequency must be chosen
10
16
50
MHz
so that the RF carrier frequency is not an
integer multiple of the reference frequency
Dividers
NDIV_ref Reference divider ratio range
Controlled directly with register REFDIV
2⁰
2³
NDIV_m
Main divider ratio range
Controlled indirectly with register FREQ
4.5
66.5
NDIV_RF RF divider range
Controlled directly with register RFDIV
1
2
Charge Pump
I_CP
Charge pump current
Programmable in increments of 8.5 mA via 8.5
register PLLCPI
2168
mA
Internal VCO (VCOSEL = 0)
f_RF
RF frequency range
RFDIV = 1
RFDIV = 0
400
525
MHz
800
1050
f_step
BW
T_start
RF frequency step
Synthesizer loop bandwidth
Synthesizer start−up time if crystal
oscillator and reference are running
RFDIV = 1, f_xtal = 16.000000 MHz
The synthesizer loop bandwidth and
start−up time can be programmed with
registers PLLLOOP and PLLCPI.
For recommendations see the AX5243
Programming Manual, the AX−RadioLab
software and AX5243 Application Notes
on compliance with regulatory regimes.
0.98
Hz
50
500
kHz
5
25
ms
PN868
Synthesizer phase noise 868 MHz
f_REF = 48 MHz
10 kHz offset from carrier
1 MHz offset from carrier
−95
−120
dBc/Hz
PN433
Synthesizer phase noise 433 MHz
f_REF = 48 MHz
10 kHz offset from carrier
1 MHz offset from carrier
−105
−120
dBc/Hz
VCO with external inductors (VCOSEL = 1, VCO2INT = 1)
f_{RFrng_lo}
f_{RFrng_hi}
RF frequency range
For choice of L_ext values as well as
VCO gains see Figure 3 and
Figure 4
RFDIV = 1
RFDIV = 0
27
262
MHz
54
525
PN169
Synthesizer phase noise 169 MHz
L_ext=47 nH (wire wound 0603)
RFDIV = 0, f_REF= 16 MHz
Note: phase noises can be
improved with higher f_REF
External VCO (VCOSEL = 1, VCO2INT = 0)
10 kHz from carrier
1 MHz from carrier
−97
−115
dBc/Hz
f_RF
V_amp
RF frequency range fully external
VCO
Note: The external VCO frequency needs
27
to be 2 x f_RF
1000 MHz
Differential input amplitude at L1, L2
terminals
0.7
V
V_inL
Input voltage levels at L1, L2
terminals
0
1.8
V
V_ctrl
Control voltage range
Available at FILT in external loop filter
0
mode
1.8
V
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