ax5031 AXSEM, ax5031 Datasheet - Page 19

• Manufacturer Part Number: ax5031
• Description: Datasheet Ax5031
• Manufacturer: AXSEM

VCO
An on-chip VCO converts the control voltage generated by the charge pump and loop filter
into an output frequency. The frequency can be programmed in 1 Hz steps in the
FREQB
PLLLOOP
register must be programmed.
VCO Auto-Ranging
The
range for specific frequency generation subsystem settings automatically. Typically it has to
be executed after power-up. The function is initiated by setting the RNG_START bit in the
PLLRANGING
The RNGERR bit indicates the correct execution of the auto-ranging.
Loop Filter and Charge Pump
The
synthesizer loop band width. The loop-filter has three configurations that can be
programmed via the register bits FLT[1:0] in register PLLLOOP, the charge pump current can
be programmed using register bits PLLCPI[1:0] also in register PLLLOOP. Synthesizer
bandwidths are typically 50 - 500 kHz depending on the
section 4.3: AC Characteristics.
Registers
Register
PLLLOOP
FREQ
FREQB
PLLRANGING
Version 1.3
AX5031
AX5031
registers. To chose
must be set. For operation in the 433 MHz band, the BANDSEL bit in the
FREQSEL
FLT[1:0]
PLLCPI[2:0]
BANDSEL
has an integrated auto-ranging function, which allows to set the correct VCO
internal loop filter configuration together with the charge pump current sets the
register. The bit is readable and a 0 indicates the end of the ranging process.
Bits
Switches between carrier frequencies defined by FREQ and FREQB.
Using this feature allows to avoid glitches in the PLL output frequency caused by serially
changing the 4 bytes required to set a carrier frequency.
Synthesizer loop filter bandwidth, recommended usage is to increase the bandwidth
for faster settling time, bandwidth increases of factor 2 and 5 are possible.
Synthesizer charge pump current, recommended usage is to decrease the bandwidth
(and improve the phase-noise) for low data-rate transmissions.
Switches between 868 MHz/915 MHz and 433 MHz bands
Programming of the carrier frequency
Programming of the 2
FREQSEL=1.
Initiate VCO auto-ranging and check results
FREQB
setting rather than FREQ, the bit FREQSEL in register
nd
carrier frequency, switch to this carrier frequency by setting bit
Purpose
PLLLOOP
settings, for details see the
Circuit Description
Datasheet AX5031
PLLLOOP
FREQ
or
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