AXM0F243 datasheet(33/53 Pages) ONSEMI

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AXM0F243

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TRANSCEIVER

The transceiver block is controllable through its registers.

The transceiver block features its own 256 byte FIFO. The

microcontroller can be interrupted at a programmable FIFO

fill level.

RF Frequency Generation Subsystem

The RF frequency generation subsystem consists of a

fully integrated synthesizer, which multiplies the reference

frequency from the crystal oscillator to get the desired RF

frequency. The advanced architecture of the synthesizer

enables frequency resolutions of 1 Hz, as well as fast settling

times of 5 – 50

ms depending on the settings (see section AC

Characteristics). Fast settling times mean fast start−up and

fast RX/TX switching, which enables low−power system

design.

For receive operation the RF frequency is fed to the mixer,

for transmit operation to the power−amplifier.

The frequency must be programmed to the desired carrier

frequency.

The synthesizer loop bandwidth can be programmed, this

serves three purposes:

1. Start−up time optimization, start−up is faster for

higher synthesizer loop bandwidths

2. TX spectrum optimization, phase−noise at

300 kHz to 1 MHz distance from the carrier

improves with lower synthesizer loop bandwidths

3. Adaptation of the bandwidth to the data−rate. For

transmission of FSK and MSK it is required that

the synthesizer bandwidth must be in the order of

the data−rate.

VCO

An on−chip VCO converts the control voltage generated

by the charge pump and loop filter into an output frequency.

This frequency is used for transmit as well as for receive

operation. The frequency can be programmed in 1 Hz steps

in the AX5043_FREQ registers. For operation in the 433

MHz band, the RFDIV bit in the AX5043_PLLVCODIV

The fully integrated VCO allows to operate the device in

the frequency ranges 800 – 1050 MHz and 400 – 520 MHz.

The carrier frequency range can be extended to 54 –

525 MHz and 27 – 262 MHz by using an appropriate

external inductor between device pins L1 and L2. The bits

VCO2INT and VCOSEL in the AX5043_PLLVCODIV

It is also possible to use a fully external VCO by setting

bits

VCO2INT = 0

and

VCOSEL = 1

the

AX5043_PLLVCODIV register. A differential input at a

frequency of double the desired RF frequency must be input

at device pins L1 and L2. The control voltage for the VCO

can be output at device pin FILT when using external filter

mode. The voltage range of this output pin is 0 – 1.8 V. This

mode of operation is recommended for special applications

where the phase noise requirements are not met when using

the fully internal VCO or the internal VCO with external

inductor.

VCO Auto−Ranging

The AXM0F243 has an integrated auto−ranging function,

which allows to set the correct VCO 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

AX5043_PLLRANGINGA or AX5043_PLLRANGINGB

ranging

process.

Setting

RNG_START

the

AX5043_PLLRANGINGA register ranges the frequency in

AX5043_FREQA, while setting RNG_START in the

AX5043_PLLRANGINGB register ranges the frequency in

AX5043_FREQB. The RNGERR bit indicates the correct

execution of the auto−ranging. VCO auto−ranging works

with the fully integrated VCO and with the internal VCO

with external inductor.

Loop Filter and Charge Pump

The AXM0F243 internal loop filter configuration

together with the charge pump current sets the synthesizer

loop band width. The internal loop−filter has three

configurations that can be programmed via the register bits

FLT[1:0]

registers

AX5043_PLLLOOP

AX5043_PLLLOOPBOOST the charge pump current can

be programmed using register bits PLLCPI[7:0] in registers

AX5043_PLLCPI

AX5043_PLLCPIBOOST.

Synthesizer bandwidths are typically 50 – 500 kHz

depending

the

AX5043_PLLLOOP

AX5043_PLLLOOPBOOST settings, for details see the

section: AC Characteristics.

The AXM0F243 can be setup in such a way that when the

synthesizer is started, the settings in the registers

AX5043_PLLLOOPBOOST

and

AX5043_PLLCPIBOOST are applied first for a

programmable duration before reverting to the settings in

AX5043_PLLLOOP and AX5043_PLLCPI

. This feature

enables automated fastest start−up.

Setting bits FLT[1:0] = 00 bypasses the internal loop filter

and the VCO control voltage is output to an external loop

filter at pin FILT. This mode of operation is recommended

for achieving lower bandwidths than with the internal loop

filter and for usage with a fully external VCO.

AXM0F243 Datasheet(PDF) 33 Page - ON Semiconductor

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