AX5243 datasheet(36/65 Pages) ONSEMI

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Circuit Description

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AX5243

5.13. Modulator

Depending on the transmitter settings the modulator generates various inputs for the

PA:

Modulation

Bit = 0

Bit = 1

Main Lobe

Bandwidth

Max. Bitrate

ASK

PA off

PA on

BW=BITRATE

125 kBit/s

FSK/MSK/GFSK/GMSK f=-fdeviation

f=+fdeviation

BW=(1+h) BITRATE

125 kBit/s

PSK

=00

=1800

BW=BITRATE

125 kBit/s

= modulation index. It is the ratio of the deviation compared to the bit-

rate; fdeviation = 0.5hBITRATE, AX5243 can demodulate signals with h < 32.

ASK

= amplitude shift keying

FSK

= frequency shift keying

MSK

= minimum shift keying; MSK is a special case of FSK, where h = 0.5, and

therefore fdeviation = 0.25BITRATE; the advantage of MSK over FSK is that it can be

demodulated more robustly.

PSK

= phase shift keying

All modulation schemes, except 4-FSK, are binary.

Amplitude can be shaped using a raised cosine waveform. Amplitude shaping will also be

performed for constant amplitude modulation ((G)FSK, (G)MSK) for ramping up and

down the PA. Amplitude shaping should always be enabled.

Frequency shaping can either be hard (FSK, MSK), or Gaussian (GMSK, GFSK), with

selectable BT=0.3 or BT=0.5.

Modulation

DiBit = 00

DiBit = 01

DiBit = 11

DiBit = 10

Main Lobe

Bandwidth

Max. Bitrate

4-FSK

f=-3fdeviation

f=-fdeviation

f=+fdeviation f=+3fdeviation

BW=(1+3h)

BITRATE

115.2 kBit/s

4-FSK Frequency shaping is always hard.

5.14. Automatic Frequency Control (AFC)

The AX5243 features an automatic frequency tracking loop which is capable of tracking

the transmitter frequency within the RX filter band width. On top of that the AX5243

has a frequency tracking register

TRKRFFREQ to synchronize the receiver frequency to a

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