AX5051 datasheet(29/44 Pages) ONSEMI

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Circuit Description

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AX5051

5.12. 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

600 kBit/s

FSK / MSK

f=-fdeviation

f=+fdeviation

BW=(1+h) BITRATE

350 kBit/s

PSK

=00

=1800

BW=BITRATE

600 kBit/s

Modulation index. It is the ratio of the deviation compared to the bit-rate.

AX5051 can demodulate signals with h < 32.

fdeviation

0.5hBITRATE

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

OQPSK

Offset quadrature shift keying.

The AX5051 supports OQPSK. However, unless compatibility to an existing system is

required, MSK should be preferred.

All modulation schemes are binary.

5.13. Automatic Frequency Control (AFC)

The AX5051 has a frequency tracking register

TRKFREQ to synchronize the receiver

frequency to a carrier signal. For AFC adjustment, the frequency offset can be computed

with the following formula:

FSKMUL

BITRATE

TRKFREQ







FSKMUL is the FSK oversampling factor, it depends on the FSK bit-rate and deviation

used. To determine it for a specific case, see the AX5051 Programming Manual. For

modulations other than FSK, FSKMUL=1.

AX5051 Datasheet(PDF) 29 Page - ON Semiconductor

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