AX8052F151 datasheet(27/34 Pages) ONSEMI

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AX8052F151

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preamble, meaning that no interrupts will have to be

serviced by the microcontroller until a packet start is

detected.

The 802.15.4 is a universal DSSS mode, which can be

used with any modulation or data rate as long as it does not

violate the maximum data rate of the modulation being used.

Therefore the maximum DSSS data rate is 16 kbps for FSK

and 40 kbps for ASK and PSK.

RX AGC and RSSI

AX8052F151 features two receiver signal strength

indicators (RSSI):

1. RSSI before the digital IF channel filter.

The gain of the receiver is adjusted in order to

keep the analog IF filter output level inside the

working range of the ADC and demodulator. The

current value of the AGC and can be used as an

RSSI. The step size of this RSSI is 0.625 dB. The

value can be used as soon as the RF frequency

generation sub−system has been programmed.

2. RSSI behind the digital IF channel filter.

The demodulator also provides amplitude

information in the AX5051_TRK_AMPLITUDE

AX5051_AGCCOUNTER and the

AX5051_TRK_AMPLITUDE registers, a high

resolution (better than 0.1 dB) RSSI value can be

computed at the expense of a few arithmetic

operations on the microcontroller. Formulas for

this computation can be found in the AX5051

Programming Manual.

Modulator

Depending on the transmitter settings the modulator

generates various inputs for the PA:

Table 21.

Modulation

Bit = 0

Bit = 1

Main Lobe Bandwidth

Max. Bitrate

ASK

PA off

PA on

BW = BITRATE

600 kBit/s

FSK/MSK

Df = −fdeviation

Df = +fdeviation

BW = (1 + h) ⋅BITRATE

350 kBit/s

PSK

DF = 0°

DF = 180°

BW = BITRATE

600 kBit/s

= modulation index. It is the ratio of the

deviation compared to the bit−rate;

fdeviation = 0.5⋅h⋅BITRATE, AX8052F151 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

OQPSK = offset quadrature shift keying. The

AX8052F151 supports OQPSK. However,

unless compatibility to an existing system is

required, MSK should be preferred.

All modulation schemes are binary.

Automatic Frequency Control (AFC)

The AX8052F151 has a frequency tracking register

AX5051_TRKFREQ to synchronize the receiver frequency

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

can be computed with the following formula:

Df + TRKFREQ

216

BITRATE

FSKMUL

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.

PWRMODE Register

The AX8052F151 transceiver features its own

independent power management, independent from the

microcontroller. While the microcontroller power mode is

controlled

through

the

PCON

the

AX5051_PWRMODE register controls which parts of the

transceiver are operating.

Table 22. PWRMODE REGISTER

AX5051_PWRMODE

Name

Description

0000

POWERDOWN

All digital and analog transceiver functions, except the register file, are disabled. VREG is

reduced to conserve leakage power. The registers are still accessible.

0100

VREGON

All digital and analog transceiver functions, except the register file, are disabled. VREG,

however is at its nominal value for operation, and all registers are accessible.

0101

STANDBY

The crystal oscillator is powered on; receiver and transmitter are off.

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