ATA5425-PLSW datasheet(13/100 Pages) ATMEL

13 / 100 page

4841D–WIRE–10/07

ATA5423/ATA5425/ATA5428/ATA5429

Figure 3-2.

Measured Sensitivity 433.92 MHz/FSK/20 Kbit/s/±16 kHz/Manchester versus

Frequency Offset, Temperature and Supply Voltage

As can be seen in Figure 3-2 on page 13 the supply voltage has almost no influence. The tem-

perature has an influence of about +1.5/–0.7 dB, and a frequency offset of ±65 kHz also

influences by about ±1 dB. All these influences, combined with the sensitivity of a typical IC, are

then within a range of –103.7 dBm and –107.3 dBm over temperature, supply voltage and fre-

quency offset which is –105.5 dBm ±1.8dB. The integrated IF filter has an additional production

tolerance of only ±7 kHz, hence, a frequency offset between the receiver and the transmitter of

±58 kHz can be accepted for XTAL and XTO tolerances.

Note:

For the demodulator used in the ATA5423/ATA5425, the tolerable frequency offset does not

change with the data frequency, hence, the value of ±58 kHz is valid for up to 1

Kbit/s.

This small sensitivity spread over supply voltage, frequency offset and temperature is very

unusual in such a receiver. It is achieved by an internal, very fast and automatic frequency cor-

rection in the FSK demodulator after the IF filter, which leads to a higher system margin. This

frequency correction tracks the input frequency very quickly; if, however, the input frequency

makes a larger step (for example, if the system changes between different communication part-

ners), the receiver has to be restarted. This can be done by switching back to IDLE mode and

then again to RX mode. For that purpose, an automatic mode is also available. This automatic

mode switches to IDLE mode and back into RX mode every time a bit error occurs. (See “Digital

Control Logic” on page 36.)

-109

-108

-107

-106

-105

-104

-103

-102

-101

-100

-99

-98

-97

-96

-95

-110

-60

100

-40

-80

-100

Frequency Offset (kHz)

-20

VS = 3.0V Tamb = -40°C

VS = 3.6V Tamb = -40°C

VS = 3.0V Tamb = +25°C

VS = 3.6V Tamb = +25°C

VS = 2.4V Tamb = +105°C

VS = 3.0V Tamb = +105°C

VS = 3.6V Tamb = +105°C

VS = 2.4V Tamb = +25°C

VS = 2.4V Tamb = -40°C

ATA5425-PLSW Datasheet(PDF) 13 Page - ATMEL Corporation

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