ATA8201 datasheet(6/44 Pages) ATMEL

6 / 44 page

4971C–INDCO–04/09

ATA8201/ATA8202

RF Receiver

As seen in Figure 1-3 on page 5, the RF receiver consists of a low-noise amplifier (LNA), a local

oscillator, and the signal processing part with mixer, IF filter, IF amplifier with analog RSSI,

FSK/ASK demodulator, data filter, and data slicer.

In receive mode, the LNA pre-amplifies the received signal which is converted down to a

440-kHz intermediate frequency (IF), then filtered and amplified before it is fed into an FSK/ASK

demodulator, data filter, and data slicer. The received signal strength indicator (RSSI) signal is

available at the pin RSSI.

2.1

Low-IF Receiver

The receive path consists of a fully integrated low-IF receiver. It fulfills the sensitivity, blocking,

selectivity, supply voltage, and supply current specification needed to design, e.g., an industrial/

aftermarket integrated receiver for RKE and TPM systems. A benefit of the integrated receive fil-

ter is that no external components needed.

At 315 MHz, the ATA8201 receiver (433.92 MHz for the ATA8202 receiver) has a typical system

noise figure of 6.0 dB (7.0 dB), a system I1dBCP of –31 dBm (–30 dBm), and a system IIP3 of

–24 dBm (–23 dBm). The signal path is linear for out-of-band disturbers up to the I1dBCP and

hence there is no AGC or switching of the LNA needed, and a better blocking performance is

achieved. This receiver uses an IF (intermediate frequency) of 440 kHz, the typical image rejec-

tion is 30 dB and the typical 3-dB IF filter bandwidth is 420 kHz (f

IF = 440 kHz ± 210 kHz,

lo_IF = 230 kHz and fhi_IF = 650 kHz). The demodulator needs a signal-to-noise ratio of 8.5 dB for

10 Kbits/s Manchester with ±38 kHz frequency deviation in FSK mode, thus, the resulting sensi-

tivity at 315 MHz (433.92 MHz) is typically –105 dBm (–104 dBm).

Due to the low phase noise and spurs of the synthesizer together with the 8th-order integrated IF

filter, the receiver has a better selectivity and blocking performance than more complex double

superhet receivers, without using external components and without numerous spurious receiv-

ing frequencies.

A low-IF architecture is also less sensitive to second-order intermodulation (IIP2) than direct

conversion receivers where every pulse or amplitude modulated signal (especially the signals

from TDMA systems like GSM) demodulates to the receiving signal band at second-order

non-linearities.

ATA8201 Datasheet(PDF) 6 Page - ATMEL Corporation