T5744 Ver la hoja de datos (PDF) - Atmel Corporation

Número de pieza

componentes Descripción

Fabricante

T5744

UHF ASK/FSK Receiver

Atmel Corporation 

Receiving

Characteristics

The RF receiver T5744 can be operated with and without a SAW front-end filter. In a

typical automotive application, a SAW filter is used to achieve better selectivity. The

selectivity with and without a SAW front-end filter is illustrated in Figure 7. Note that the

mirror frequency is reduced by 40 dB. The plots are printed relatively to the maximum

sensitivity. If a SAW filter is used, an insertion loss of about 4 dB must be considered.

When designing the system in terms of receiving bandwidth, the LO deviation must be

considered as it also determines the IF center frequency. The total LO deviation is cal-

culated to be the sum of the deviation of the crystal and the XTO deviation of the T5744.

Low-cost crystals are specified to be within ±100 ppm. The XTO deviation of the T5744

is an additional deviation due to the XTO circuit. This deviation is specified to be

±30 ppm. If a crystal of ±100 ppm is used, the total deviation is ±130 ppm in that case.

Note that the receiving bandwidth and the IF-filter bandwidth are equivalent.

Figure 8. Receiving Frequency Response

0.0

-20.0

without SAW

-40.0

-60.0

-80.0

with SAW

-100.0

-6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0

df (MHz)

Basic Clock Cycle of the

Digital Circuitry

The complete timing of the digital circuitry and the analog filtering is derived from one

clock. According to Figure 9, this clock cycle TClk is derived from the crystal oscillator

(XTO) in combination with a divider. The division factor is controlled by the logical state

at Pin MODE. According to chapter 'RF Front End', the frequency of the crystal oscillator

(fXTO) is defined by the RF input signal (fRFin) which also defines the operating frequency

of the local oscillator (fLO).

Figure 9. Generation of the Basic Clock Cycle

TClk

Divider

:14/:10

f XTO

XTO

MODE

L : USA(:10)

16

H: Europe(:14)

DVCC

15

XTO

14

8 T5744

4521B–RKE–01/03

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