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

Número de pieza

componentes Descripción

Fabricante

T5744

UHF ASK/FSK Receiver

Atmel Corporation 

T5744

ASK Demodulator and

Data Filter

Figure 7. RSSI Characteristics

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

-130.0

Tamb = 40°C

25°C

105°C

max.

min.

-110.0

-90.0

-70.0

PRef (dBm)

-50.0

-30.0

The signal coming from the RSSI amplifier is converted into the raw data signal by the

ASK demodulator.

An automatic threshold control circuit (ATC) is employed to set the detection reference

voltage to a value where a good signal-to-noise ratio is achieved. This circuit also

implies the effective suppression of any kind of inband noise signals or competing trans-

mitters. If the S/N ratio exceeds 10 dB, the data signal can be detected properly.

The output signal of the demodulator is filtered by the data filter before it is fed into the

digital signal processing circuit. The data filter improves the S/N ratio as its passband

can be adopted to the characteristics of the data signal. The data filter consists of a 1st-

order highpass and a 1st-order lowpass filter.

The highpass filter cut-off frequency is defined by an external capacitor connected to Pin

CDEM. The cut-off frequency of the highpass filter is defined by the following formula:

fcu_DF = ------------------------1-------------------------

2 ´ p ´ R1 ´ CDEM

Recommended values for CDEM are given in the electrical characteristics.

The cut-off frequency of the lowpass filter is defined by the selected baudrate range

(BR_Range). BR_Range is defined by the Pins BR_0 and BR_1. BR_Range must be

set in accordance to the used baudrate.

BR_1

0

0

1

1

BR_0

0

1

0

1

BR_Range

0

1

2

2

Each BR_Range is defined by a minimum and a maximum edge-to-edge time (tee_sig).

These limits are defined in the electrical characteristics. They should not be exceeded to

maintain full sensitivity of the receiver.

7

4521B–RKE–01/03

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