T5744 Просмотр технического описания (PDF) - Atmel Corporation

Номер в каталоге

Компоненты Описание

производитель

T5744

UHF ASK/FSK Receiver

Atmel Corporation 

Figure 6. Input Matching Network without SAW Filter

fRF = 433.92 MHz

C3

25n

15p

8 LNAGND

T5744

9

LNA_IN

RFIN

3.3p

22n

100p

TOKO LL2012

F22NJ

fRF = 315 MHz

C3

25n

33p

8 LNAGND

T5744

9

LNA_IN

RFIN

3.3p

39n

100p

TOKO LL2012

F39NJ

Please note that for all coupling conditions (see Figure 5 and Figure 6), the bond wire

inductivity of the LNA ground is compensated. C3 forms a series resonance circuit

together with the bond wire. L = 25 nH is a feed inductor to establish a DC path. Its value

is not critical but must be large enough not to detune the series resonance circuit. For

cost reduction, this inductor can be easily printed on the PCB. This configuration

improves the sensitivity of the receiver by about 1 dB to 2 dB.

Analog Signal Processing

IF Amplifier

RSSI Amplifier

Pin RSSI

The signals coming from the RF front end are filtered by the fully integrated 4th-order IF

filter. The IF center frequency is fIF = 1 MHz for applications where fRF = 315 MHz or

fRF = 433.92 MHz is used. For other RF input frequencies, refer to Table 1 to determine

the center frequency.

The receiver T5744 employs an IF bandwidth of BIF = 600 kHz and can be used

together with the U2741B in ASK mode.

The subsequent RSSI amplifier enhances the output signal of the IF amplifier before it is

fed into the demodulator. The dynamic range of this amplifier is DRRSSI = 60 dB. If the

RSSI amplifier is operated within its linear range, the best S/N ratio is maintained. If the

dynamic range is exceeded by the transmitter signal, the S/N ratio is defined by the ratio

of the maximum RSSI output voltage and the RSSI output voltage due to a disturber.

The dynamic range of the RSSI amplifier is exceeded if the RF input signal is about

60 dB higher compared to the RF input signal at full sensitivity.

The output voltage of the RSSI amplifier (VRSSI) is available at Pin RSSI. Using the

RSSI output signal, the signal strength of different transmitters can be distinguished.

The usable input power range PRef is -100 dBm to -55 dBm.

Since different RF input networks may exhibit slightly different values for the LNA gain,

the sensitivity values given in the electrical characteristics refer to a specific input

matching. This matching is illustrated in Figure 6 and exhibits the best possible

sensitivity.

6 T5744

4521B–RKE–01/03

Share Link: