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TDA5251F1

ASK/FSK 315MHz Wireless Transceiver

Infineon Technologies 

TDA5251 F1

Version 1.1

Functional Description

2.4.7 I/Q Limiters

The I/Q Limiters are DC coupled multistage amplifiers with offset-compensating feedback circuit

and an overall gain of approximately 80dB each in the frequency range of 100Hz up to 350kHz.

Receive Signal Strength Indicator (RSSI) generators are included in both limiters which produce DC

voltages that are directly proportional to the input signal level in the respective channels. The

resulting I- and Q-channel RSSI-signals are summed to the nominal RSSI signal.

2.4.8 FSK Demodulator

The output differential signals of the I/Q limiters are fed to a quadrature correlator circuit that is used

to demodulate frequency shift keyed (FSK) signals. The demodulator gain is 2.4mV/kHz, the

maximum frequency deviation is ±300kHz as shown in Figure 2-4 below.

The demodulated signal is applied to the ASK/FSK mode switch which is connected to the input of

the data filter. The switch can be controlled by the ASKFSK pin (pin 4) and via the D11 bit in the

CONFIG register.

The modulation index m must be significantly larger than 2 and the deviation at least larger than

25kHz for correct demodulation of the signal.

1,6

1,5

1,4

1,3

1,2

1,1

1

0,9

0,8

0,7

0,6

0,5

-350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350

f /kHz

Figure 2-4 Quadricorrelator Demodulation Characteristic

Qaudricorrelator.wmf

Data Sheet

20

2007-02-26

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