TDA5255E1_07 Datasheet, PDF (20/91 Pages) Infineon Technologies AG – ASK/FSK 434MHz Wireless Transceiver

TDA5255 E1
Version 1.2
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