TDA5250D2 Datasheet, PDF (20/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

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TDA 5250 D2
preliminary
Functional Description
The bandwidth of the filters is controlled by the values set in the filter-register.
It can be adjusted between 50 and 350kHz in 50kHz steps via the bits D1 to D3
of the LPF register (subaddress 03H).
3.4.7 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.
3.4.8 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 3-4 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.
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 3-4 Quadricorrelator Demodulation Characteristic
Qaudricorrelator.wmf
Wireless Components
3 - 10
Specification, July 2002