TDA5230 Datasheet, PDF (69/186 Pages) Infineon Technologies AG – Universal Low Power ASK/FSK Single Conversion Multi-Channel Image-Reject Receiver

TDA523x
2.4.8 Functionality of the IF Path
Functional Description
2.4.8.1 IF Filter
The output of the image reject mixer is buffered by the IF driver amplifier. The signal is
then filtered by one or (alternatively) two external 10.7 MHz IF filters.
IFBUF-IN
IFBUF-OUT LIM-IN+
LIM-IN-
IF-
Buffer-
Amp.
IF-
MUX
IF-LIMITER
RSSI-Generation
1
RSSI
A
D
To digital
FSK-Demodulator
and digital BB-
Processing
Figure 30 IF Path
For operation with one IF filter, this filter must be connected to the pins IF-OUT and LIM-
IN+.
For the two filter option, the first IF filter must be connected to the pins IF-OUT and
IFBUF-IN and the second filter to the pins IFBUF-OUT and LIM-IN+. The IF buffer
amplifier is enabled by the bit IFBUF to drive the second IF filter.
The IF MUX allows to bypass the second IF Filter, and therefore to switch in between
two different IF Filter bandwidths. The IF MUX is switched by using the bit IFMUX.
All input and output impedances seen by the IF filters (IF driver amplifier, IF buffer
amplifier and IF limiter input) are designed to 330 Ω.
Selection of the IF Filter
The construction of the TDA523x allows the use low-cost standard ceramic IF filters with
a center frequency of 10.7 MHz, and an input and output impedance of 330 Ω.
The recommended IF filter bandwidth is 280 kHz. See also (bill of material of the
evaluation board). Wider IF Filter bandwidth is required if transmitters with high tolerance
are used. Narrower IF Filter bandwidth will increase immunity to noise and improve
channel separation in multichannel systems.
Data Sheet
65
Version 4.0, 2007-06-01