TDA5240 Datasheet, PDF (20/284 Pages) Infineon Technologies AG – Enhanced Sensitivity Multi-Channel Quad-Configuration Receiver

TDA5240
The bandpass filter follows the subsequent formula:
Functional Description
f_center = f_{corner, low} × f_{corner, high}
Therefore asymmetric corner frequencies can be observed. The use of AFC results in
more symmetry.
A multi-stage bandpass limiter at a center frequency of 274 kHz completes the receiver
chain. The -3dB corner frequencies of the bandpass limiter are typically at 75 kHz and
at 520 kHz.
An RSSI generator delivers a DC signal proportional to the applied input power and is
also used as an ASK demodulator. Via a programmable anti-aliasing filter this signal is
converted to the digital domain by means of a 10-bit ADC.
The limiter output signal is connected to a digital FSK demodulator.
The immunity against strong interference frequencies (so called blockers) is determined
by the available filter bandwidth, the filter order and the 3^rd order intercept point of the
front end stages. For Single-Channel applications with moderate requirements to the
selectivity the performance of the on-chip 3^rd order bandpass polyphase filter might be
sufficient. In this case no external filters are necessary and a single down conversion
architecture can be used, which converts the input signal frequency directly to the 2^nd IF
frequency of 274 kHz.
I-Mix
RX
Input
LNA
Q-Mix
1^st LO
IF
Attenuation
adjust
RX
I-
LP
digital ^{FSK Data}
Mix2
harm sup FSK Demod
RX
Q-
Mix2
RSSI Generator
LP
alias sup
ASK /
RSSI
ADC
ASK Data
Channel Filter
Bandwidth select
Divider
:N
2^nd LO
Figure 4 Single Down Conversion (SDC, no external filters required)
For Multi-Channel applications or systems which demand higher selectivity the double
down conversion scheme together with one or two external CER filters can be selected.
The order of such ceramic filters is in a range of 3, so the selectivity is further improved
and a better channel separation is guaranteed.
Data Sheet
20
V4.0, 2010-02-19