tda5235 Infineon Technologies Corporation, tda5235 Datasheet - Page 20

• Manufacturer Part Number: tda5235
• Description: Enhanced Sensitivity Double-configuration Receiver With Digital Baseband Processing
• Manufacturer: Infineon Technologies Corporation

The bandpass filter follows the subsequent formula:
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
front end stages. For Single-Channel applications with moderate requirements to the
selectivity the performance of the on-chip 3
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
frequency of 274 kHz.
Figure 4
For Multi-Configuration applications requiring different RF channels 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
Input
RX
LNA
Q-Mix
1
I-Mix
st
LO
Single Down Conversion (SDC, no external filters required)
Attenuation
adjust
IF
f
center
=
f
corner low
20
,
rd
order bandpass polyphase filter might be
×
f
corner high
2
,
Mix2
Mix2
nd
Q-
I-
LO
rd
order intercept point of the
Bandwidth select
Channel Filter
Functional Description
RSSI Generator
V1.0, 2010-02-19
harm sup
alias sup
LP
LP
TDA5235
FSK Demod
ASK /
RSSI
ADC
Divider
digital
: N
nd
FSK Data
ASK Data
RX
RX
IF