TDA5212_06 Datasheet, PDF (20/49 Pages) Infineon Technologies AG – ASK/FSK 915MHz Single Conversion Receiver

TDA 5212
Functional Description
pin (Pin 15) as shown in the following table. This gain was chosen to facilitate
detection in the subsequent circuits.
Table 3-3 MSEL Pin Operating States
MSEL
Open
Shorted to ground
Modulation Format
ASK
FSK
The DC gain is 1 in order not to saturate the subsequent Data Filter wih the DC
offset produced by the demodulator in case of large frequency offsets of the IF
signal. The resulting frequency characteristic and details on the principle of
operation of the switch are described in Section 4.6. The demodulator circuit is
switched off in case of reception of ASK signals.
3.4.7 Data Filter
The data filter comprises an OP-Amp with a bandwidth of 100kHz used as a
voltage follower and two 100kΩ on-chip resistors. Along with two external
capacitors a 2nd order Sallen-Key low pass filter is formed. The selection of the
capacitor values is described in Section 4.2.
3.4.8 Data Slicer
The data slicer is a fast comparator with a bandwidth of 100 kHz. This allows
for a maximum receive data rate of approximately 120kBaud. The maximum
achievable data rate also depends on the IF Filter bandwidth and the local oscil-
lator tolerance values. Both inputs are accessible. The output delivers a digital
data signal (CMOS-like levels) for the detector. The self-adjusting threshold on
pin 20 its generated by RC-term or peak detector depending on the baseband
coding scheme. The data slicer threshold generation alternatives are described
in more detail in Section 4.5.
3.4.9 Peak Detector
The peak detector generates a DC voltage which is proportional to the peak
value of the receive data signal. An external RC network is necessary. The input
is connected to the output of the RSSI-output of the Limiter, the output is con-
nected to the PDO pin (Pin 26 ). This output can be used as an indicator for the
received signal strength to use in wake-up circuits and as a reference for the
data slicer in ASK mode. Note that the RSSI level is also output in case of FSK
mode.
Wireless Components
3 - 12
Specification, December 2006