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SP000012902 View Datasheet(PDF) - Infineon Technologies

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SP000012902
Infineon
Infineon Technologies Infineon
SP000012902 Datasheet PDF : 38 Pages
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3.4
Functional Blocks
TDA 5201
ASK Single Conversion Receiver
Functional Description
3.4.1 Low Noise Amplifier (LNA)
The LNA is an on-chip cascode amplifier with a voltage gain of 15 dB to 20 dB. The gain figure is determined by
the external matching networks situated ahead of LNA and between the LNA output LNO (Pin 6) and the Mixer
Inputs MI and MIX (Pin 8 and Pin 9). The noise figure of the LNA is approximately 2 dB, the current consumption
is 500 µA. The gain can be reduced by approximately 18 dB. The switching point of this AGC action can be
determined externally by applying a threshold voltage at the THRES pin (Pin 23). This voltage is compared
internally with the received signal (RSSI) level generated by the limiter circuitry. In case that the RSSI level is
higher than the threshold voltage the LNA gain is reduced and vice versa. The threshold voltage can be generated
by attaching a voltage divider between the 3VOUT pin (Pin 24) which provides a temperature stable 3 V output
generated from the internal bandgap voltage and the THRES pin as described in Chapter 4.1. The time constant
of the AGC action can be determined by connecting a capacitor to the TAGC pin (Pin 4) and should be chosen
along with the appropriate threshold voltage according to the intended operating case and interference scenario
to be expected during operation. The optimum choice of AGC time constant and the threshold voltage is described
in Chapter 4.1.
3.4.2 Mixer
The Double Balanced Mixer down-converts the input frequency (RF) in the range of 310 MHz to 350 MHz to the
intermediate frequency (IF) at 10.7 MHz with a voltage gain of approximately 21 dB by utilizing either high- or low-
side injection of the local oscillator signal. In case the mixer is interfaced only single-ended, the unused mixer input
has to be tied to ground via a capacitor. The mixer is followed by a low pass filter with a corner frequency of 20 MHz
in order to suppress RF signals to appear at the IF output (IFO pin). The IF output is internally consisting of an
emitter follower that has a source impedance of approximately 330 to facilitate interfacing the pin directly to a
standard 10.7 MHz ceramic filter without additional matching circuitry.
3.4.3 PLL Synthesizer
The Phase Locked Loop synthesizer consists of a VCO, an asynchronous divider chain, a phase detector with
charge pump and a loop filter and is fully implemented on-chip. The VCO is including spiral inductors and varactor
diodes. The FSEL pin (Pin 11) has to be left open. The tuning range of the VCO was designed to guarantee over
production spread and the specified temperature range a receive frequency range between 310 MHz and
350 MHz depending on whether high- or low-side injection of the local oscillator is used. The oscillator signal is
fed both to the synthesizer divider chain and to a divider that is dividing the signal by 2 before it is applied to the
down-converting mixer. Local oscillator high side injection has to be used for receive frequencies between
approximately 310 MHz and 330 MHz, low side injection for receive frequencies between 330 MHz and 350 MHz
- see also Chapter 4.4.
3.4.4 Crystal Oscillator
The on-chip crystal oscillator circuitry allows for utilization of quartzes both in the 5 MHz and 10 MHz range as the
overall division ratio of the PLL can be switched between 64 and 128 via the CSEL (Pin 16) pin according to the
following table.
Table 2 CSEL Pin Operating States
CSEL
Open
Shorted to ground
Crystal Frequency
5.xx MHz
10.xx MHz
Data Sheet
19
Revision 1.6, 2010-12-21
 

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