TDA7210V_10 Datasheet, PDF (25/44 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA7210V
Applications
3.6.2 ASK Mode
In case the receiver is operated in ASK mode the datapath frequency charactersitic is dominated by the data filter
alone, thus it is lowpass shaped.The cutoff frequency is determined by the external capacitors C12 and C14 and
the internal 100k resistors as described in Chapter 3.2.
0dB
-3dB
-40dB/dec
f
f3dB
Figure 13 Frequency Charcteristic in Case of ASK Mode
3.7
Principle of the Precharge Circuit
In case the data slicer threshold shall be generated with an external RC network as described in Chapter 3.5 it is
necessary to use large values for the capacitor C13 attached to the SLN pin (pin 19) in order to achieve long time
constants. This results also from the fact that the choice of the value for R1 connected between the SLP and SLN
pins (pins 18 and 19) is limited by the 330 kΩ resistor appearing in parallel to R1 as can be seen in Figure 11.
Apart from this a resistor value of 100 kΩ leads to a voltage offset of 1mV at the comparator input as described in
Chapter 3.6.1. The resulting startup time constant t1 can be calculated with:
τ ₁ = (R1 || 330 kΩ )× C13
(13)
In case R1 is chosen to be 100 kΩ and C13 is chosen as 47 nF this leads to
τ₁ = (100kΩ || 330kΩ)× 47nF = 77kΩ × 47nF = 3.6ms
(14)
When the device is turned on this time constant dominates the time necessary for the device to be able to
demodulate data properly. In the powerdown mode the capacitor is only discharged by leakage currents.
In order to reduce the turn-on time in the presence of large values of C13 a precharge circuit was included in the
TDA7210V as shown in the following figure.
Data Sheet
25
Revision 1.1, 2010-06-18