TDA5211 Datasheet, PDF (29/52 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA 5211
Applications
This offset voltage is generated by the bias current of the negative input of the
comparator (i.e. 20nA) running over the external resistor R. This voltage raises
the voltage appearing at pin 20 (e.g. 1mV with R = 100kΩ). In order to obtain
benefit of this asymmetrical offset for the demodulation of long zeros the lower
of the two FSK frequencies should be chosen in the transmitter as the zero-
symbol frequency.
In the following figure the shape of the above mentioned bandpass is shown.
gain (pin19)
v
v-3dB
3dB
0dB
DC
20dB/dec
f1
f2
-40dB/dec
f
f3
0.18mV/kHz
2mV/kHz
Figure 4-8 Frequency characterstic in case of FSK mode
frequenzgang.WMF
The cutoff frequencies are calculated with the following formulas:
f₁ =
2π
1
R ⋅330kΩ _⋅C
R + 330kΩ
f₂ = v ⋅ f₁ =11⋅ f₁
f₃ = f_3dB
f₃ is the 3dB cutoff frequency of the data filter - see Section 4.2.
Example:
R = 100kΩ, C = 47nF
This leads tof₁ = 44Hz and f₂ = 485Hz
Wireless Components
4-9
Specification, May 2001