Rainbow Electronics AT86RF211 - Manual (Page 14)

14
AT86RF211
1942C–WIRE–06/02
Figure 16. LC Band-pass Filter
• 10 nF capacitors cut DC response forward and backward.
• The first network has the low cut-off frequency.
• The second network has the high cut-off frequency.
IF2 Amplifier Chain The input impedance of the IF2 amplifier is 1700
Ω
. This value enables the use of popu-
lar filters with impedance between 1500
Ω
and 2000
Ω
. It is directly connected to the FSK
demodulator. The bandwidth is internally limited to 1 MHz to minimize the noise before
the discriminator. It acts like a band pass filter centered at 455 kHz with capacitive cou-
pling between stages of amplifier and mixer. Total voltage gain is typically 86 dB.
Thanks to the capacitive coupling, no slow DC feedback loop is needed enabling a fast
turn on time. IF2DEC has to be decoupled with at least 2.2 nF.
Figure 17. Input of the IF2 Amplifier Schematic
F2
F1
10 nF 10 nF
~ F1 ~ F2
40 kHz or higher
global response
Filter
gain
Frequency
1900 Ω
IF2IN
IF2DEC