AT86RF211SAHW Atmel, AT86RF211SAHW Datasheet - Page 15

• Manufacturer Part Number: AT86RF211SAHW
• Manufacturer: Atmel

Specifications of AT86RF211SAHW

• Lead Free Status / Rohs Status: Compliant

4.2.5
4.2.6
e2v semiconductors SAS 2008
IF1 Filtering
IF1 Gain and Second Mixer
The first mixer translates the input RF signal down to 10.7 MHz.
The local oscillator is provided by the same synthesizer that generates a local frequency 10.7 MHz away
from the Tx carrier frequency.
The output impedance of the mixer is 330Ω with a 20% accuracy, so that low-cost, standard 10.7 MHz
ceramic filters can be directly driven. Other IFs may be chosen thanks to the mixer’s high bandwidth
(50 MHz).
A popular ceramic filter is used to reject the second image frequency and provide a first level of filtering.
The IF1 filter can be removed however; it leads to a sensitivity reduction of about 3 dB (the substitution
coupling capacitor should be greater than 100 pF).
The input impedance of the IF1 amplifier is naturally 330Ω to match the input filter. The voltage gain, that
is the gain at 10.7 MHz added to the conversion gain at 455 kHz, is typically 14 dB when loaded with
1700Ω. The second mixer operates at a fixed LO frequency of 10.245 MHz. Its output impedance is
1700Ω in parallel to 20 pF.
Figure 4-9.
Figure 4-10. Schematic Input of the IF1 Amplifier
IF1 Filtering
330 Ω
IF1OUT
(pin 36)
IF1DEC
IF1IN
C > 100 pF
IF1
330 Ω
"or"
20 k Ω
(pin 35)
IF1IN
330 Ω
0894C–WIRE–11/08
AT86RF211S
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