Rainbow-electronics AT86RF211 User Manual download pdf (Page 11)

AT86RF211

1942C–WIRE–06/02

Figure 10. TEM Filter

Such a filter also provides an out-of-band interference rejection greater than 20dB,

40MHzawayfrom433MHz.

First LNA/Mixer The main characteristics of the LNA/Mixer are typically:

• Voltage gain: 17 dB for the LNA/Mixer; 11 dB if gain min. is selected

• Bandwidth: 1.2 GHz

• Noise figure of LNA alone: 3 dB at 900 MHz, best matching

• Noise figure of LNA + mixer:

8 dB at 900 MHz, with maximum gain and best matching

12 dB at 900 MHz, with minimum gain and best matching

• 1 dB compression point: -20 dBm at the input of LNA

• Matching:

Notes: 1. RXIN: impedance to be seen by LNA input for NF optimization purpose

2. SWOUT: output impedance of the RF switch

The gain is programmable through bit 25 of CTRL1 register (6dB attenuation when min

gain is selected). The choice for the matching between the SWITCH and the LNA

depends mainly on the chosen SAW filter. Usually in/out impedance of SAW filters is

50Ω, but other ones can be implemented and the matching network recalculated thanks

to the previous impedance table.

The LNA is directly coupled to the first mixer. Input and output of the LNA/Mixer must be

connected through a capacitive link because of their internal DC coupling. A SAW or

ceramic filter provides such a link.

1 pF

Zc = 7Ω

l = 0.75

(19 mm)

TEM

Table 2. Matching Information

Frequency Band RXIN

(1)

SWOUT

(2)

433 MHz 35 + j 170Ω 24 - j 43Ω

868 MHz 37 + j 85Ω 50 - j 42Ω

915 MHz 30 + j 85Ω 50 - j 42Ω

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 47 48

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Rainbow-electronics AT86RF211 User Manual Page 11