MLX71120_12 Datasheet, PDF (15/31 Pages) Melexis Microelectronic Systems – FSK/FM/ASK Receiver

MLX71120
300 to 930MHz
FSK/FM/ASK Receiver
2.1 Calculation of Frequency Settings
The receiver has two predefined receive frequency plans which can be selected by the RFSEL control pin.
Depending on the logic level of RFSEL pin the sideband selection of the second mixer and the counter set-
tings for N1 and N2 are changed accordingly.
RFSEL
Injection
f_RFmin [MHz]
f_RFmax [MHz]
N₁
N₂
0
high-low
300
470
4
6
1
low-high
610
930
2
12
The following table shows the relationships of several internal receiver frequencies for the two input fre-
quency ranges.
f_RF [MHz]
f_IF1
f_LO1
f_LO2
f_RO
300 to 470
f _RF + N₁f _IF2
N₁ −1
N₁ (f _RF + f _IF2 )
N₁ −1
f _RF + f _IF2
N₁ −1
f _RF + f _IF2
N₂ (N₁ − 1)
610 to 930
f _RF − N₁f _IF2
N₁ +1
N₁ (f _RF + f _IF2 )
N₁ +1
f _RF + f _IF2
N₁ +1
f _RF + f _IF2
N₂ (N₁ + 1)
Given IF2 is selectable at either 455kHz or 10.7MHz and the corresponding N₁, N₂ counter settings, above
equations can be transferred into the following table.
IF2=455kHz
f_RF [MHz]
300 to 470
610 to 930
f_IF1
f _RF + 1.82MHz
3
f_RF − 0.91MHz
3
f_LO1
4(f _RF + 0.455MHz)
3
2(f _RF + 0.455MHz)
3
f_LO2
f_RF + 0.455MHz
3
f_RO
f_RF + 0.455MHz
18
f_RF + 0.455MHz
36
IF2=10.7MHz
f_RF [MHz]
300 to 470
610 to 930
f_IF1
f _RF + 42.8MHz
3
f_RF − 21.4MHz
3
f_LO1
4(f_RF + 10.7MHz)
3
2(f_RF + 10.7MHz)
3
f_LO2
f_RF + 10.7MHz
3
f_RO
f_RF + 10.7MHz
18
f_RF + 10.7MHz
36
39010 71120
Rev. 008
Page 15 of 31
Data Sheet
Jun/12