EVB71122
300 to 930MHz Receiver
Evaluation Board Description
Due to the double superhet receiver architecture, the channel frequency step size fCH is not equal to the
phase-frequency detector (PFD) frequency fPFD. For high-side injection, the channel step size fCH is given by:
fRO NLO2 −1
NLO2 −1
NLO2
fCH
=
= fPFD
(3)
(4)
R
NLO2
While the following equation is valid for low-side injection:
fRO NLO2 +1
NLO2 +1
NLO2
fCH
=
= fPFD
R
NLO2
2.2 Calculation of Counter Settings
Frequency planning and the selection of the MLX71122’s PLL counter settings are straightforward and can
be laid out on the following procedure.
Usually the receive frequency fRF and the channel step size fCH are given by system requirements. The N
and A counter settings can be derived from Ntot or fLO1 and fPFD by using the following equations.
N
N
N = floor( tot ) = floor( tot ) ; A = Ntot − N ⋅ P = Ntot − N ⋅32
32
(5)
P
2.2.1
Calculation of LO1 and IF1 frequency for Low Frequency Bands
High-high injection must be used for the low frequency bands. First of all choose a PFD frequency fPFD
according to below table. The R counter values are valid for a 10MHz crystal reference frequency fRO. The
PFD frequency is given by fPFD = fRO /R.
Injection Type
fCH [kHz]
10
fPFD [kHz]
13.3
R
h-h
h-h
h-h
h-h
h-h
h-h
h-h
750
600
375
300
150
75
12.5
20
16.7
26.7
25
33.3
50
66.7
100
250
133.3
333.3
30
The second step is to calculate the missing parameters fLO1, fIF1, Ntot, N and A. While the second IF (fIF2), the
NLO2 divider ratio and the prescaler divider ratio P are bound to fIF2 = 2MHz, NLO2 = 4 (or 8) and P =32.
NLO2
4
fLO1
=
(fRF − fIF2 )
fLO1 = (fRF − 2MHz)
(6)
(7)
NLO2 −1
3
fRF − NLO2fIF2
NLO2 −1
fRF − 8MHz
fIF1
=
fIF1 =
3
Finally N and A can be calculated with formula (5).
39012 71122 01
Rev. 001
Page 8 of 32
EVB Description
Sept/06
MELEXIS [ Melexis Microelectronic Systems ]
