EVB71122_15 Datasheet, PDF (9/31 Pages) Melexis Microelectronic Systems – 300 to 930MHz Receiver Evaluation Board Description

EVB71122
300 to 930MHz Receiver
Evaluation Board Description
Due to the double superhet receiver architecture, the channel frequency step size f_CH is not equal to the
phase-frequency detector (PFD) frequency f_PFD. For high-side injection, the channel step size f_CH is given by:
f_CH

f _RO
R
N _LO2 
N _LO2
1

f
PFD
N _LO2  1
N _LO2
(3)
While the following equation is valid for low-side injection:
f_CH

f _RO
R
N _LO2 
N _LO2
1

f
PFD
N _LO2  1
N _LO2
(4)
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 f_RF and the channel step size f_CH are given by system requirements. The N and
A counter settings can be derived from N_tot or f_LO1 and f_PFD by using the following equations.
N

floor( ^Ntot )
P

floor( ^{N tot} )
32
;
A

N _tot

NP

N _tot

N  32
(5)
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 f_PFD
according to below table. The R counter values are valid for a 10MHz crystal reference frequency f_RO. The
PFD frequency is given by f_PFD = f_RO /R.
Injection Type
f_CH [kHz]
f_PFD [kHz]
R
h-h
10
13.3
750
h-h
12.5
16.7
600
h-h
20
26.7
375
h-h
25
33.3
300
h-h
50
66.7
150
h-h
100
133.3
75
h-h
250
333.3
30
The second step is to calculate the missing parameters f_LO1, f_IF1, N_tot, N and A. While the second IF (f_IF2), the
N_LO2 divider ratio and the prescaler divider ratio P are bound to f_IF2 = 2MHz, N_LO2 = 4 (or 8) and P =32.
f _LO1

N _LO2
N _LO2 
1
(f
RF
 f_IF2 )
f _LO1

4
3
(f _RF

2M Hz)
(6)
f _IF1

f _RF  N _LO2f_IF2
N _LO2  1
f _IF1

f _RF
 8MHz
3
(7)
Finally N and A can be calculated with formula (5).
39012 71122 01
Rev. 005
Page 9 of 31
EVB Description
Nov/15