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
N
LO2
−
1
N
−
1
=
f
PFD LO2
R N
LO2
N
LO2
(3)
While the following equation is valid for low-side injection:
f
CH
=
f
RO
N
LO2
+
1
N
+
1
=
f
PFD LO2
R N
LO2
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(
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
h-h
h-h
h-h
h-h
h-h
h-h
h-h
f
CH
[kHz]
10
20
25
50
12.5
f
PFD
[kHz]
13.3
26.7
33.3
66.7
16.7
R
Y
R
A
IN
IM
L
E
R
P
750
600
375
300
150
75
30
100
250
133.3
333.3
N
tot
N
)
=
floor(
tot
)
;
A
=
N
tot
−
N
⋅
P
=
N
tot
−
N
⋅
32
P
32
(5)
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
(f
RF
−
f
IF2
)
N
LO2
−
1
f
LO1
=
4
(f
RF
−
2MHz)
3
(6)
f
IF1
=
f
RF
−
N
LO2
f
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. 001
Page 8 of 32
EVB Description
Sept/06
MELEXIS [ Melexis Microelectronic Systems ]
