RFM31B-868-D QUASAR, RFM31B-868-D Datasheet - Page 19

• Manufacturer Part Number: RFM31B-868-D
• Description: MODULE, RECEIVER, -118DB, 868MHZ
• Manufacturer: QUASAR

Specifications of RFM31B-868-D

• Modulation Type: FSK, GFSK, OOK
• Sensitivity: -121dBm
• Power Supply: 1.8V To 3.6V
• Supply Current: 18.5mA
• Data Rate Max: 256Kbps
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.5. Frequency Control
For calculating the necessary frequency register settings it is recommended that custom
These methods offe
application requirements. The following information can be used to calculated these values manually.
3.5.1. Frequency Programming
In order to receive an RF signal,the desired channel frequency,f
that this frequency is the center frequency of the desired channel and not an LO frequency. The carrier frequency
is generated by a Fractional-N Synthesizer, using 10 MHz both as the reference frequency and the clock of the (3
order) ΔΣ modulator. This modulator uses modulo 64000 accumulators. This design was made to obtain the
desired frequency resolution of the synthesizer. The overall division ratio of the feedback loop consist of an integer
part (N) and a fractional part (F). In a generic sense, the output frequency of the synthesizer is as follows:
The fractional part (F) is determined by three different values, Carrier Frequency (fc[15:0]), Frequency Offset
(fo[8:0]), and Frequency Deviation (fd[7:0]). Due to the fine resolution and high loop bandwidth of the synthesizer,
FSK modulation is applied inside the loop and is done by varying F according to the incoming data; this is
discussed further in "3.5.4. Frequency Offset Adjustment ". Also, a
tune the carrier frequency and counteract crystal tolerance errors. For simplicity assume that only the fc[15:0]
register will determine the fractional component. The equation for selection of the carrier frequency is shown
below:
The integer part (N) is determined by fb[4:0]. Additionally, the frequency can be halved by connecting a ÷2 divider
to the output. This divider is not inside the loop and is controlled by the hbsel bit in "Register 75h. Frequency Band
Select." This effectively partitions the entire 240–960 MHz frequency range into two separate bands: High Band
(HB) for hbsel = 1, and Low Band (LB) for hbsel = 0. The valid range of fb[4:0] is from 0 to 23. If a higher value is
written into the register, it will default to a value of 23. The integer part has a fixed offset of 24 added to it as shown
in the formula above. Table 11 demonstrates the selection of fb[4:0] for the corresponding frequency band.
After selection of the fb (N) the fractional component may be solved with the following equation:
fb and fc are the actual numbers stored in the corresponding registers.
HOPERF Register
Add R/W Function/Description
73
74
75
76
77
Tel: [phone]
R/W
R/W
R/W Frequency Band Select Reserved
R/W
R/W
Frequency Offset 1
Frequency Offset 2
Nominal Carrier
Nominal Carrier
Frequency 1
Frequency 0
Calculator worksheet (in Microsoft Excel) available on
r a simple method to quickly determine the correct settings based on the
fc
Fax: [phone]
f
[
15
carrier
:
] 0
Reserved Reserved Reserved Reserved Reserved Reserved fo[9] fo[8]

fc[15]

10
fo[7]
fc[7]
f
D7
carrier

 

MHz
10
MHz

f
( *
OUT
10
fc[14]
sbsel
fo[6]
fc[6]
hbsel
D6
f
MHz
( *
carrier

hbsel
10

MHz

E-mail: [e-mail] http://www.hoperf.com
) 1
(
hbsel
fc[13]
fo[5]
fc[5]
hbsel
( *
D5

) 1

fb
(

[
N
: 4

carrier
fb
) 1

fc[12]
] 0
[
fo[4]
fb[4]
fc[4]
D4
: 4
F

, must be programmed into the RFM31B.Note

(
)
] 0
N
24
fixed



24
the product website.
F
fc[11]
fc
fo[3]
fb[3]
fc[3]
)
64000
D3

 

[
15
*
offset can
64000
:
] 0
)
fc[10]
fo[2]
fb[2]
fc[2]
D2
ers use
be
fo[1] fo[0]
fb[1] fb[0]
fc[9] fc[8]
fc[1] fc[0]
D1
RFM31B
added
D0 POR Def.
to fine-
BBh
00h
00h
35h
80h
19
rd