RFM42B-868-S1 QUASAR, RFM42B-868-S1 Datasheet - Page 18

• Manufacturer Part Number: RFM42B-868-S1
• Description: MODULE, TRANSMITTER, 20DB,SMD,868MHZ
• Manufacturer: QUASAR

Specifications of RFM42B-868-S1

• Modulation Type: FSK, GFSK, OOK
• Supply Voltage Range: 1.8V To 3.6V
• Supply Current: 85mA
• Interface Type: SPI
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

RFM42B/43B
3.5. Frequency Control
For calculating the necessary frequency register settings it is recommended that customers use
application requirements. The following information can be used to calculated these values manually.
3.5.1. Frequency Programming
In order to transmit an RF signal, the desired channel frequency, f
RFM42B/43B . Note that this frequency is the center frequency of the desired channel. 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 Deviation" . Also, a fixed offset can be added to fine-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 output 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.
18
Add R/W Function/Description
the HOPERF Register Calculator worksheet (in Microsoft Excel) available on
These methods offe
73
74
75
76
77
Tel: [phone]
R/W
R/W
R/W Frequency Band Select
R/W
R/W
Frequency Offset 1
Frequency Offset 2
Nominal Carrier
Nominal Carrier
Frequency 1
Frequency 0
r a simple method to quickly determine the correct settings based on the
fc
f
[
15
TX
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
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10

fc[15]
fo[7]
fc[7]
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carrier
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10
MHz
( *

f
OUT
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hbsel
fc[14]
sbsel
fo[6]
fc[6]
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hbsel
fc[13]
fo[5]
fc[5]
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fb
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[
(
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fc[12]
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fb[4]
fc[4]
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24
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24
F
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fo[3]
fb[3]
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15
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fc[10]
fo[2]
fb[2]
fc[2]
D2
fo[1] fo[0]
fo[9] fo[8]
fb[1] fb[0]
fc[9] fc[8]
fc[1] fc[0]
D1
D0 POR Def.
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