4432-T-B1 B 915【PDF 25/47 页】KIT DEV TEST EZRADIOPRO SI4432

Si4430/31/32-B1

Rev 1.1

25

3.5. Frequency Control

For calculating the necessary frequency register settings it is recommended that customers use Silicon Labs

Wireless Design Suite (WDS) or the EZRadioPRO Register Calculator worksheet (in Microsoft Excel) available on

the product website. These methods offer a simple method to quickly determine the correct settings based on the

application requirements. The following information can be used to calculated these values manually.

3.5.1. Frequency Programming

In order to receive or transmit an RF signal, the desired channel frequency, f

carrier

, must be programmed into the

Si4430/31/32. The Si4431/32 and Si4430 cover different frequencies. This section discusses the frequency range

covered by all EZRadioPRO devices. Note 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

rd

order) 敚 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" on page 27. 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 ?

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 240960 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 12 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.

Add R/W Function/Description

D7

D6

D5

D4

D3

D2

D1

D0 POR Def.

73 R/W

Frequency Offset 1

fo[7]

fo[6]

fo[5]

fo[4]

fo[3]

fo[2]

fo[1] fo[0]

00h

74 R/W

Frequency Offset 2

fo[9] fo[8]

00h

75 R/W Frequency Band Select

sbsel

hbsel

fb[4]

fb[3]

fb[2]

fb[1] fb[0]

35h

76 R/W

Nominal Carrier

Frequency 1

fc[15]

fc[14]

fc[13]

fc[12]

fc[11]

fc[10]

fc[9] fc[8]

BBh

77 R/W

Nominal Carrier

Frequency 0

fc[7]

fc[6]

fc[5]

fc[4]

fc[3]

fc[2]

fc[1] fc[0]

80h

)

(

10

F

N

MHz

OUT

)

(

)

1

(

10

F

N

hbsel

MHz

carrier

)

64000

]

0

:

15

[

24

]

0

:

4

[

(

*

)

1

(

*

10

fc

fb

hbsel

MHz

TX

+

=

64000

*

24

]

0

:

4

[

)

1

(

*

10

]

0

:

15

[

?/DIV>

-

+

=

fb

hbsel

MHz

f

fc

TX

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