micrf405 Micrel Semiconductor, micrf405 Datasheet - Page 30

• Manufacturer Part Number: micrf405
• Description: Micrf405 290mhz To 980mhz Ism Band Ask/fsk Transmitter
• Manufacturer: Micrel Semiconductor

April 2006
Bit Rate Settings
The bit rate is set separately for ASK and FSK
modulation to support ASK modulation with FSK
spreading. The FSK bit rate is set with the two
parameters FSKClk_K and FSKn . The relationship is
A procedure to find the settings for the desired bit
rate is described below:
In some cases, several combinations of FSKClk_K
and FSKn will give the bit rate. If VCO modulation is
selected, Modulation[1:0] < 2, then the lower FSKn
Modulator
Micrel
0001110
0001111
0010000
1. Set FSKn to 0.
2. Calculate FSKClk_K by using this formula:
3. If FSKClk_K is too high, increment FSKn by
A6..A0
where:
BR: Bit rate.
fXTAL: Crystal oscillator frequency.
FSKClk_K: Integer in the range [1..63] (6 bit).
FSKn: Integer in the range [0..5] (3 bit).
BR
Adr
one, and then jump to 2.
FSKClk
=
FSKClk
VCO_Fr_Chk=0
MOD_TEST1=0
Mod_I4=0
_
D7
K
f
_
XTAL
K
=
⋅
BR
2
3
VCO_Fr_Auto=0
Prescaler_Sel=0
+
f
⋅
FSKn
XTAL
2
Mod_I3=1
3
+
D6
FSKn
FSKClk_K5=1
Mod_I2=0
FSKn2=1
Figure 15. Modulator Block Diagram.
D5
(1)
FSKClk_K4=1
Mod_I1=0
FSKn1=0
D4
30
Data
the better shaping of the signal. However in some
cases, low FSKn causes the modulator to saturate
(Please see the section Modulator for details). When
Manchester encoding is enabled, Manchester_en=1,
FSKn needs to bigger than zero for the modulator to
operate properly.
When sending ASK with FSK spreading, FSKClk_K
and FSKn set the speed of the FSK spreading.
The bit rate of the ASK is set similar with the two
parameters ASKClk_K and ASKn. The relationship
is now:
A procedure for finding a bit rate will be equal to
FSK, but with this formula:
Due to the high flexibility of the modulator, a brief
explanation of how it works will ease the use of it.
Figure 15 shows a block diagram of the components
of the modulator.
where the new parameters are:
ASKClk_K: Integer in the range [1..63] (6 bits).
ASKn: Integer in the range [0..3] (2 bits).
FSKClk_K3=0
BR
ASKClk
Mod_I0=1
FSKn0=0
D3
=
ASKClk
_
K
=
FSKClk_K2=1
f
Mod_A2=0
Mod_F2=1
_
BR
XTAL
K
D2
⋅
⋅
f
XTAL
2
2
5
5
+
+
ASKn
ASKn
FSKClk_K1=0
Mod_A1=1
Mod_F1=0
D1
MICRF405
FSKClk_K0=0
[phone]
M9999-041906
Mod_A0=1
Mod_F0=0
D0
(2)