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| 型号： | RFPIC12F675K-E/SS |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, FLASH, 20 MHz, RISC MICROCONTROLLER, PDSO20 |
| 封装： | 0.209 INCH, PLASTIC, MO-150, SSOP-20 |
| 文件页数： | 73/123页 |
| 文件大小： | 5438K |
| 代理商： | RFPIC12F675K-E/SS |
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2003 Microchip Technology Inc.
Preliminary
DS70091A-page 51
rfPIC12F675
9.5
FSK Modulation
In FSK modulation the transmit data is sent by varying
the output frequency. This is done by loading the
reference crystal with extra capacitance to pull it to a
slightly lower frequency which the PLL then tracks.
Switching the capacitance in and out with the data
signal toggles the transmitter between two frequencies.
These
two
crystal
based
frequencies
are
then
multiplied by 32 for the RF transmit frequency.
Unlike the ASK transmit frequency the FSK center
frequency is not actually transmitted. It is the artificial
point
half
way
between
the
two
transmitted
frequencies, calculated with this formula.
The other important parameter in FSK is the frequency
deviation of the transmit frequency. This measures how
far the frequency will swing from the center frequency.
Single ended deviation is calculated with this formula.
An FSK receiver will specify its optimal value of
deviation. The single ended deviation must be greater
than data rate/4. The minimum deviation is usually
limited by the frequency accuracy of the transmitter and
receiver components. The maximum deviation is usually
limited by the pulling characteristics of the transmitter
crystal.
An extra capacitor and the internal switch are added to
the ASK design to build an FSK transmitter as shown
in Figure 9-3. The C1 capacitor in series with the crystal
determines the maximum frequency.
With the DATA
FSK pin high the FSKOUT pin is open and
the C2 capacitor does not affect the frequency. When
the DATA
FSK pin goes low, FSKOUT shorts to ground,
and the C2 is thrown in parallel with C1. The sum of the
two caps pulls the oscillation frequency lower as shown
in Figure 9-4.
In FSK mode the DATA
ASK pin should be tied high to
enable the PA. The FSK circuit is shown in Figure 9-6.
Use accurate crystals for narrow bandwidth systems
and large values for C1 to reduce frequency drift.
FIGURE 9-3:
FSK CRYSTAL CIRCUIT
FIGURE 9-4:
FREQUENCY PULLING
TABLE 9-3:
TYPICAL TRANSMIT CENTER FREQUENCY AND DEVIATION (FSK MODE) (1)
2
min
max
f
fc
+
=
2
min
max
f
=
XTAL
rfPIC12F675K/F/H
X1
C1
C2
FSKOUT
Frequency
(MHz)
Fmax
Fmin
C1
C1||C2
DATAFSK = 1 DATAFSK = 0
Load Capacitance (pF)
C2 = 1000 pF
C2 = 100 pF
C2 = 47 pF
C1 (pF)
Freq (MHz) / Dev (kHz)
22
433.612 / 34
433.619 / 27
433.625 / 21
33
433.604 / 25
433.610 / 19
433.614 / 14
39
433.598 / 20
433.604 / 14
433.608 / 10
47
433.596 / 17
433.601 / 11.5
433.604 / 8
68
433.593 / 13
433.598 / 9
433.600 / 5.5
100
433.587 / 8
—
Note 1: Standard Operating Conditions, T
A = 25°C, RFEN = 1, VDDRF = 3V, fXTAL = 13.55 MHz
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| RFPIC12F675K-I/SS | 功能描述:射频微控制器 - MCU 290-350MHz UHF ASK/FSK Transmitter RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:Si100x 数据总线宽度:8 bit 最大时钟频率:24 MHz 程序存储器大小:64 KB 数据 RAM 大小:4 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 85 C 封装 / 箱体:LGA-42 安装风格:SMD/SMT 封装:Tube |
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