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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： | 72/123页 |
| 文件大小： | 5438K |
| 代理商： | RFPIC12F675K-E/SS |
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rfPIC12F675
DS70091A-page 50
Preliminary
2003 Microchip Technology Inc.
9.3
Crystal Oscillator
The transmitter crystal oscillator is a Colpitts oscillator
that provides the reference frequency to the PLL. It is
independent of the microcontroller oscillator. An
external crystal or AC coupled reference signal is
connected to the XTAL pin. The transmit frequency is
fixed
and
determined
by
the
crystal
frequency
according to the formula:
Due to the flexible selection of transmit frequency, the
resulting crystal frequency may not be a standard off-
the-shelf value. Therefore, for some carrier frequencies
the designer will have to consult a crystal manufacturer
and
have
a
custom
crystal
manufactured.
For
background information on crystal selection see
Application Note AN588, PICmicro Microcontroller
Oscillator Design Guide, and AN826 Crystal Oscillator
Basics
and
Crystal
Selection
for
rfPIC
and
PICmicro Devices.
For ASK modulation the crystal can be connected
directly from RFXTAL to ground, or in series with an
additional capacitor to trim the frequency. Figure 9-2
shows how the crystal is connected and Table 9-2
shows how the frequency of a typical crystal changes
with capacitance.
The oscillator is enabled when the RFEN input is high.
It takes the crystal approximately 1 ms to start oscillat-
ing. Higher frequency crystals start-up faster than
lower frequencies. The crystal oscillator start time
(T
ON) is listed in Table 13-11, Transmitter AC
Characteristics. This start-up time is mainly due to the
crystal building up an oscillation, but also includes the
time for the PLL to lock on the crystal frequency.
9.4
ASK Modulation
In ASK modulation the data is transmitted by varying
the output power. The DATA
ASK pin enables the PA,
toggling the pin turns the RF output signal on and off. A
simple receiver using a tuned filter and peak detector
diode can capture the data. A more advanced super-
heterodyne receiver such as the rfRXD0420 can
greatly increase the range and reduce susceptibility to
interference.
In ASK mode the DATA
FSK and FSKOUT pins are not
used and should both be tied to ground. An example of
a typical ASK circuit is shown in Figure 9-5. The C1
capacitor can be replaced by a short to simplify the
transmitter if the receiver has a wide enough
bandwidth. For a very narrowband receiver the C1
capacitor may need to be replaced by a trimmer cap to
tune the transmitter to the exact frequency.
FIGURE 9-2:
ASK CRYSTAL CIRCUIT
TABLE 9-2:
XTAL OSC APPROXIMATE FREQ. VS. CAPACITANCE (ASK MODE) (1)
32
×
=
RFXTAL
transmit
f
XTAL
rfPIC12F675K/F/H
X1
C1
Predicted Frequency
(MHz)
PPM from 13.55 MHz
Transmit Frequency (MHz)
(32 * f
XTAL)
22 pF
13.551438
+106
433.646
39 pF
13.550563
+42
433.618
100 pF
13.549844
-12
433.595
150 pF
13.549672
-24
433.5895
470 pF
13.549548
-33
433.5856
1000 pF
13.549344
-48
433.579
Note 1: Standard Operating Conditions (unless otherwise stated) T
A = 25°C, RFEN = 1, VDDRF = 3V,
f
XTAL = 13.55 MHz
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| RFPIC12F675KT-I/SS | 功能描述:射频微控制器 - MCU 1 KB Flash FSK ASK 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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