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SI4020 参数 Datasheet PDF下载

SI4020图片预览
型号: SI4020
PDF下载: 下载PDF文件 查看货源
内容描述: 完全集成( IOW BOM ,易于设计的)无生产快速稳定所需的对齐方式,可编程,高清晰度PLL [Fully integrated (Iow BOM, easy design-in) No alignment required in production Fast settling, programmable, high-resolution PLL]
分类和应用:
文件页数/大小: 32 页 / 1064 K
品牌: SILICON [ SILICON ]
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Si4020  
Wake-Up Timer  
DETAILED DESCRIPTION  
The Si4020 FSK transmitter is designed to cover the unlicensed  
frequency bands at 315, 433, 868, and 915 MHz. The device  
facilitates compliance with FCC and ETSI requirements.  
The wake-up timer has very low current consumption (1.5 uA  
typical) and can be programmed from 1 ms to several days with  
an accuracy of ±5%.  
It calibrates itself to the crystal oscillator at every startup. When  
the oscillator is switched off, the calibration circuit switches on  
the crystal oscillator only long enough for a quick calibration (a  
few milliseconds) to facilitate accurate wake-up timing.  
PLL  
The programmable PLL synthesizer determines the operating  
frequency, while preserving accuracy based on the on-chip  
crystal-controlled reference oscillator. The PLL’s high resolution  
allows the usage of multiple channels in any of the bands. The  
FSK deviation is selectable (from 30 to 240 kHz with 30 kHz  
increments) to accommodate various bandwidth, data rate and  
crystal tolerance requirements, and it is also highly accurate due  
to the direct closed-loop modulation of the PLL. The transmitted  
digital data can be sent asynchronously through the FSK pin or  
over the control interface using the appropriate command.  
Event Handling  
In order to minimize current consumption, the device supports  
sleep mode. Active mode can be initiated by several wake-up  
events: timeout of wake-up timer, detection of low supply  
voltage, pressing any of the four push-button inputs, or through  
the serial interface. The push-button inputs can be driven by a  
logic signal from a microcontroller or controlled directly by  
normally open switches. Pull-up resistors are integrated.  
The RF VCO in the PLL performs automatic calibration, which  
requires only a few microseconds. To ensure proper operation in  
the programmed frequency band, the RF VCO is automatically  
calibrated upon activation of the synthesizer. If temperature or  
supply voltage change significantly or operational band has  
changed, VCO recalibration is recommended.. Recalibration can  
be initiated at any time by switching the synthesizer off and back  
on again.  
If any wake-up event occurs, the wake-up logic generates an  
interrupt, which can be used to wake up the microcontroller,  
effectively reducing the period the microcontroller has to be  
active. The cause of the interrupt can be read out from the  
transmitters by the microcontroller through the nIRQ pin.  
Interface  
An SPI compatible serial interface lets the user select the  
operating frequency band and center frequency of the  
synthesizer, polarity and deviation of FSK modulation, and output  
power level. Division ratio for the microcontroller clock, wake-up  
timer period, and low battery detector threshold are also  
programmable. Any of these auxiliary functions can be disabled  
when not needed. All parameters are set to default after power-  
on; the programmed values are retained during sleep mode.  
RF Power Amplifier (PA)  
The power amplifier has an open-collector differential output and  
can directly drive a loop antenna with a programmable output  
power level. An automatic antenna tuning circuit is built in to  
avoid costly trimming procedures and the so-called “hand effect.”  
The transmitters can operate in On-Off Keying (OOK) mode by  
switching the power amplifier on and off. When the appropriate  
control bit is set using the Power Setting Command, the FSK pin  
becomes an enable input (active high) for the power amplifier.  
EEPROM Mode  
In simple applications, the on-chip digital controller provides the  
transmitters with direct interface to a serial (SPI) EEPROM. In this  
case, no external microcontroller is necessary. Wake-up events  
initiate automatic readout of the assigned command sequence  
from EEPROM memory. For every event, there is a dedicated  
starting address available in the EEPROM.  
Crystal Oscillator  
The chip has a single-pin crystal oscillator circuit, which provides  
a 10 MHz reference signal for the PLL. To reduce external parts  
and simplify design, the crystal load capacitor is internal and  
programmable. Guidelines for selecting the appropriate crystal  
can be found later in this datasheet.  
Programming the EEPROM is very simple. Any control command  
can be programmed in the EEPROM sequentially (same as in  
microcontroller mode).  
The transmitters can supply the clock signal for the  
microcontroller, so accurate timing is possible without the need  
for a second crystal. When the chip receives a Sleep Command  
from the microcontroller and turns itself off, it provides several  
further clock pulses (“clock tail”) for the microcontroller to be  
able to go to idle or sleep mode. The length of the clock tail is  
programmable.  
The internal power-on reset (POR) is a dedicated event, which  
can be used to program the basic settings of the transmitters. In  
this case the chip starts to read out the preprogrammed data  
from the 00h address in EEPROM. Data can be transmitted with  
the help of the Data Transmit Command, which tells the  
transmitters how many bytes must be transmitted. The whole  
process finishes with a Sleep Command.  
Low Battery Voltage Detector  
The low battery voltage detector circuit monitors the supply  
voltage and generates an interrupt if it falls below  
a
programmable threshold level. The detector circuit has 50 mV  
hysteresis.  
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