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CC2550 Datasheet(PDF) 33 Page - Texas Instruments |
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CC2550 Datasheet(HTML) 33 Page - Texas Instruments |
33 / 55 page CC2550 PRELIMINARY Data Sheet (Rev.1.2) SWRS039A Page 33 of 54 interference from other systems operating in the same frequency band. FHSS also combats multipath fading. CC2550 is highly suited for FHSS or multi- channel systems due to its agile frequency synthesizer and effective communication interface. Using the packet handling support and data buffering is also beneficial in such systems as these features will significantly offload the host controller. Charge pump current, VCO current and VCO capacitance array calibration data is required for each frequency when implementing frequency hopping for CC2550. There are 3 ways of obtaining the calibration data from the chip: 1) Frequency hopping with calibration for each hop. The PLL calibration time is approximately 720 µs. 2) Fast frequency hopping without calibration for each hop can be done by calibrating each frequency at startup and saving the resulting FSCAL3 , FSCAL2 and FSCAL1 register values in MCU memory. Between each frequency hop, the calibration process can then be replaced by writing the FSCAL3, FSCAL2 and FSCAL1 register values corresponding to the next RF frequency. The PLL turn on time is approximately 90 µs. 3) Run calibration on a single frequency at startup. Next write 0 to FSCAL3[5:4] to disable the charge pump calibration. After writing to FSCAL3[5:4] strobe SRX (or STX) with MCSM0.FS_AUTOCAL = 1 for each new frequency hop. That is, VCO current and VCO capacitance calibration is done but not charge pump current calibration. When charge pump current calibration is disabled the calibration time is reduced from approximately 720 µs to approximately 150 µs. There is a trade off between blanking time and memory space needed for storing calibration data in non-volatile memory. Solution 2) above gives the shortest blanking interval, but requires more memory space to store calibration values. Solution 3) gives approximately 570 µs smaller blanking interval than solution 1). 26.3 Wideband Modulation not Using Spread Spectrum Digital modulation systems under FCC part 15.247 includes FSK and GFSK modulation. A maximum peak output power of 1 W (+30 dBm) is allowed if the 6 dB bandwidth of the modulated signal exceeds 500 kHz. In addition, the peak power spectral density conducted to the antenna shall not be greater than +8 dBm in any 3 kHz band. Operating at high data rates and high frequency separation, the CC2550 is suited for systems targeting compliance with digital modulation systems as defined by FCC part 15.247. An external power amplifier is needed to increase the output above +1 dBm. 26.4 Data Burst Transmissions The high maximum data rate of CC2550 opens up for burst transmissions. A low average data rate link (e.g. 10 kbps), can be realized using a higher over-the-air data rate. Buffering the data and transmitting in bursts at high data rate (e.g. 500 kbps) will reduce the time in active mode, and hence also reduce the average current consumption significantly. Reducing the time in active mode will reduce the likelihood of collisions with other 2.4 GHz systems, e.g. WLAN. 26.5 Continuous Transmissions In data streaming applications the CC2550 opens up for continuous transmissions at 500 kbps effective data rate. As the modulation is done with an I/Q up-converter with LO I/Q- signals coming from a closed loop PLL, there is no limitation in the length of a transmission. (Open loop modulation used in some transceivers often prevents this kind of continuous data streaming and reduces the effective data rate.) 26.6 Spectrum Efficient Modulation CC2500 also has the possibility to use Gaussian shaped FSK (GFSK). This spectrum-shaping feature improves adjacent channel power (ACP) and occupied bandwidth. In ‘true’ FSK systems with abrupt frequency shifting, the spectrum is inherently broad. By making the frequency shift ‘softer’, the spectrum can be made significantly narrower. Thus, higher data rates can be transmitted in the same bandwidth using GFSK. |
Similar Part No. - CC2550_06 |
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Similar Description - CC2550_06 |
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