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參數(shù)資料
| 型號： | LV2700V |
| 廠商： | Sanyo Electric Co.,Ltd. |
| 英文描述： | Spread Spectrum Communications IC(頻譜擴展通訊芯片) |
| 中文描述： | 擴頻通信集成電路（頻譜擴展通訊芯片） |
| 文件頁數(shù)： | 11/20頁 |
| 文件大小： | 343K |
| 代理商： | LV2700V |
Initial acquisition
In the LV2700V, initial acquisition is done by sliding correlation. Sliding correlation is the method of obtaining the
correlation by shifting, by small amounts at a time, the phase of the receiving side PN code relative to the transmitting
side PN code. The clock of the receiving side PN code generator is being generated by frequency division of the VCO
output similar to the transmitting side. Therefore, a frequency difference is caused between the PN clocks of the
sending and receiving side by slightly shifting the free running frequency from the carrier wave frequency, thereby
carrying out the required sliding. In this case, since the speed of sliding is proportional to the amount of this frequency
shift, making the amount of frequency shift smaller causes the time required for initial capture to become longer. Fig. 5
shows the time between peaks of the autocorrelation function value, etc., during the sliding process.
Fig. 5 The sliding time
Next, let us consider the process up to achieving the initial acquisition. In the sliding process, the output of the
unspreading unit will still be the spread spectrum signal during the period in which the correlation output is zero.
Further, since the carrier wave component is suppressed in the spread wave, the PLL does not operate effectively and
does not get locked, and hence the sliding is continued with the VCO remaining in the free running frequency condition.
Next, in the timing at which a valid autocorrelation output appears, since the continuous carrier wave component appears
in the unspread output, the PLL operates correctly thereby achieving phase synchronization with the carrier wave. As a
result, the VCO output changes from the free running frequency to the carrier wave frequency thereby making the
difference in the transmitting side and receiving side PN clock frequencies zero, and the sliding stop at the point and the
initial acquisition process gets completed.
No. 5651-11/20
LV2700V
Here,
F: VCO Frequency – Carrier frequency
24: Frequency division factor from the VCO output to the PNG clock.
t
A
= 24
PN code length = 3.6 msec @15 chip
F
F = 100 kHz
t
B
= 24
2 = 480 μsec @15 chip
F
F = 100 kHz
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