參數(shù)資料
型號： B900J24FXX12IT
元件分類： 數(shù)字信號處理
英文描述： 0-BIT, 59.88 MHz, OTHER DSP, PQFP44
文件頁數(shù)： 95/100頁
文件大小： 1547K
代理商： B900J24FXX12IT
B900
Advance Data Sheet
Baseband Signal Processor
July 1999
94
Lucent Technologies Inc.
9 Crystal Oscillator Electrical Requirements and Characteristics (continued)
9.2
Frequency Accuracy Considerations
For most applications, clock frequency errors in the hundreds of parts per million (ppm) can be tolerated with no
adverse effect. However, for applications where precise frequency tolerance on the order 100 ppm is required, care
must be taken in the choice of external components (crystal and capacitors) as well as in the layout of the printed-
circuit board. Several factors determine the frequency accuracy of a crystal-based oscillator circuit. Some of these
factors are determined by the properties of the crystal itself. Generally, a low-cost, standard crystal is not sufficient
for a high-accuracy application, and a custom crystal must be specified. Most crystal manufacturers provide exten-
sive information concerning the accuracy of their crystals, and an applications engineer from the crystal vendor
should be consulted prior to specifying a crystal for a given application.
In addition to absolute, temperature, and aging tolerances of a crystal, the operating frequency of a crystal is also
determined by the total load capacitance seen by the crystal. When ordering a crystal from a vendor, it is neces-
sary to specify a load capacitance at which crystal operating frequency is measured. Variations in this load capaci-
tance due to temperature and manufacturing variations cause variations in the operating frequency of the oscillator.
Figure 27 illustrates some of the sources of this variation.
CEXT = External load capacitor (one each required for XTALA and XTALB)
CD = Parasitic capacitance of the B900 itself
CB = Parasitic capacitance of the printed-wiring board
CO = Parasitic capacitance of crystal (not part of CL, but still a source of frequency variation)
CL = Calculated load capacitance to be provided to crystal vendor
5-4045.r3
Figure 27. Components of Load Capacitance for Crystal Oscillator
The load capacitance, CL, must be specified to the crystal vendor. The crystal manufacturer cuts the crystal so that
the frequency of oscillation is correct when the crystal sees this load capacitance. Note that C L refers to a capaci-
tance seen across the crystal leads, meaning that for the circuit shown in Figure 27, CL is the series combination of
the two external capacitors (CEXT/2) plus the equivalent board and device strays (CB/2 + CD/2). For example, if
10 pF external capacitors were used and parasitic capacitance is neglected, the crystal should be specified for a
load capacitance of 5 pF. If the load capacitance deviates from this value due to the tolerance on the external
capacitors or the presence of parasitic capacitance, the frequency also deviates. This change in frequency as a
function of load capacitance is known as pullability, which is expressed in units of ppm/pF.
CD
XTAL
XTAL1/2A
XTAL1/2B
CL
CB
CEXT
CD
CB
CEXT
CO
相關PDF資料
PDF描述
BA00CC0WCP-V5 1A Low Dropout Voltage Regulator with Shut Down Switch(Adustable Voltage)
BA10E6 COPPER ALLOY, TIN FINISH, RING TERMINAL
BA12004 0.5 A, 7 CHANNEL, NPN, Si, POWER TRANSISTOR
BA1518SUR5VP SINGLE COLOR DISPLAY CLUSTER, ULTRA RED
BA1524LUR5VP SINGLE COLOR DISPLAY CLUSTER, ULTRA RED
相關代理商/技術參數(shù)
參數(shù)描述
B-900-M-10 制造商:Thomas & Betts 功能描述:
B-900-M-10-EG 制造商:Thomas & Betts 功能描述:
B-900-M-20 制造商:Thomas & Betts 功能描述:
B-900-M-20-EG 制造商:Thomas & Betts 功能描述:
B901 制造商:EDAL 制造商全稱:EDAL 功能描述:Silicon Bridge Rectifier
發(fā)布緊急采購，3分鐘左右您將得到回復。

采購需求

(若只采購一條型號，填寫一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購。也可以進入我的后臺，查看報價

發(fā)布成功！您可以繼續(xù)發(fā)布采購。也可以進入我的后臺，查看報價

*型號 *數(shù)量 廠商 批號 封裝
添加更多采購

我的聯(lián)系方式

*
*
*