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发表于 2007-12-13 16:36:00
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<DIV class=quote><B>以下是引用<I>googoo</I>在2006-8-30 22:21:00的发言：</B>
系列二 10. Two equal amplitude tones have a power of +10 dBm, and generate a pair of equal amplitude 3rd-order intermodulation products at -20 dBm. What is the 2-tone, 3rd-order intercept point (IP3) of the system?
b) +25 dBm
2-tone, 3rd-order intermod products increase 3 dB in power for every 1 dB increase in tones that produce them. That means the intermods increase in power at a rate of 2 dB per 1 dB relative to the tone power. The 2-tone, 3rd-order intercept point is defined as the theoretical point where the two original tones and the two 3-rd-order products would have equal power (not possible in real systems due to saturation limits).
If the two original tones have a power of +10 dBm and the 3rd-order products have a power of -20 dBm, then the intercept point will be at +10 dBm + [(+10) - (-20)]/2 dB = +10 dBm + 15 dB = +25 dBm.
好像题目不清楚哦，
按这个解释，默认了系统增益为0dB
否则应该是25+0.5*Gain[/COLOR]</DIV>
三阶截至点定义为基频输出分量等于三阶交调输出分量的那个点的输出功率值，这是理论上的点。这里计算的时候与增益无关。原因如下：
在对数为单位的坐标系，横坐标是输入功率，纵坐标是输出功率，基频的变化曲线斜率是1，增益只影响这个曲线在x=0时的y值（P1out=Pin+G1）；三阶交调频率的变化曲线斜率是3 （P3out=3*Pin+G2）。
现在P1out=10dBm，P3out=-20dBm。相差30dBm，那么什么时候相等呢？
Pin每增加1dB，P1out也增加1dB，但是P3out增加3dB，两者增长相差2dB。
相等的时候,P1out=10+30/2=P3out=-20+(30/2)*3=25[br]<p align=right><font color=red>+3 RD币</font></p> |
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