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发表于 2012-4-12 23:12:27
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>> 有什么办法让信号幅度不致衰减太多,改滤波器?要怎么改呢?
根据老外所述, 有四个0.1uF/0.047uF的交进连电容需要加大, 否则低频信号幅度衰减太多。两个位於AD9830A I 及 /I 输出至 LM6182 第一级输入, 一个位於 LM6182 输出至第二级放大输入, 及一个0.047uF位於第二级放大输出端。老外用 100uF 钽电容并连加大其电容侦值。你更应在 DDS 滤波电容上并连一个 1.5K 电阻, 否则 输出正弦波会失真。
Four coupling capacitors are used. Two 0.1uF (?) caps are between the AD9830A
I and /I outputs and the LM6182 first amplifier stage inputs. There is a 0.01
uF cap between the fist amplifier output and the second amplifier input and
there is a 0.047 uF cap on the second amplifier output. These four coupling
capacitors severely limit the lower frequency that the DDS board can operate
at. They can be paralleled by much higher values to decrease the minimum
frequency the board can operate at (I used 100uF tantalums). If you do this
you will also have to parallel one of the DDS filter caps with a resistor
(1.5K) to restore the sine wave output to its proper low distortion shape.
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