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AD9956的DAC输出及双端转单端电路

woshi2 在 2014-6-5 詢問的問題
最後回覆由ADI_Wei於2014-6-13提供

1.AD9956的DAC输出是电流型的,根据datasheet中说明,是指IOUT+只在正弦波正半周输出电流有输出,而负半周无电流,电阻上无压降,从而该管脚电平为1.8V;IOUT- 则相反。是这样理解吗?

     可实际我测试发现,单独测量IOUT+/-都是完整的正弦波波形,且为1.53±0.27sinwt,偏置电压为1.53V。

Finally, the amplitude words are piped to a 14-bit DAC. Because the DAC is a sampled data system, the output is a reconstructed sine wave that needs to be filtered to take high frequency images out of the spectrum. The DAC is a current-steering DAC that is AVDD referenced. To get a measurable voltage output, the DAC outputs must terminate through a load resistor to AVDD, typically 50 Ω. At positive full scale, IOUT sinks no current and the voltage drop across the load resistor is zero. However, the IOUT output sinks the DAC’s programmed full-scale output current, causing the maximum output voltage to drop across the load resistor. At negative full-scale, the situation is reversed and IOUT sinks the full-scale current (and generates the maximum drop across the load resistor). At the same time, IOUT sinks no current (and generates no voltage drop). At midscale, the outputs sink equal amounts of current, generating equal voltage drops.

 

2.如1中所说,正弦波幅值为0.27V,差分后,为0.54V,看datasheet上没有说明如何控制DAC输出的电流幅值,只知道DAC_RSET接的电阻和它有关,具体关系是什么呢?

3.由于我们使用的场合是低频(输出50 kHz左右,REF_CLK 为10 MHz),所以使用变压器就不太合适了。尝试过仪表放大器,但是由于系统单电源供电,共模和差模输入范围不合适,最后看到了AD8130这个差分放大器,专门用于将互补DAC输出转为单端信号的。

     可实际使用发现所有输入和供电都符合要求,AD8130的输出却为0.9+0.1sinwt类似的波形(噪声非常明显),不知道您知道是怎么回事吗?换了个芯片还是一样。

     AD8130连接如下:+Vs +5V; -Vs 0V; REF 2.5V;PD +5V; FB和OUT短接;IN+/- 分别接 AD9956的IOUT+/-(都接了50R电阻到AVDD,也就是1.8V上,电压测量为1.53±0.27sinwt).

 

希望大家帮忙解答,谢谢

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