将AD768电流放大后的电压输出无变化

我按照数据手册中的下图连接方式将AD768的输出电流转换成电压值。

放大器用的是AD811,Rfb用的是120R。时钟信号的输入是晶振产生的27M的正弦波。

其他的连接全部是按数据手册中来的。参考电压用的是内部2.5V参考电压,参考电压的输出是正确的。

16个数据位的输入无论是固定在0还是65535,还是别的其他值,放大器的输出都是-2.4V左右,不会有改变。

问:可能是哪些原因造成的这种错误呢?是晶振?还是对AD768的操作有错误?

请帮忙解答一下,谢谢

  • 0
    •  Analog Employees 
    on Jun 26, 2017 6:46 AM

    检查一下电平是否正确, 时序是否符合要求,

    此外输出的50欧姆电阻是否 安装了

  • AD768属于Not recommend的旧型号了的,我们手头资料也很少

    1)电源用的是+/-5V?

    2)晶振是有源还是无源的?直接接到Clock管脚,还是经过施密特触发器整形再接入?

    Datasheet P8/20

    DIGITAL INPUTS

    The clock can be operated at any dutycycle that meets the specified minimum latch pulse width. The setup and hold times can also be varied within the clock cycle as long as the specified minimums are met, although the location of these transition edges may affect digital feedthrough. The digital inputs are CMOS compatible with logic thresholds set to approximately half the positive supply voltage. The small input current requirements allow for easy interfacing to unbuffered CMOS logic. Figure 11 shows the equivalent digital input circuit.

    再看datasheet P16/20

    Clock Input
    An external sample clock must be provided to either the BNC connector labeled “CLOCK” or on Pin 33 of the IDC connector. This clock must comply with the logic levels outlined in the AD768 data sheet. The “CLOCK” input is terminated with a removable 51 resistor. The IDC connector clock connection is unterminated.

    具体的接法见Figure 35左下脚J1。

    也就是说,Clock Input也得符合datasheet P2/20  DIGITAL INPUTS的电平及时序要求的

    以上供您参考。