AD831 Bias Current

Hi again,

I am having some problems adjusting the bias current of the AD831. According to the datasheet a resistor must be connected between the BIAS pin and Vp. And for minimum bias current, connect it directly without resistor.

The problem is that the BIAS pin is connected directly to Vn (confirmed with a multimeter). If a shortcircuit Vn to Vp... nothing good happens , and if I put a small resistor (100 ohm) the overall current is increased obviously (10V difference in a 100ohm resistor -> high current).

Anyone know how is the bias current generation implemented in the chip? (and why is shortcircuited to Vn?) Or any experience reducing the bias current?

Thanks.

Julio

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  • 0
    •  Analog Employees 
    on Mar 24, 2014 9:39 PM

    Hi Julio,

    I'm guessing you're running a dual supply, +/- 5V?

    1)  The LO input should be able to be biased to 0V when using dual supplies.  Have you tried driving it single ended like what is shown in Figure 9?

    2)  No you can DC couple the RF input, just make sure the common-mode is between -1V and +1V.

    3)  You should be able to leave the unused pins unconnected.

    Can you attach a schematic?  It would better help me understand exactly what you're doing.

    Thanks,

    Joel

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  • 0
    •  Analog Employees 
    on Mar 24, 2014 9:39 PM

    Hi Julio,

    I'm guessing you're running a dual supply, +/- 5V?

    1)  The LO input should be able to be biased to 0V when using dual supplies.  Have you tried driving it single ended like what is shown in Figure 9?

    2)  No you can DC couple the RF input, just make sure the common-mode is between -1V and +1V.

    3)  You should be able to leave the unused pins unconnected.

    Can you attach a schematic?  It would better help me understand exactly what you're doing.

    Thanks,

    Joel

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