How to set Gain in each stage while Cascading two ADA8282?


we are planning to use two ADA8282 in serial to achieve a gain of 54 dB in our acquisition hardware.we have some queries regarding the chipset.

1. we would like to know how to determine/choose gain of individual ADA8282 while cascading.  we thought we can set 24 dB in first stage and 30 dB in second stage as setting a lower gain in first stage will avoid saturation in second stage. But page 14 of the datasheet recommends 30 dB gain in stage 1 and 24 dB gain stage 2, we would like to know the benefits/reason of providing higher gain in stage1.

2. The page 12 of datasheet mentions output swing range as 6.3 vp-p. we would like to know the saturation limit of lna and vga, As per our calculation we are getting 316.931 vp-p as the maximum input voltage at lna without saturation and 1.5888 vp-p as the maximum input voltage  voltage at pga without saturation. are these values correct?

3.  is it  possible to realize a high pass filter inbetween the gain stages of ADA8282 while cascading two ADA8282?

  • 0
    •  Analog Employees 
    on Jun 18, 2020 1:50 PM 5 months ago

    Moved out of the RF & Microwave forum

  • 0
    •  Analog Employees 
    on Jul 9, 2020 4:40 PM 4 months ago

    Hi ppkarupan,

    Thank you for considering ADA8282 in your application.

    As for your query, we usually set/take as much gain as early possible in the signal chain to reduce the contribution of the noise sources after the gain stage. As a result the signal is stronger relative to the noise. But if you noticed for the case of gain of 42dB on table 11 (with gain of 18dB as the first stage and gain of 24dB on second stage) this allows the maximum output swing on the second stage since it's indicated on table 8 that at 18dB gain configuration only 3.1Vpp output swing is allowed.

    As for the output swing range it's indicated that at a gain of 18dB, it only allows up to 3.1Vpp and the with higher gain allows 6.3Vpp. This means that you have to adjust your input range according to the gain to avoid saturating the device.

    Hope this helps ppkarupan.
    Apologies for the delayed response.

    Best Regards,