AD8310;AD8338;gain control

Hi,

I used AD8310 as a detector, and converted the detected voltage to the desired voltage range through the invert phase scale converter circuit. However, when I connected the output of the detector to the invert phase scale converter circuit, undesirable results would appear (As shown in Figure 1 and 2).When inserting the voltage follower between them, I can get the result I want (As shown in Figure 3 and 4). However, after the simulation, I find that the output of the invert scale converter circuit is different from what I want. What should I do?The next level is AD8338, and the circuit is shown in Figure 5.

FIG. 1

FIG. 3

FIG. 4

FIG. 5



supplement
[edited by: rookie1 at 1:57 PM (GMT -5) on 29 Dec 2020]
Parents
  • +1
    •  Analog Employees 
    on Jan 7, 2021 12:50 AM

    Hi there,

    looking at the schematics above, the signals appear very low frequency, or DC. Because of that, we might ignore the effect of C6 (or C15), the 1uF capacitor for the moment.

    The op amp DC gain of the first circuit above is -50.54 / (10,000 + 100).

    The op amp DC gain of the second circuit above is -50.54 / 100.

    These are very different gains. Perhaps this could be the root cause of the issue.

    Both of these estimates neglect the 0.05 Ohms small signal output impedance of AD8310.

Reply
  • +1
    •  Analog Employees 
    on Jan 7, 2021 12:50 AM

    Hi there,

    looking at the schematics above, the signals appear very low frequency, or DC. Because of that, we might ignore the effect of C6 (or C15), the 1uF capacitor for the moment.

    The op amp DC gain of the first circuit above is -50.54 / (10,000 + 100).

    The op amp DC gain of the second circuit above is -50.54 / 100.

    These are very different gains. Perhaps this could be the root cause of the issue.

    Both of these estimates neglect the 0.05 Ohms small signal output impedance of AD8310.

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