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Can anyone help me identify where the negative feedback path is? I want to determine the feedback factors for both negative and positive feedback. However, it's not clear to me where the negative feedback loop is.

enter image description here

The image is from this paper.

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    \$\begingroup\$ @MrGerber but my question is about the loop, what is the path or loop instead of a point. \$\endgroup\$
    – hana
    Commented Jul 10 at 12:51

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Suppose the comparator front end is at balance. You can simplify it as the drains both being connected to fixed voltages and the sources connected together to a current sink. At balance each transistor is conducting half the constant current \$I_0\$.

As V1 (gate voltage of M1) increase the proportion of current passing through M1 increases so the source voltage Vs will increase, which reduces the Vgs increase M1 sees.

At the balance point, the negative feedback is 50% (a 1uV change at the gate results in a 500nV change in Vgs).

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  • \$\begingroup\$ Hi, thanks for the answer. If we consier only half-circuit (M1, M3, M5), would there still exist negative feedback? It is a source follower to me and I don't see there is a negative feedback in it. For example, if V1 increases, then Vs increases at the same rate to make the tail current constant. \$\endgroup\$
    – hana
    Commented 12 hours ago

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