Let $A,B$ be $k$-linear (possibly, dg-)categories, let $f,g:A\to B$ be two linear functors, and let $T:f\Rightarrow g$ be a natural isomorphism.
If one denotes by $C_\bullet(A,A)$ the standard Hochschild chain complex of $A$ with coefficients in itself, then $f$ and $g$ induce two chain maps $\mathbf{f},\mathbf{g}:C_\bullet(A,A)\to C_\bullet(B,B)$.
One knows from general facts about the homotopy theory of dg-categories that there exists a homotopy $\mathbf{T}$ between $\mathbf{f}$ and $\mathbf{g}$.
Here is my question: Is there a reference where one can find an explicit expression for this homotopy?
Ideally, I'd like a reference where the compatibility with the mixed structure on Hochschild chains (that is, with Connes' boundary operator) is discussed.
One can of course guess (and, with some work, prove) a formula. I'm almost sure such a formula is already written somewhere, but I couldn't find a reference.
Note that I'd already be happy to know about a reference for (dg-)algebras (in which case a natural isomorphism $T:f\Rightarrow g$ is just the data of an invertible element $b$ of $B$ such that for every $a\in A$, $bf(a)=g(a)b$).
