An Op-amp based circuit is shown in figure below. Current I0 is
1
\(\frac{\text{V}_{\text{s}}}{\text{R}_{\text{L}}}\)
2
\(\frac{\text{V}_{\text{s}}}{\text{R}_{\text{s}}}\)
3
\(\text{V}_{\text{S}} \times \frac{\text{R}_{\text{L}}}{\text{R}_{\text{s}}\left(\text{R}_{\text{L}}+\text{R}_{\text{s}}\right)}\)
4
\(\text{V}_{\text{s}}\left(\frac{1}{R_{\text{s}}}+\frac{1}{R_{L}}\right)\)