³⁷The circuit needed to compare $v_g$ and $v_{\mathit{𝑜𝑢𝑡}}$ is for example a differential pair. This circuit is used in most opamps that explicitly have a differential input, and is discussed in detail in chapter ??. For now, we assume an ideal subtraction point with an infinite input impedance and an output impedance of $0\mathrm{\Omega }$.