# Question about feedback in a current reference

I'm studying the following Vbe-based current reference: The author of my book says:

Observe that the circuit has two feedback paths around the gain stage. One positive, the other negative. Assuming transistors M1 and M2 matched, equal currents are injected into R and into the diode connected transistor Q1. The voltage across a diode changes as the logarithm of the current; therefore, the feedback on the resistor side is typically stronger than the one on the bipolar transistor side. Transistor M2 and resistance R form an inverting amplifier. Therefore, in order to ensure stability, node B must be connected to the positive terminal of the differential gain stage.

I've understood that the loop which contains M2 is the negative feedback loop and the loop which contains M1 is the positive feedback loop (to check it, it is sufficient to break the wire, apply a small voltage increase and note that M1 and M2 are common-source configurations, which thus invert the signal). But what does it mean, from a mathematical/electrical point of view, that "the feedback on the resistor side is typically stronger than the one on the bipolar transistor side"? What would happen, from a stability point of view, if inverting and non-inverting terminals of the op-amp would be exchanged? How to work in general when we have two (or more) feedback loops?

• how will you start up this circuit? – analogsystemsrf Aug 29 '19 at 3:29