Determine if feedback is negative or positive?

Is there a way to know from how a circuit is designed that is has negative feedback or positive feedback. Here are some examples:

Example 1:

Example 2:

• Yes there is, select a loop, pick any point in that loop. Now imagine that there is a positive disturbance (increasing voltage or current) on that node and how it flows through the loop. If it ends up at the starting point also with a positive disturbance so adding to the disturbance you started with: it is positive feedback. If the disturbance counteracts (works against) the disturbance you started with, it is negative feedback. – Bimpelrekkie Oct 26 '17 at 13:52
• Thanks for the response. I don't understand all that much...is it possible show what you are saying because I am not seeing it clearly. – user4826575 Oct 26 '17 at 13:55
• For the first circuit: where is the loop? It is gate of NMOS => drain of NMOS => 1 Meg resistor => back at gate. Now imagine the voltage at the gate increases a little bit, that means that the NMOS would start to conduct a bit more as Vgs becomes larger. That means the NMOS makes a bit more drain current flow. That means the drain voltage goes down a bit (more voltage drops across the drain resistor). So the voltage at the right side of the 1 M ohm resistor is pulled down a bit, this will also pull down the voltage on the left side, which is was our starting point. – Bimpelrekkie Oct 26 '17 at 14:03
• So an increase in voltage (at the gate) results in a decrease of the voltage on the same node through the feedback. So this means it is .... feedback (for you to answer). – Bimpelrekkie Oct 26 '17 at 14:04
• allaboutcircuits.com/textbook/semiconductors/chpt-4/feedback ;-) hope this solves your troubles. – Mitu Raj Oct 26 '17 at 14:06