2020 Solution 03

Consider the two circuits below.
The equations show that the resistor ladder abstraction in (a) and the opamp amplifier in (b) are equivalent. Therefore, locate the negative resistor in (b).​
​(a) R1​
​(b) R2​
​(c) R3​
​(d) R1//R2​
​(e) There is none.
The mechanism of operation in circuit in (b) does not involve creating negative resistors. The opamp effects amplification by causing the voltage at the lower end of R2 (net-out) to "drop off" by a large amount w.r.t the virtual ground net at the negative input (-) of the opamp.
◼
  • There is no network path in (b) where the current flows opposite to the applied voltage.
    • Models may not always capture the underlying mechanism responsible for a particular circuit behavior.