🔍 Key Concepts

• Review how an inverting op-amp is wired (which input is used, where the feedback resistor goes, and what that means for gain and phase). • Compare the labels and resistor values around U2 and U3 in figure A (note "Proportional gain amplifier" vs "Inverter"). • Recall the difference between a summing amplifier (multiple inputs into one node) and a simple gain stage (single input, single feedback resistor).

💭 Think About

• Look closely at U2’s input and feedback path: does it receive more than one signal, or just the error signal? What does that imply about summing vs simple amplification? • If U3 is already identified as an inverter, what function is left for U2 to perform in the proportional controller block? • How do the ratios of the resistors on U2 (input vs feedback) affect the magnitude and sign of the output relative to the error signal from U1?

✅ Before You Answer

• Confirm whether U2 has one or multiple input resistors tied to its summing junction (this tells you if it is a summing amplifier). • Check the feedback resistor ratio around U2 to determine if it provides a gain greater than 1 (|Vout| > |Vin|). • Verify from the drawing which stage specifically is labeled "Inverter" so you don’t assign the inverting function to the wrong op-amp.