- #1
Jason-Li
- 119
- 14
- Homework Statement
- FIGURE 2 shows an electronic 'black box' whose output is ten times the difference between its two input signals. Show how the 'black box' could be realised using just two operational amplifiers and five resistors. Give the relative values of the resistors.
(Figure 2 Attached in attempt)
- Relevant Equations
- Below example of Op Amp controller (Figure 9)
So basically I am trying to give an output of Vo = 10(V2-V1)
From Figure 9 Example Gain of first Op Amp = Rf / R1, if R1 & R2 are equal.
What's throwing me off is using 5 resistors to create a circuit rather than 6 or just 3. My initial thoughts were the following:
To use the first loop simply to give a straight comparitive figure between V1 & V2 or (V2-V1) then use the second loop to mulitply that comparitive figure by 10. No bias would be introduced so the circuit would be akin to Figure 9 but with no bias voltage. The circuit would look like the following with R3=1ohm and R4=10ohm which would make the second loop gain 10/1.
I just don't see why I need the second loop or 5 resistors when this could be acheived with just the first loop to function as a comparator and prop. amplifier. Such that the first loop R1=R2=2Mohms and Rf = 20Mohms hence Vo=Rf/R1(V2-V1) will be equal to Vo=10(V2-V1)
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