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Inverting realization of 7(s+400)/(s+200)

Short answer

Inverting configuration with parallel RC at input and feedback: choose C2=0.1 μF, then C1=0.7 μF, R1=1/(400×0.7 μF)≈3.57 kΩ, R2=1/(200×0.1 μF)=50 kΩ. Realizes −7(s+400)/(s+200); add unity‑gain inverter if sign inversion is undesired.

Design the following transfer function using inverting op-amp configuration. T(s) = 7(s+400)/(s+200). You are not allowed to use inductors in the design.

Given T(s)=7s+400s+200T(s) = 7\dfrac{s+400}{s+200}: HF gain 7, DC gain 14, zero at −400, pole at −200. Only R, C and op-amps are used (no inductors).

Inverting configuration: Z1Z_1 from the input to the inverting input, Z2Z_2 in feedback:

T(s)=−Z2Z1=−Y1Y2T(s) = -\frac{Z_2}{Z_1} = -\frac{Y_1}{Y_2}

With Y1=1R1+sC1Y_1 = \dfrac{1}{R_1} + sC_1 (parallel R1C1R_1C_1) and Y2=1R2+sC2Y_2 = \dfrac{1}{R_2} + sC_2 (parallel R2C2R_2C_2):

T(s)=−C1C2⋅s+1R1C1s+1R2C2T(s) = -\frac{C_1}{C_2}\cdot\frac{s + \frac{1}{R_1C_1}}{s + \frac{1}{R_2C_2}}
              +---R2---+
              |        |
              +---||---+
       R1     |   C2   |
  +--/\/\--+  |        |
Vin        +--+-|-\    |
  +---||---+    |  >---+--- Vo
       C1   GND-|+/

Matching:

C1C2=71R1C1=4001R2C2=200\begin{aligned} \frac{C_1}{C_2} &= 7 \\ \frac{1}{R_1C_1} &= 400 \\ \frac{1}{R_2C_2} &= 200 \end{aligned}

Choose C2=0.1 μC_2 = 0.1\ \muF, so C1=0.7 μC_1 = 0.7\ \muF:

R1=1400×0.7×10−6=3.571 kΩR2=1200×0.1×10−6=50 kΩ\begin{aligned} R_1 &= \frac{1}{400 \times 0.7\times10^{-6}} = 3.571\ \text{k}\Omega \\ R_2 &= \frac{1}{200 \times 0.1\times10^{-6}} = 50\ \text{k}\Omega \end{aligned}

Check: DC gain =R2/R1=50/3.571=14=7×400/200= R_2/R_1 = 50/3.571 = 14 = 7 \times 400/200. Correct.

ElementValue
R1R_13.57 kΩ
C1C_10.7 μF
R2R_250 kΩ
C2C_20.1 μF

Answer: R1=3.57 kΩ∥C1=0.7 μR_1 = 3.57\ \text{k}\Omega \parallel C_1 = 0.7\ \muF at the input, R2=50 kΩ∥C2=0.1 μR_2 = 50\ \text{k}\Omega \parallel C_2 = 0.1\ \muF in feedback. The circuit gives −7(s+400)/(s+200)-7(s+400)/(s+200); add a unity-gain inverting amplifier (two equal resistors) if the positive sign is required.

✓ Answer checked by Claude Sonnet 5.5

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