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Non-inverting: zero at -4, pole at -8, HF gain 2

Short answer

T(s)=2(s+4)/(s+8). Using non-inverting topology with series RC (R1, C1) to ground and feedback R2: R1=R2=12.5 kΩ, C1=10 μF; HF gain2, zero at −4, pole at −8.

Realize an active filter using non-inverting op-amp configuration with a zero at s = -4 and a pole at s = -8 having high frequency gain of k = 2.

Required function: zero at s=−4s=-4, pole at s=−8s=-8, HF gain 2:

T(s)=2 s+4s+8T(s) = 2\,\frac{s+4}{s+8}

DC gain =2×4/8=1= 2 \times 4/8 = 1. The zero is closer to the origin than the pole (a lead-type network): the gain rises from 1 at DC to 2 at high frequency, with phase lead in between.

Non-inverting configuration: Z1Z_1 from the inverting input to ground, Z2Z_2 from output to inverting input:

T(s)=1+Z2Z1T(s) = 1 + \frac{Z_2}{Z_1}

Use Z2=R2Z_2 = R_2 and Z1=R1+1sC1Z_1 = R_1 + \dfrac{1}{sC_1} (series RC to ground):

T(s)=1+sR2C11+sR1C1=1+s(R1+R2)C11+sR1C1=R1+R2R1⋅s+1(R1+R2)C1s+1R1C1\begin{aligned} T(s) &= 1 + \frac{sR_2C_1}{1 + sR_1C_1} = \frac{1 + s(R_1+R_2)C_1}{1 + sR_1C_1} \\ &= \frac{R_1 + R_2}{R_1}\cdot\frac{s + \frac{1}{(R_1+R_2)C_1}}{s + \frac{1}{R_1C_1}} \end{aligned}
              +---R2---+
              |        |
   +----------+-|-\    |
   |            |  >---+--- Vo
  R1    Vin-----|+/
   |
  === C1
   |
  GND

Matching:

1R1C1=81(R1+R2)C1=4⇒R1+R2=2R1⇒R2=R1HF gain=R1+R2R1=2  (satisfied)\begin{aligned} \frac{1}{R_1C_1} &= 8 \\ \frac{1}{(R_1 + R_2)C_1} &= 4 \Rightarrow R_1 + R_2 = 2R_1 \Rightarrow R_2 = R_1 \\ \text{HF gain} &= \frac{R_1+R_2}{R_1} = 2 \;(\text{satisfied}) \end{aligned}

Normalized (C1=1C_1 = 1 F): R1=R2=0.125 ΩR_1 = R_2 = 0.125\ \Omega.

Practical values: choose C1=10 μC_1 = 10\ \muF: R1=18×10−5=12.5 kΩR_1 = \dfrac{1}{8 \times 10^{-5}} = 12.5\ \text{k}\Omega, R2=12.5 kΩR_2 = 12.5\ \text{k}\Omega.

Answer: R1=R2=12.5 kΩR_1 = R_2 = 12.5\ \text{k}\Omega, C1=10 μC_1 = 10\ \muF; T(s)=2(s+4)/(s+8)T(s) = 2(s+4)/(s+8).

✓ Answer checked by Claude Sonnet 5.5

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