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Transform given low pass ladder to 2 kHz high pass

Short answer

LP to HP transformation substitutes s→ωp/s with ωp=2π×2000≈12566 rad/s. Series inductor L becomes series capacitor C=1/(Lωp): 3 H → 26.53 µF, 1 H → 79.58 µF. Shunt capacitor becomes shunt inductor L=1/(Cωp): 2/3 F → 119.4 µH. Load 2 Ω unchanged.

The following low pass filter has passband frequency ωp of 1 rad/s. Transform it into a highpass filter having passband frequency of 2KHz. [Figure: source Vs, series 3 H inductor, shunt 2/3 F capacitor, series 1 H inductor, 2 Ω load resistor]

For LP → HP we substitute s→ωp/ss \to \omega_p/s. Then a series inductor LL (impedance sLsL) becomes ωpL/s\omega_p L/s, i.e. a series capacitor, and a shunt capacitor becomes a shunt inductor. Resistors are unchanged.

Cnew=1L ωp,Lnew=1C ωpC_{new} = \frac{1}{L\,\omega_p}, \qquad L_{new} = \frac{1}{C\,\omega_p}

Given: prototype ωp=1\omega_p = 1 rad/s with series L1=3L_1 = 3 H, shunt C2=2/3C_2 = 2/3 F, series L3=1L_3 = 1 H, RL=2 ΩR_L = 2\ \Omega. New passband edge fp=2f_p = 2 kHz:

ωp=2π×2000=12566.37 rad/s\omega_p = 2\pi\times2000 = 12566.37\ \text{rad/s}

Element values

C1=13×12566.37=26.53 μFL2=1(2/3)×12566.37=119.37 μHC3=11×12566.37=79.58 μFRL=2 Ω (unchanged)\begin{aligned} C_1 &= \frac{1}{3\times12566.37} = 26.53\ \mu\text{F} \\ L_2 &= \frac{1}{(2/3)\times12566.37} = 119.37\ \mu\text{H} \\ C_3 &= \frac{1}{1\times12566.37} = 79.58\ \mu\text{F} \\ R_L &= 2\ \Omega\ \text{(unchanged)} \end{aligned}
LP elementHP elementValue
series L1=3L_1 = 3 Hseries C1C_126.53 µF
shunt C2=2/3C_2 = 2/3 Fshunt L2L_2119.37 µH
series L3=1L_3 = 1 Hseries C3C_379.58 µF
RL=2 ΩR_L = 2\ \OmegaRLR_L2 Ω
o-(Vs)-[C1]-+-[C3]-+
            |      |
          [L2]   [RL]
            |      |
o-----------+------+

Answer: C1=26.53 μC_1 = 26.53\ \muF, L2=119.37 μL_2 = 119.37\ \muH, C3=79.58 μC_3 = 79.58\ \muF, RL=2 ΩR_L = 2\ \Omega; the circuit passes frequencies above 2 kHz. (These values can be impedance scaled later if a larger load resistance is needed.)

✓ Answer checked by Claude Sonnet 5.5

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