LMV321-N, LMV321-N-Q1, LMV358-N, LMV358-N-Q1
LMV324-N, LMV324-N-Q1
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SNOS012I –AUGUST 2000–REVISED FEBRUARY 2013
From Equation 2 and Equation 9, we obtain
(10)
(11)
The values of C1 and C2 are normally close to or equal to
(12)
As a design example:
Require: ALP = 2, Q = 1, fc = 1 kHz
Start by selecting C1 and C2. Choose a standard value that is close to
(13)
(14)
From Equation 7 Equation 8 Equation 10 Equation 11,
R1= 1Ω
R2= 1Ω
R3= 4Ω
R4= 4Ω
(15)
(16)
(17)
(18)
The above resistor values are normalized values with ωn = 1 rad/s and C1 = C2 = Cn = 1F. To scale the
normalized cutoff frequency and resistances to the real values, two scaling factors are introduced, frequency
scaling factor (kf) and impedance scaling factor (km).
(19)
Scaled values:
R2 = R1 = 15.9 kΩ
R3 = R4 = 63.6 kΩ
C1 = C2 = 0.01 µF
(20)
(21)
(22)
An adjustment to the scaling may be made in order to have realistic values for resistors and capacitors. The
actual value used for each component is shown in the circuit.
2nd-Order High Pass Filter
A 2nd-order high pass filter can be built by simply interchanging those frequency selective components (R1, R2,
C1, C2) in the Sallen-Key 2nd-order active low pass filter. As shown in Figure 62, resistors become capacitors,
and capacitors become resistors. The resulted high pass filter has the same corner frequency and the same
maximum gain as the previous 2nd-order low pass filter if the same components are chosen.
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