OP179/OP279

–14–

REV. G

References on Active Filters and Active Crossover Networks

1. Sallen, R.P.; Key, E.L., “A Practical Method of Designing

RC Active Filters,” IRE Transactions on Circuit Theory, Vol.

CT-2, March 1955.

2. Huelsman, L.P.; Allen, P.E., Introduction to the Theory and

Design of Active Filters, McGraw-Hill, 1980.

3. Zumbahlen, H., “Chapter 6: Passive and Active Analog

Filtering,” within 1992 Analog Devices Amplifier Applications

Guide.

4. Zumbahlen, H., “Speaker Crossovers,” within Chapter 8 of

1993 Analog Devices System Applications Guide.

5. Linkwitz, S., “Active Crossover Networks for Noncoincident

Drivers,” JAES, Vol. 24, #1, Jan/Feb 1976.

The crossover example frequency of 500 Hz can be shifted lower

or higher by frequency scaling of either resistors or capacitors. In

configuring the circuit for other frequencies, complementary LP/

HP action must be maintained between sections, and component

values within the sections must be in the same ratio. Table II

provides a design aid to adaptation, with suggested standard

component values for other frequencies.

Table II. RC Component Selection for Various Crossover

Frequencies

R1/C1 (U1A)

*

Crossover Frequency (Hz)

R5/C3 (U1B)

**

100

160 k

Ω/0.01 µF

200

80.6 k

Ω/0.01 µF

319

49.9 k

Ω/0.01 µF

500

31.6 k

Ω/0.01 µF

1 k

16 k

Ω/0.01 µF

2 k

8.06 k

Ω/0.01 µF

5 k

3.16 k

Ω/0.01 µF

10 k

1.6 k

Ω/0.01 µF

Table notes (applicable for

α = 2).

** For MFB stage U1B: R6 = R5, R7 = R5/2, and C4 = 2C3.