OP179/OP279

–14–

REV. F

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 capaci-

tors. In configuring the circuit for other frequencies, comple-

mentary 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 sug-

gested 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 SK stage U1A: R1 = R2, and C1 = C2, etc.

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