OS(LP(N.INV ))

OS2

3

3

OS(LP(INV ))

OS1

OS2

2

2

V

V

R

R

V

V

1

V

R

R

=

æ

ö

=

+

-

ç

÷

è

ø

OS(HP)

OS2

3

3

3

OS(LP)

OS1

OS2

2

1

2

V

V

R

R

R

V

V

1

V

R

R

R

=

æ

ö

=

+

+

-

ç

÷

è

ø

OS(HP)

OS2

OS(BP)

OS3

OS(LP)

OS1

OS2

OS3

p

p

V

V

V

V

R4

R4

R4

V

V

1

V

V

R

R2

R3

R

R1|| R2 || R3

=

=

é

ù

æ

ö

æ

ö

=

+

-

-

ê

ú

ç

÷

ç

÷

è

ø

è

ø

ê

ú

ë

û

=

Not Recommended for New Designs

LMF100

www.ti.com

SNOSBG9B – JULY 1999 – REVISED JUNE 2015

Typical Application (continued)

Mode 3

Mode 6a and 6c

Mode 6b

Figure 59. Offset Voltage Sources

In many applications, the outputs are AC-coupled and DC offsets are not bothersome unless large signals are

applied to the filter input. However, larger offset voltages will cause clipping to occur at lower AC signal levels,

nominal value, especially if Q is also high.

For example, Figure 60 shows a second-order 60-Hz notch filter. This circuit yields a notch with about 40 dB of

attenuation at 60 Hz. A notch is formed by subtracting the bandpass output of a mode 3 configuration from the

input using the unused side B operational amplifier. The Q is 10 and the gain is 1 V/V in the passband. However,

R4/R2 = 100. The offset voltage at the lowpass output (LP) will be about 3 V. However, this is an extreme case

and the resistor ratio is usually much smaller. Where necessary, the offset voltage can be adjusted by using the

in modes 1a and 3, for example).

Copyright © 1999–2015, Texas Instruments Incorporated

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