7

LTC1264

ODES OF OPERATIO

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

–

+

Σ

∫

∫

AGND

R1

N

BP

LP

1264 F04

+

–

S

1/4 LTC1264

R2

R3

Q =

R2

R1

R3

R1

R3

R2

20

Figure 4. Mode 1, 2nd Order Filter Providing Notch,

Bandpass and Lowpass Outputs

–

+

Σ

∫

∫

AGND

R1

N

BP

LP

1264 F05

+

–

S

NOTE: R5

≤ 5k

R2

R3

R5

R6

Q =

R2

R1

R3

R1

R3

R2

20

(R6 + R5)

R2

R1

R6 + R5

R6

1/4 LTC1264

(R6 + R5)

()

Figure 5. Mode 1b, 2nd Order Filter Providing Notch,

Bandpass and Lowpass Outputs

Mode 3

In Mode 3, the ratio of the external clock frequency to the

center frequency of each 2nd order section can be

adjusted above or below 20:1. Figure 6 illustrates Mode 3,

the classical state variable configuration, providing high-

pass, bandpass, and lowpass 2nd order filter functions.

Mode 3 is slower than Mode 1. Mode 3 can be used to

make high order all-pole bandpass, lowpass, and high-

pass filters.

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

Mode 2

Mode 2 is a combination of Mode 1 and Mode 3, shown in

Figure 7. With Mode 2, the clock-to-center frequency ratio,

2 is that it provides less sensitivity to resistor tolerances

than does Mode 3. As in Mode 1, Mode 2 has a notch

output which depends on the clock frequency, and the

notch frequency is therefore less than the center fre-

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

–

+

Σ

∫

∫

AGND

R1

HP

BP

LP

1264 F06

+

–

S

1/4 LTC1264

R2

R3

R4

; Q = 1.005

20

R3

R2

R4

R3

6.42•R4

(

)

1

1 –

( )

R4

;

R2

R1

R3

R1

R3

6.42•R4

(

)

1

1 –

R4

R1

Figure 6. Mode 3, 2nd Order Section Providing

Highpass, Bandpass and Lowpass Outputs