LTC1264 Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LTC1264

High Speed, Quad Universal Filter Building Block

Linear Technology 

W

U

ODES OF OPERATIO

optimum mode for high Q designs with fCLK to fCUTOFF (or

fCENTER) ratios greater than 20:1.

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

the use of capacitor CC.

R1

VIN

R3

R2

–

+

AGND

CC

N

S

BP

LP

+

–

Σ

∫

∫

1/4 LTC1264

1264 F04

fi

=

fCLK

20

;

fO

=

fi;

fn

=

fO

Q

=

R3

R2

;

HON

=

–

R2

R1

;

HOBP

=

–

R3

R1

HOLP = HON

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

Bandpass and Lowpass Outputs

R1

VIN

CC

R6

R5

R3

R2

N

S

BP

LP

–

+

AGND

+

–

Σ

∫

∫

1/4 LTC1264

1264 F05

NOTE: R5 ≤ 5k

√ fi

=

fCLK

20

;

fO

=

fi

R6

(R6 + R5)

;

fn

=

fO

√ Q = R3

R2

(R6R+6R5);

HON

=

–

RR21;

HOBP

=

–

R3

R1

( ) HOLP

=

–

R2

R1

R6 + R5

R6

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

Bandpass and Lowpass Outputs

LTC1264

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

the use of capacitor CC.

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,

fCLK/fO, is always less than 20:1. The advantage of Mode

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-

quency, fO.

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

the use of capacitor CC.

CC

R4

R3

R1

VIN

AGND

R2

HP

S

BP

LP

–

+

–

Σ

∫

∫

+

1/4 LTC1264

1264 F06

√ ( )√ ( ) fi =

fCLK

20

;

fO = fi

R2

R4

;Q

=

1.005

R3

R2

R2

R4

1

1

–

R3

6.42•R4

( ) HOHP

=

–

RR21;

HOBP

=

–

R3

R1

1

1

–

R3

6.42•R4

;

HOLP

=

–

R4

R1

Figure 6. Mode 3, 2nd Order Section Providing

Highpass, Bandpass and Lowpass Outputs

1264fb

7

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