LTC1264 Datasheet, PDF(8/16 Page) Linear Technology – High Speed, Quad Universal Filter Building Block

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LTC1264 Datasheet, PDF (8/16 Pages) Linear Technology – High Speed, Quad Universal Filter Building Block

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LTC1264

ODES OF OPERATIO

VIN

AGND

Î£

â«

1/4 LTC1264

â«

1264 F07

â fi

fCLK

;

( ) â ( ) Q = 1.005

1 + R2

1â

6.42â¢R4

( ) HOHP

(AC

GAIN,

fn);

HOHPn

(DC GAIN, f < fn)

( ) HOBP

1â

6.42â¢R4

; HOLP = HOHPn

Figure 7. Mode 2, 2nd Order Filter Providing

Highpass Notch, Bandpass and Lowpass Outputs

Mode 3a

This is an extension of Mode 3 where the highpass and

lowpass output are summed through two external resis-

tors RH and RL to create a notch. This is shown in Figure

8. Mode 3a is more versatile than Mode 2 because the

notch frequency can be higher or lower than the center

frequency of the 2nd order section. The external op amp

of Figure 8 is not always required. When cascading the

sections of the LTC1264, the highpass and lowpass

outputs can be summed directly into the inverting input of

the next section.

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

the use of capacitor CC.

Mode 2n

This mode extends the circuit topology of Mode 3a to

Mode 2 (Figure 9) where the highpass notch and lowpass

outputs are summed through two external resistors RH

and RL to create a lowpass output with a notch higher in

frequency than the notch in Mode 2. This mode, shown in

Figure 8, is most useful in lowpass elliptic designs. When

cascading the sections of the LTC1264, the highpass

notch and lowpass outputs can be summed directly into

the inverting input of the next section.

Please refer to the Maximum Frequency of Operation

paragraph under Applications Information for a guide to

the use of capacitor CC.

VIN

AGND

Î£

â«

1/4 LTC1264

â â fi

fCLK

;

fn =

;

( ) â ( ) Q = 1.005 R3

1â

6.42â¢R4

( )( ) ( )( ) RG

HOHPn (f = â) =

; HOLPn (f = 0) =

HIGHPASS

OR LOWPASS

NOTCH OUTPUT

EXTERNAL OP AMP OR

INPUT OP AMP OF THE

LTC1264, SIDES A, B, C, D

1264 G08

Figure 8. Mode 3a, 2nd Order Filter Providing a Highpass Notch or Lowpass Notch Output

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