LTC1264 datasheet(13/30 Pages) LINER

13 / 30 page

LTC1068 Series

1068fc

MODES OF OPERATION

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 the parts nominal ratio. Figure 6

illustratesMode3,theclassicalstatevariableconfiguration,

providinghighpass,bandpassandlowpass2ndorderfilter

functions. Mode 3 is slower than Mode 1. Mode 3 can be

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

highpass filters.

PleaserefertotheOperatingLimitsparagraphunderApplica-

tions 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 the part’s nominal ratio.

The advantage of Mode 2 is that it provides less sensitivity

to resistor tolerances than does Mode 3. Mode 2 has a

highpassnotchoutputwherethenotchfrequencydepends

solely on the clock frequency and is therefore less than

the center frequency, fO.

PleaserefertotheOperatingLimitsparagraphunderApplica-

tions Information for a guide to the use of capacitor CC.

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

Bandpass and Lowpass Outputs

Figure 6. Mode 3, 2nd Order Section Providing

Highpass, Bandpass and Lowpass Outputs

Figure 7. Mode 2, 2nd Order Filter Providing Highpass

Notch, Bandpass and Lowpass Outputs

–

AGND

VIN

1068 F05

+ –

fO =

; fn = fO

Q =

; HON = –

; HOBP = –

HOLP = –

fCLK

RATIO

√ R6

(R6 + R5)

R6 + R5

√ R6

(R6 + R5)

( )

DEVICE

LTC1068

LTC1068-200

LTC1068-50

LTC1068-25

RATIO

100

200

–

AGND

VIN

1068 F06

+ –

1/4 LTC1068

fO =

fCLK

RATIO

√R2R4

(RATIO)(0.32)(R4)

(

)

1 –

(RATIO)(0.32)(R4)

(

)

1 –

( )

√R2R4

HOHP = –

; HOBP = –

; HOLP = –

; Q = 1.005

DEVICE

LTC1068

LTC1068-200

LTC1068-50

LTC1068-25

RATIO

100

200

–

AGND

HPN

VIN

1068 F07

+ –

fO =

; fn =

fCLK

RATIO

fCLK

RATIO

√ R2R4

1 +

Q = 1.005 R3

( )√ R2

1 +

(RATIO)(0.32)(R4)

(

)

1–

(RATIO)(0.32)(R4)

(

)

1–

HOHPN = –

(AC GAIN, f >> fO); HOHPN = –

1 +

( )

1 +

( )

(DC GAIN)

HOBP = – R3

; HOLP = –

DEVICE

LTC1068

LTC1068-200

LTC1068-50

LTC1068-25

RATIO

100

200

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