LTC1067CS datasheet(10/20 Pages) AD

10 / 20 page

LTC1067/LTC1067-50

ODES OF OPERATIO

The parallel combination of R5 and R6 should be kept

below 5k.

Please refer to the Operating Limits paragraph under Appli-

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

Mode 3

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

center frequency of each 2nd order section can be ad-

justed above or below the part’s nominal ratio. Figure 5

illustrates Mode 3, the classical state variable configura-

tion, providing highpass, 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 highpass filters.

Please refer to the Operating Limits paragraph under Appli-

cations 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 6. 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

highpass-notch output where the notch frequency

depends solely on the clock frequency and is therefore

less than the center frequency, fO.

Please refer to the Operating Limits paragraph under Appli-

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

–

∫

AGND

VIN

1067 F05

–

fO =

fCLK

RATIO

HOHP = –

; HOBP = –

;

NOTE: RATIO = 100 FOR LTC1067

= 50 FOR LTC1067-50

HOLP = –

√R2

(RATIO)(0.32)(R4)

(

)

1 –

(RATIO)(0.32)(R4)

(

)

1 –

( )

√R2

; Q = 1.005

Figure 5. Mode 3, 2nd Order Section Providing

Highpass, Bandpass and Lowpass Outputs

Figure 6. Mode 2, 2nd Order Filter Providing Highpass

Notch, Bandpass and Lowpass Outputs

–

∫

AGND

VIN

1067 F04

–

fO =

; fn = fO

Q =

; HON = –

; HOBP = –

HOLP = –

fCLK

RATIO

√ R6

(R6 + R5)

R6 + R5

√ R6

(R6 + R5)

()

NOTE: RATIO = 100 FOR LTC1067

= 50 FOR LTC1067-50

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

Bandpass and Lowpass Outputs

–

Σ ∫

∫

AGND

HPN

VIN

1067 F06

–

fO =

; fn =

fCLK

RATIO

√ R2

1 +

fCLK

RATIO

Q = 1.005

( )√ R2

1 +

HOHPN = –

(AC GAIN, f >> fO); HOHPN = –

1 +

( ) (DCGAIN)

HOBP = –

; HOLP = –

NOTE: RATIO = 100 FOR LTC1067

= 50 FOR LTC1067-50

(RATIO)(0.32)(R4)

(

)

1 –

(RATIO)(0.32)(R4)

(

)

1 –

1 +

( )

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