LTC1164 데이터 시트보기 (PDF) - Linear Technology

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LTC1164

Low Power, Low Noise, Quad Universal Filter Building Block

Linear Technology 

LTC1164

APPLICATIO S I FOR ATIO

3. Offset Nulling

Lowpass filters may have too much DC offset for some

users. A servo circuit may be used to actively null the

offsets of the LTC1164 or any LTC switched capacitor

filter. The circuit shown in Figure 5 will null offsets to better

than 300µV. This circuit takes seconds to settle because of

the integrator pole frequency.

4. Noise

All the noise performance mentioned excludes the clock

feedthrough. Noise measurements will degrade if the

already described grounding, bypassing, and buffering

techniques are not practiced. The Wideband Noise vs Q

curve shown in the Typical Performance Characteristics

Section is a very good representation of the noise

performance of this device.

SEPARATE V+ POWER SUPPLY TRACE FOR BUFFER

R12

R11

VIN

R21

R22

LTC1164

R3

R32

V + TRACE FOR FILTER

POSITIVE

SUPPLY

7

0.1µF

1k

–

19

+

0.1µF

NEGATIVE

SUPPLY

1µF TA

4

7

1µF TA

0.1µF

0.1µF

LTC1164 • AI02

Figure 4. Buffering the Output of a 4th Order Bandpass Realization

FROM

FILTER

OUTPUT

TO FILTER

FIRST SUMMING

NODE

R3

100k

+

LT1012

–

R1

1M

C1

0.1µF

C2

R2

0.1µF

1M

C1 = C2 = LOW LEAKAGE FILM (I.E. POLYPROPYLENE)

R1 = R2 = METAL FILM 1%

LTC1164 • AI03

Figure 5. Servo Amplifier

U

ODES OF OPERATIO

PRIMARY MODES

Mode 1

In Mode 1, the ratio of the external clock frequency to the

center frequency of each 2nd order section is internally

fixed at 50:1 or 100:1. Figure 6 illustrates Mode 1 provid-

ing 2nd order notch, lowpass, and bandpass outputs.

Mode 1 can be used to make high order Butterworth

Iowpass filters; it can also be used to make low Q notches

and for cascading 2nd order bandpass functions tuned at

the same center frequency with unity gain. Mode 1 is faster

than Mode 3. Note that Mode 1 can only be implemented

with 3 of the 4 LTC1164 sections because section D has no

externally available summing node. Section D, however,

can be internally connected in Mode 1 upon special

request.

R1

VIN

R3

R2

–

+

N

S

+–

Σ∫

1/4 LTC1164

BP

LP

∫

AGND

fo

=

10f0C(L5K0);

fn

=

fO;

HOLP

=

–

R2

R1

;

HOBP

=

–

R3

R1

;

HON1

=

–

R2

R1

Q

=

R3

R2

LTC1164 • MOO01

Figure 6. Mode 1: 2nd Order Filter Providing Notch,

Bandpass, Lowpass

1164fa

9

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