Datasheet
LTC1064
8
1064fb
–
+
∫ ∫
LP
1064 F05
+
Σ
AGND
1/4 LTC1064
NS
–
R1
R2
V
IN
R3
f
O
= ; f
n
= f
O
; H
OLP
= – ; H
OBP
= – ; H
ON1
= – ; Q =
f
CLK
100(50)
R2
R1
R3
R1
R3
R2
R2
R1
BP
C2
0.1µF
C1
0.1µF
R1
1M
R2
1M
1064 F04
TO FILTER
FIRST SUMMING
NODE
C1 = C2 = LOW LEAKAGE FILM
(I.E., POLYPROPYLENE)
R1 = R2 = METAL FILM 1%
FROM
FILTER OUTPUT
R3
100k
–
+
LT1012
7
19
R21
R11
R31
4
7
LTC1064
0.1µF
1µF
V
OUT
1064 F03
10k
R32
R22
R12
0.1µF
V
+
TRACE FOR FILTER
0.1µF
V
IN
–
+
10k
LT
®
318
LT1007
LT1056
NEGATIVE
SUPPLY
POSITIVE
SUPPLY
SEPARATE V
+
POWER SUPPLY TRACE FOR BUFFER
1µF
0.1µF
+
+
APPLICATIONS INFORMATION
WUU
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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 LTC1064 or any LTC switched-capacitor
filter. The circuit shown in Figure 4 will null offsets to better
than 300µV. This circuit takes seconds to settle because of
the integrator pole frequency.
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 graph Wideband Noise
vs Q in the Typical Performance Characteristics section is
a very good representation of the noise performance of
this device.
Figure 3. Buffering the Output of a 4th Order Bandpass Realization
Figure 4. Servo Amplifier
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 5 illustrates Mode 1 provid-
ing 2nd order notch, lowpass and bandpass outputs.
Mode 1 can be used to make high order Butterworth
lowpass 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 three of the four LTC1064 sections because Section
D has no externally available summing node. Section D,
however, can be internally connected in Mode 1 upon
special request.
ODES OF OPERATIO
U
W
Figure 5. Mode 1: 2nd Order Filter Providing Notch,
Bandpass and Lowpass