Datasheet
LTC1164
9
1164fa
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.
Figure 4. Buffering the Output of a 4th Order Bandpass Realization
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.
Figure 5. 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 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.
Figure 6. Mode 1: 2nd Order Filter Providing Notch,
Bandpass, Lowpass
APPLICATIO S I FOR ATIO
WUUU
LTC1164 • AI03
R3
100k
TO FILTER
FIRST SUMMING
NODE
C2
0.1µF
C1
0.1µF
R1
1M
FROM
FILTER
OUTPUT
R2
1M
C1 = C2 = LOW LEAKAGE FILM (I.E. POLYPROPYLENE)
R1 = R2 = METAL FILM 1%
–
+
LT1012
ODES OF OPERATIO
U
W
LTC1164 • MOO01
R3
R2
NS BPLP
R1
AGND
1/4 LTC1164
f
o
= Q =; f
n
= f
O
; H
OLP
= – ; H
OBP
= – ; H
ON1
= –
f
CLK
100(50)
–
+
+
–
Σ
∫
∫
V
IN
R2
R1
R2
R1
R3
R2
R3
R1
LTC1164 • AI02
0.1µF
R11
V
+
TRACE FOR FILTER
R21
R3
R22
R12
R32
1k
LTC1164
NEGATIVE
SUPPLY
POSITIVE
SUPPLY
4
7
7
19
–
+
V
IN
0.1µF
SEPARATE V
+
POWER SUPPLY TRACE FOR BUFFER
0.1µF
0.1µF1µF T
A
1µF T
A