LTC1067 Linear Technology, LTC1067 Datasheet - Page 11

• Manufacturer Part Number: LTC1067
• Description: Rail-to-Rail/ Very Low Noise Universal Dual Filter Building Block
• Manufacturer: Linear Technology

Mode 3a
This is an extension of Mode 3 where the highpass and
lowpass outputs are summed through two external resis-
tors, R
is more versatile than Mode 2 because the notch fre-
quency can be higher or lower than the center frequency
of the 2nd order section. The external op amp of Figure 7
is not always required. When cascading the sections of the
LTC1067, the highpass and lowpass outputs can be
summed directly into the inverting input of the next
section.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C
W
ODES OF OPERATIO
H
and R
V
V
IN
IN
R1
L
R1
, to create a notch (see Figure 7). Mode 3a
Figure 7. Mode 3a, 2nd Order Filter Providing a Highpass Notch or Lowpass Notch Output
AGND
AGND
–
+
–
+
R4
R3
R2
R4
R3
R2
Figure 8. Mode 2n, 2nd Order Filter Providing a Lowpass Notch Output
HP
HP
+
+
C
C
C
C
U
–
–
S
S
R
R
H
H
BP
BP
C
.
LP
LP
R
R
Mode 2n
This mode extends the circuit topology of Mode 3a to
Mode 2 (Figure 8) where the highpass-notch and lowpass
outputs are summed through two external resistors, R
and R
frequency than the notch in Mode 2. This mode, shown in
Figure 8, is most useful in lowpass elliptic designs. When
cascading the sections of the LTC1067, the highpass-
notch and lowpass outputs can be summed directly into
the inverting input of the next section.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C
L
L
Q = 1.005 R3
NOTE: RATIO = 100 FOR LTC1067
f
H
O
f
f
H
Q = 1.005
NOTE: RATIO = 100 FOR LTC1067
OHPn
O
n
L
OLPn
=
=
, to create a lowpass output with a notch higher in
=
–
+
–
+
RATIO
RATIO
RATIO
f
f
CLK
f
CLK
(f = ) =
CLK
(f = 0)=
R
R2
R3
R2
R
G
EXTERNAL OP AMP OR INPUT OP
AMP OF THE LTC1067, SIDES A OR B
= 50 FOR LTC1067-50
G
EXTERNAL OP AMP OR INPUT OP AMP
OF THE LTC1067, SIDES A OR B
R2
R4
1 +
1 +
= 50 FOR LTC1067-50
R
R
R2
R4
;
R
R
R
R
G
H
1 +
R2
R4
f
G
H
n
H
L
+
=
LTC1067/LTC1067-50
R
R
R2
R4
R2
R1
RATIO
1 –
G
f
L
CLK
(RATIO)(0.32)(R4)
; H
R2
R1
1 –
LOWPASS
NOTCH
OUTPUT
HIGHPASS
OR LOWPASS
NOTCH OUTPUT
OLPn
R
(RATIO)(0.32)(R4)
R
1
1 +
H
L
R3
(f = 0) =
1
R2
R4
1
R3
R
R
G
L
R4
R1
1067 F08
1067 F07
11
C
.
H