Datasheet
11
LTC1067/LTC1067-50
ODES OF OPERATIO
U
W
Mode 3a
This is an extension of Mode 3 where the highpass and
lowpass outputs are summed through two external resis-
tors, R
H
and R
L
, to create a notch (see Figure 7). Mode 3a
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
C
.
Figure 7. Mode 3a, 2nd Order Filter Providing a Highpass Notch or Lowpass Notch Output
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
H
and R
L
, to create a lowpass output with a notch higher in
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
C
.
Figure 8. Mode 2n, 2nd Order Filter Providing a Lowpass Notch Output
–
+
Σ
∫ ∫
AGND
R1
HP
BP
LP
V
IN
1067 F07
+
–
S
R2
R3
R4
C
C
–
+
EXTERNAL OP AMP OR INPUT OP
AMP OF THE LTC1067, SIDES A OR B
HIGHPASS
OR LOWPASS
NOTCH OUTPUT
R
G
R
L
R
H
R2
R1
( )
R
G
R
H
()
f
O
=
;
f
n
=
H
OHPn
(f = ∞) = ; H
OLPn
(f = 0) =
f
CLK
RATIO
f
CLK
RATIO
√
R
H
R
L
√
R2
R4
Q = 1.005
R3
R2
√
R2
R4
( )
R4
R1
( )
R
G
R
L
()
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
R3
(RATIO)(0.32)(R4)
( )
1
1 –
–
+
Σ
∫ ∫
AGND
R1
HP
BP
LP
V
IN
1067 F08
+
–
S
R2
R3
R4
C
C
–
+
EXTERNAL OP AMP OR INPUT OP AMP
OF THE LTC1067, SIDES A OR B
LOWPASS
NOTCH
OUTPUT
R
G
R
L
R
H
f
O
=
f
n
=
H
OLPn
(f = 0)= +
f
CLK
RATIO
f
CLK
RATIO
√
R
H
R
L
1 +
R2
R1
R
G
R
L
R
G
R
H
()
1
R2
R4
1 +
( )
( )
√
R2
R4
1 +
Q = 1.005
R3
R2
( )
√
R2
R4
1 +
NOTE: RATIO = 100 FOR LTC1067
= 50 FOR LTC1067-50
R3
(RATIO)(0.32)(R4)
( )
1
1 –