LTC1064 Linear Technology, LTC1064 Datasheet - Page 10

• Manufacturer Part Number: LTC1064
• Description: Low Noise/ Fast/ Quad Universal Filter Building Block
• Manufacturer: Linear Technology

W
LTC1064
Mode 3a
This is an extension of Mode 3 where the highpass and
lowpass outputs are summed through two external resis-
tors R
9. Mode 3a is more versatile than Mode 2 because the
notch frequency can be higher or lower than the center
frequency of the 2nd order section. The external op amp of
Figure 9 is not always required. When cascading the
sections of the LTC1064, the highpass and lowpass out-
10
V
V
IN
IN
ODES OF OPERATIO
R1
R1
H
and R
AGND
AGND
–
+
L
R4
R3
R2
–
+
to create a notch. This is shown in Figure
R4
R3
R2
Figure 9. Mode 3a: 2nd Order Filter Providing Highpass, Bandpass, Lowpass and Notch
HP
+
C
C
Figure 8. Mode 2: 2nd Order Filter Providing Notch, Bandpass and Lowpass
–
S
N
1/4 LTC1064
+
1/4 LTC1064
R
–
H
S
U
BP
LP
BP
R
L
EXTERNAL OP AMP OR INPUT
OP AMP OF THE LTC1064,
SIDE A, B, C, D
+
–
1064 F08
R
LP
G
R3 =
MODE 2 (100:1):
MODE 2 (50:1):
NOTE: THE 50:1 EQUATIONS FOR MODE 2 ARE DIFFERENT FROM THE EQUATIONS
FOR MODE 2 OPERATION OF THE LTC1059, LTC1060 AND LTC1061. START WITH
f
O
, CALCULATE R2/R4, SET R4; FROM THE Q VALUE, CALCULATE R3:
MODE 3a (100:1):
MODE 3a (50:1):
puts can be summed directly into the inverting input of the
next section. The topology of Mode 3a is useful for elliptic
highpass and notch filters with clock-to-cutoff frequency
ratios higher than 100:1. This is often required to extend
the allowed input signal frequency range and to avoid
premature aliasing.
When the internal clock-to-center frequency ratio is set at
50:1, the design equations for Q and bandpass gain are
different from the 100:1 case .
1.005
NOTCH
Q
1064 F09
R2
1 +
R2
R4
H
H
f
f
O
O
OBP
OBP
+
f
H
H
f
H
NOTE: THE 50:1 EQUATIONS FOR MODE 3A ARE DIFFERENT FROM
THE EQUATIONS FOR MODE 3A OPERATION OF THE LTC1059,
LTC1060 AND LTC1061. START WITH f
FROM THE Q VALUE, CALCULATE R3:
R3 =
=
=
O
O
16R4
OLP
ON
OBP
f
100
f
R2
=
=
CLK
CLK
50
= –
= –
(f = f
f
f
100
CLK
CLK
50
1.005
= –
= –
1 –
Q
R3
R1
; THEN CALCULATE R1 TO SET THE DESIRED GAIN.
O
1 +
1 –
1 +
R4
R1
) = Q
R3
R1
; H
16R4
1 +
R3
R2
R4
R2
R3
R1
; H
16R4
R2
R4
ON1
R2
R4
R3
R2
R4
R2
R4
; f
ON1
R
; f
; H
R
(f
n
; f
G
L
+
n
=
; H
(f
; f
ON1
n
H
16R4
=
f
n
100
R2
=
0) = –
CLK
OLP
OLP
f
=
CLK
50
(f
0) =
f
f
CLK
50
CLK
(f = 0) =
50
–
SET THE DESIRED GAIN.
; THEN CALCULATE R1 TO
; Q =
0) = –
1 +
R
R
R
R
R
R
; Q =
G
H
H
G
R2
R1
L
L
; H
1.005
H
R2
R4
R
R
OHP
R4
R1
H
–
L
1 +
R3
R2
R2
OHP
R3
R4
R1
; H
R2
; H
R1
; H
; Q =
R2
R4
O
–
=
OHP
ON2
;
, CALCULATE R2/R4, SET R4;
ON2
1 +
Q =
–
1 +
16R4
R2
; H
R2
R1
f
R3
R2
f
R2
R4
ON2
R2
R4
f
1.005
; HOBP =
R2
R3
f
f
CLK
CLK
; H
= f
f
2
; H
2
–
CLK
R2
R4
2
OLP
16R4
OLP
R2
= –
=
R2
R4
=
–
= –
f
= –
–
CLK
2
R3
R1
R2
R2
R1
R
R
R1
1 +
G
H
1 +
;
;
R2
R1
=
1064 F08Eq
1064 F09Eq
R2
R1
R2
R1
R2
R4
–
R2
R4
R2
R1
;
;
;