LTC1067 Linear Technology, LTC1067 Datasheet - Page 10

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

LTC1067/LTC1067-50
The parallel combination of R5 and R6 should be kept
below 5k.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C
Mode 3
In Mode 3, the ratio of the external clock frequency to the
center frequency of each 2nd order section can be ad-
justed above or below the part’s nominal ratio. Figure 5
illustrates Mode 3, the classical state variable configura-
tion, providing highpass, bandpass and lowpass 2nd
order filter functions. Mode 3 is slower than Mode 1. Mode
3 can be used to make high order all-pole bandpass,
lowpass and highpass filters.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C
Mode 2
Mode 2 is a combination of Mode 1 and Mode 3, shown in
Figure 6. With Mode 2, the clock-to-center frequency ratio,
f
advantage of Mode 2 is that it provides less sensitivity to
resistor tolerances than does Mode 3. Mode 2 has a
highpass-notch output where the notch frequency
depends solely on the clock frequency and is therefore
less than the center frequency, f
10
W
CLK
V
NOTE: RATIO = 100 FOR LTC1067
IN
ODES OF OPERATIO
/f
Figure 4. Mode 1b, 2nd Order Filter Providing Notch,
Bandpass and Lowpass Outputs
O
R1
, is always less than the part’s nominal ratio. The
= 50 FOR LTC1067-50
AGND
–
+
R3
R2
C
C
f
Q =
H
O
R6
OLP
N
=
R3
R2
RATIO
+
f
= –
CLK
O
(R6 + R5)
R2
R1
.
–
S
(R6 + R5)
R6
R6 + R5
R5
R6
R6
U
; H
; f
ON
n
= –
= f
O
BP
R2
R1
; H
OBP
1067 F04
= –
C
R3
R1
LP
.
C
.
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C
V
V
IN
IN
Figure 6. Mode 2, 2nd Order Filter Providing Highpass
Notch, Bandpass and Lowpass Outputs
AGND
R1
AGND
R1
H
NOTE: RATIO = 100 FOR LTC1067
H
Figure 5. Mode 3, 2nd Order Section Providing
Highpass, Bandpass and Lowpass Outputs
Q = 1.005
f
OBP
OHPN
O
=
RATIO
= –
f
= –
CLK
H
NOTE: RATIO = 100 FOR LTC1067
–
+
f
O
–
R3
R1
OHP
+
R3
R2
=
R2
R1
RATIO
= 50 FOR LTC1067-50
R4
R3
R2
f
= –
R4
R3
R2
1 +
CLK
(AC GAIN, f >> f
1 –
1 +
R2
R1
R2
R4
(RATIO)(0.32)(R4)
; H
= 50 FOR LTC1067-50
R2
R4
R2
R4
; f
OBP
n
1
; Q = 1.005
=
R3
1 –
RATIO
= –
f
HP
CLK
HPN
O
(RATIO)(0.32)(R4)
+
R3
R1
); H
C
C
C
+
C
OHPN
1
1 –
–
R3
R2
S
R3
; H
–
(RATIO)(0.32)(R4)
S
= –
OLP
R2
R4
R2
R1
1
= –
R3
1 –
1 +
R2
R1
1
(RATIO)(0.32)(R4)
R2
R4
BP
1 +
BP
1
1
(DC GAIN)
R2
R4
R3
;
H
OLP
1067 F05
1067 F06
= –
LP
C
LP
R4
R1
.