C1068 Linear Technology, C1068 Datasheet - Page 12

• Manufacturer Part Number: C1068
• Description: Search -----> LTC1068
• Manufacturer: Linear Technology

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LTC1068 Series
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 parts nominal ratio. Figure 6
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 7. 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 de-
pends solely on the clock frequency and is therefore less
than the center frequency, f
Please refer to the Operating Limits paragraph under Appli-
cations Information for a guide to the use of capacitor C
12
MODES OF
CLK
V
IN
/f
Figure 5. Mode 1b, 2nd Order Filter Providing Notch,
Bandpass and Lowpass Outputs
O
R1
, is always less than the part’s nominal ratio. The
AGND
f
Q =
H
–
+
O
OLP
=
R3
R2
RATIO
R3
R2
f
= –
CLK
OPERATION
C
(R6 + R5)
R2
R1
C
R6
(R6 + R5)
R6 + R5
R6
R6
; H
R6
O
N
; f
ON
.
+
n
= –
= f
O
R2
R1
–
S
; H
R5
OBP
U
DEVICE
LTC1068
LTC1068-200
LTC1068-50
LTC1068-25
= –
R3
R1
BP
RATIO
1068 F05
100
200
50
25
C
LP
.
C
.
V
IN
V
IN
H
Q = 1.005
H
f
OHPN
OBP
O
Figure 7. Mode 2, 2nd Order Filter Providing Highpass
Notch, Bandpass and Lowpass Outputs
=
AGND
R1
RATIO
= –
AGND
R1
f
= –
CLK
Figure 6. Mode 3, 2nd Order Section Providing
Highpass, Bandpass and Lowpass Outputs
R3
R1
R3
R2
R2
R1
1 +
(AC GAIN, f >> f
1–
1 +
f
(RATIO)(0.32)(R4)
O
H
DEVICE
LTC1068
LTC1068-200
LTC1068-50
LTC1068-25
R2
R4
–
+
OHP
=
–
+
R2
R4
; f
RATIO
R4
R3
R2
f
n
CLK
= –
=
1
R4
R3
R2
R3
RATIO
1–
R2
R1
f
CLK
O
(RATIO)(0.32)(R4)
; H
R2
R4
); H
RATIO
OBP
; Q = 1.005
100
200
OHPN
50
25
1/4 LTC1068
1
R3
= –
; H
HP
= –
+
HPN
R3
R1
OLP
C
+
C
C
R2
R1
C
= –
R3
R2
–
1 –
S
–
R2
R1
1 +
S
(RATIO)(0.32)(R4)
1
R2
R4
R2
R4
1 +
1
1
DEVICE
LTC1068
LTC1068-200
LTC1068-50
LTC1068-25
R3
1 –
R2
R4
(DC GAIN)
(RATIO)(0.32)(R4)
BP
BP
1
R3
; H
1068 F06
RATIO
1068 F07
OLP
100
200
50
25
= –
LP
LP
R4
R1