Datasheet
18
LTC1060
1060fb
Figure 22. Combining Mode 3 with Mode 2b to Create a 4th
Order BR Elliptic Filter with 1dB Ripple and a Ratio of 0dB to
Stop Bandwidth Equal to 9/1.
Figure 23. Amplitude Response of the Notch Filter of Figure 22
Switched capacitor integrators generally exhibit higher
input offsets than discrete R, C integrators. These offsets
are mainly due to the charge injection of the CMOS
switches into the integrating capacitors and they are
temperature independent.
The internal op amp offsets also add to the overall offset
budget and they are typically a couple of millivolts. Be-
cause of this, the DC output offsets of switched capacitor
filters are usually higher than the offsets of discrete active
filters.
Figure 24 shows half of an LTC1060 filter building block
with its equivalent input offsets V
OS1
, V
OS2
, V
OS3
. All three
are 100% tested for both sides of the LTC1060. V
OS2
is
generally the larger offset. When the S
A/B
, Pin 6, of the
LTC1060 is shorted to the negative supply (i.e., mode 3),
the value of the V
OS2
decreases. Additionally, with S
A/B
low, a 20% to 30% noise reduction is observed. Mode 1
can still be achieved, if desired, by shorting the S1 pin to
the lowpass output (Figure 25).
LTC1060 • CM04
V
IN
R31
R21
R52
R32
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
V
+
= –5V
–5V
V
OUT
T
2
L OR CMOS
CLOCK IN
R41
R
L1
R
H1
R22
R62
R42
LP
A
BP
A
HP
A
INV
A
S1A
S
A/B
V
A
+
V
D
+
LSh
CLK
A
LP
B
BP
B
N
B
INV
B
S1B
AGND
V
A
–
V
D
–
50/100
CLK
B
LTC1060
R11
RESISTOR VALUES
R11 = 60k
R41 = 28.84k
R52 = 5k
R32 = 455.75k
R21 = 5k
R
H1
= 5k
R62 = 1.59k
R42 = 503.85k
R31 = 54.75k
R
L1
= 19.3k
R22 = 60k
V
–
= –5V
0.7
–30
–20
–10
0
1.1 1.2 1.3
–60
–50
–40
0.9
0.8
f
0
= 1.0
V
OUT
/V
IN
(dB)
INPUT FREQUENCY NORMALIZED TO FILTER CENTER FREQUENCY
TLC1060 • CMO05
f
CLK
f
0
200
1
=; f
CLK
≤ 1MHz
+
(17)
4
++
–
–
–
–
–
+
(18) (16) (19) (20)
15
V
OS1
V
OS2
3 5
Σ
TLC1060 • LO01
1
2
–
+
–
+
+
–
V
OS3
Figure 24. Equivalent Input Offsets of 1/2 LTC1060 Filter
Building Block
Figure 25. Mode 1(LN): Same Operation as Mode 1 but Lower
V
OS2
Offset and Lower Noise
LTC1060 OFFSETS
COMM E TS ON THE M ODES OF OPERATIO
U
U
WWW
U
1/2 LTC1060
S
A/B
V
IN
1
+
–
–
–
+
R3
R2
R1
N
(18)
LP
(20)
BP
(19)
S1A
(16)
V
–
(17)
15
4
3 5
2
Σ
6
TLC1060 • LO02
∫
∫