LTC1062
5th Order Lowpass Filter
FEATURES
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DESCRIPTIO
Lowpass Filter with No DC Error
Low Passband Noise
Operates DC to 20kHz
Operates On a Single 5V Supply or Up to
±8V
5th Order Filter
Maximally Flat Response
Internal or External Clock
Cascadable for Faster Rolloff
Buffer Available
The LTC
®
1062 is a 5th order all pole maximally flat
lowpass filter with no DC error. Its unusual architecture
puts the filter outside the DC path so DC offset and low
frequency noise problems are eliminated. This makes the
LTC1062 very useful for lowpass filters where DC accuracy
is important.
The filter input and output are simultaneously taken across
an external resistor. The LTC1062 is coupled to the signal
through an external capacitor. This RC reacts with the
internal switched capacitor network to form a 5th order
rolloff at the output.
The filter cutoff frequency is set by an internal clock that
can be externally driven. The clock-to-cutoff frequency
ratio is typically 100:1, allowing the clock ripple to be
easily removed.
Two LTC1062s can be cascaded to form a 10th order quasi
max flat lowpass filter. The device can be operated with
single or dual supplies ranging from
±2.5V
to
±9V.
The LTC1062 is manufactured using Linear Technology’s
enhanced LTCMOS
TM
silicon gate process.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS is a trademark of Linear Technology Corporation.
APPLICATIO S
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60Hz Lowpass Filters
Antialiasing Filter
Low Level Filtering
Rolling Off AC Signals from High DC Voltages
Digital Voltmeters
Scales
Strain Gauges
TYPICAL APPLICATIO
25.8k
V
IN
1µF
1
2
FB
AGND
V
–
B
OUT
OUT
V
+
10Hz 5th Order Butterworth Lowpass Filter
DC ACCURATE
OUTPUT
8
7
BUFFERED
OUTPUT
Filter Amplitude Response and Noise
0
–10
C
OSC
= 3900pF
AMPLITUDE RESPONSE (dB)
–20
–30
–40
–50
–60
–70
–80
–90
50
40
30
20
10
1
10
INPUT FREQUENCY (Hz)
0
100
1062 TA02
LTC1062
V
–
= –5V
3
4
6
5
DIVIDER C
OSC
RATIO
C
OSC=
3900pF
V
+
= 5V
1062 TA01
–100
NOTE: TO ADJUST OSCILLATOR FREQUENCY,
USE A 6800pF CAPACITOR IN SERIES
WITH A 50k POT FROM PIN 5 TO GROUND
U
FILTER OUTPUT NOISE (µV/√Hz)
1062fd
U
U
1
LTC1062
ABSOLUTE
AXI U
RATI GS
Total Supply Voltage (V
+
to V
–
) ............................... 18V
Input Voltage at Any Pin ..... V
–
– 0.3V
≤
V
IN
≤
V
+
+ 0.3V
Operating Temperature Range
LTC1062M
(OBSOLETE)
............. –55°C
≤
T
A
≤
125°C
LTC1062C ................................... – 40°C
≤
T
A
≤
85°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
FB 1
AGND 2
V
–
8
7
6
5
N8 PACKAGE
8-LEAD PDIP
B
OUT
OUT
V
+
ORDER PART
NUMBER
LTC1062CN8
3
DIVIDER 4
RATIO
C
OSC
T
J MAX
= 100°C,
θ
JA
= 130°C/W
J8 PACKAGE 8-LEAD CERDIP
T
J MAX
= 150°C,
θ
JA
= 100°C/W
LTC1062MJ8
LTC1062CJ8
OBSOLETE PACKAGE
Consider the N8 Package as an Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
+
PARAMETER
Power Supply Current
Input Frequency Range
Filter Gain at f
IN
= 0
f
IN
= 0.5f
C
(Note 2)
f
IN
= f
C
f
IN
= 2f
C
f
IN
= 4f
C
Clock-to-Cutoff Frequency Ratio, f
CLK
/f
C
Filter Gain at f
IN
= 16kHz
f
CLK
/f
C
Tempco
Filter Output (Pin 7, Pin 13 in SW16) DC Swing
Clock Feedthrough
CONDITIONS
The
●
denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25°C. V = 5V, V
–
= – 5V, unless otherwise specified. AC output measured at Pin 7,
Figure 1.
MIN
●
C
OSC
(Pin 5 to V
–
, Pin 11 in SW16) = 100pF
f
CLK
= 100kHz, Pin 4 (Pin 6 in SW16) at V
+
,
C = 0.01µF, R = 25.78k
●
●
●
f
CLK
= 100kHz, Pin 4 (Pin 6 in SW16) at V
+
,
C = 0.01µF, R = 25.78k
f
CLK
= 400kHz, Pin 4 at V
+
, C = 0.01µF, R = 6.5k
f
CLK
= 400kHz, Pin 4 at V
+
, C = 0.01µF, R = 6.5k
Pin 7/Pin13 (SW16) Buffered with an External Op Amp
●
●
2
U
U
W
W W
U
W
(Note 1)
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
TOP VIEW
NC 1
NC 2
FB 3
AGND 4
V– 5
DIVIDER
6
RATIO
NC 7
NC 8
SW PACKAGE
16-LEAD PLASTIC SO
16 NC
15 NC
14 B
OUT
13 OUT
12 V
+
11 C
OSC
10 NC
9
NC
ORDER PART
NUMBER
LTC1062CSW
T
J MAX
= 150°C,
θ
JA
= 90°C/W
TYP
4.5
0 to 20
MAX
7
10
UNITS
mA
mA
kHz
dB
dB
dB
dB
dB
%
dB
ppm/°C
V
mV
P-P
–2
–28
–52
0.00
– 0.02 –0.3
–3.00
–30.00
–60.00
100
±1
–43
±3.5
–52
10
±3.8
1
1062fd
LTC1062
ELECTRICAL CHARACTERISTICS
+
PARAMETER
Internal Buffer
Bias Current
CONDITIONS
The
●
denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at T
A
= 25°C. V = 5V, V
–
= – 5V, unless otherwise specified, AC output measured at Pin 7,
Figure 1.
MIN
TYP
2
170
2
R
LOAD
= 20k
●
MAX
50
1000
20
UNITS
pA
pA
mV
V
mA
●
Offset Voltage
Voltage Swing
Short-Circuit Current Source/Sink
Clock (Note 3)
Internal Oscillator Frequency
Max Clock Frequency
Pin 5 (Pin 11 in SW16) Source or Sink Current
Note 1:
Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2:
f
C
is the frequency where the gain is –3dB with respect to the input
signal.
●
±3.5
±3.8
40/3
C
OSC
(Pin 5 to V
–
, Pin 11 in SW16) = 100pF
●
25
15
32
4
40
50
65
80
kHz
kHz
MHz
µA
Note 3:
The external or driven clock frequency is divided by either 1, 2 or 4
depending upon the voltage at Pin 4. For the N8 package, when Pin 4 = V
+
,
ratio = 1; when Pin 4 = GND, ratio = 2; when Pin 4 = V
–
, ratio = 4.
TYPICAL PERFOR A CE CHARACTERISTICS
Amplitude Response Normalized
to the Cutoff Frequency
0
–10
–20
RESPONSE (dB)
V
S
=
±2.5V
T
A
= 25°C
1 = f
C
2πRC 1.62
RESPONSE (dB)
–30
–40
–50
–60
–70
–80
–90
f
CLK
= 10kHz, f
C
= 100Hz
f
CLK
= 1kHz, f
C
= 10Hz
1
f
IN
/f
C
10
1062 G01
–30
–40
–50
–60
–70
–80
–90
f
CLK
= 10kHz, f
C
= 100Hz
f
CLK
= 1kHz, f
C
= 10Hz
1
f
IN
/f
C
10
1062 G01
PASSBAND GAIN (dB)
f
CLK
= 500kHz, f
C
= 5kHz
f
CLK
= 250kHz, f
C
= 2.5kHz
f
CLK
= 100kHz, f
C
= 1kHz
–100
0.1
U W
Amplitude Response Normalized
to the Cutoff Frequency
0
–10
–20
V
S
=
±2.5V
T
A
= 25°C
1 = f
C
2πRC 1.62
Passband Gain
vs Input Frequency
0.4
V
S
=
±5V
T
A
= 25°C
0.2 f
CLK
= 100kHz
0
–0.2
–0.4
–0.6
–0.8
–1.0
0.1
1 = f
C
2πRC 1.62
1 = f
C
2πRC 1.64
1 = f
C
2πRC 1.6
f
CLK
= 500kHz, f
C
= 5kHz
f
CLK
= 250kHz, f
C
= 2.5kHz
f
CLK
= 100kHz, f
C
= 1kHz
–100
0.1
0.2
f
IN
/f
C
0.4
0.6
0.8
1
1062 G03
1062fd
3
LTC1062
TYPICAL PERFOR A CE CHARACTERISTICS
Passband Gain
vs Input Frequency and Temperature
0.4
V
S
=
±5V
f
CLK
= 100kHz
0.2
1 = f
C
2πRC 1.62
0
–0.2
–0.4
–0.6
–0.8
–1.0
0.1
0
–30
T
A
= 125°C
T
A
= –55°C
PHASE SHIFT (DEG)
FILTER OUTPUT NOISE (µV/√Hz)
PASSBAND GAIN (dB)
0.2
f
IN
/f
C
0.4
Normalized Oscillator Frequency,
f
OSC
vs Supply Voltage
1.6
OSCILLATOR FREQUENCY NORMALIZED
TO f
OSC
AT 5V SUPPLY
1.5
OSCILLATOR FREQUENCY (kHz)
SUPPLY CURRENT (mA)
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
4
6
8
10
14
V
SUPPLY
(V)
12
16
18
20
4
U W
0.6
0.8
Passband Phase Shift
vs Input Frequency
V
S
=
±5V
f
CLK
= 100kHz
1 = f
C
2πRC 1.62
T
A
= 25°C
Filter Noise Spectral Density
80
70
60
50
f
C
= 10Hz
40
30
20
10
f
C
= 100Hz
f
C
= 1kHz
1
1k
10
100
CUTOFF FREQUENCY (Hz)
10k
1062 G06
V
S
=
±5V
T
A
= 25°C
–60
–90
–120
–150
–180
–210
0.1
1
0.2
f
IN
/f
C
0.4
0.6
0.8
1
0
0.1
1062 G04
1062 G05
Oscillator Frequency, f
OSC
vs Ambient Temperature
260
240
220
200
180
160
140
120
100
80
V
+
= 5V
V
–
= 0V
V
+
= 10V
V
–
= 0V
12
10
8
6
4
2
0
Power Supply Current
vs Power Supply Voltage
16
14
T
A
= –55°C
T
A
= 25°C
C
OSC
= 0pF
T
A
= 125°C
60
25 50
–50 –25
0
75 100
AMBIENT TEMPERATURE (°C)
125
4
6
8
10 12 14 16 18
POWER SUPPLY VOLTAGE (V)
20
1062 G07
1062 G08
1062 G09
1062fd
LTC1062
BLOCK DIAGRA
W
SWITCHED
CAPACITOR
NETWORK
×1
f
CLK
V
–
3
CLOCK GEN
6
V
+
8
B
OUT
7
OUT
÷
1, 2, 4
OSC
5
C
OSC
1062 BD
For Adjusting Oscillator Frequency, Insert a 50k Pot in Series with C
OSC
. Use Two Times Calculated C
OSC
BY CONNECTING PIN 4 TO V
+
, AGND OR V
–
, THE
OUTPUT FREQUENCY OF THE INTERNAL CLOCK
GENERATOR IS THE OSCILLATOR FREQUENCY DI-
VIDED BY 1, 2, 4. THE (f
CLK
/f
C
) RATIO OF 100:1 IS
WITH RESPECT TO THE INTERNAL CLOCK GENERA-
TOR OUTPUT FREQUENCY. PIN 5 CAN BE DRIVEN
WITH AN EXTERNAL CMOS LEVEL CLOCK. THE
LTC1062 CAN ALSO BE SELF-CLOCKED BY CON-
NECTING AN EXTERNAL CAPACITOR (C
OSC
) TO
GROUND (OR TO V
–
IF C
OSC
IS POLARIZED). UNDER
THIS CONDITION AND WITH
±5V
SUPPLIES, THE
INTERNAL OSCILLATOR FREQUENCY IS:
f
OSC
≅
140kHz [33pF/(33pF + C
OSC
)]
FB
1
AGND
2
÷
4
AC TEST CIRCUIT
5V
V
IN
R = 25.8k
C = 0.01µF
50Ω
1
2
FB
AGND
V
–
B
OUT
OUT
V
+
8
7
0.1µF
R′
–5V
5V
5V
–5V
f
CLK
= 100kHz
2
3
+
–
1
7
LTC1052
8
4
6
MEASURED
OUTPUT
FOR BEST MAX FLAT APPROXIMATION,
THE INPUT RC SHOULD BE SUCH AS:
1 = f
CLK
1
•
2πRC 100
1.63
0.1µF
A 0.5k RESISTOR, R′, SHOULD BE USED IF
THE BIPOLAR EXTERNAL CLOCK IS APPLIED
BEFORE THE POWER SUPPLIES TURN ON
LTC1062
V
–
= –5V
3
4
6
5
DIVIDER C
OSC
RATIO
1062 F01
Figure 1
1062fd
5
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