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PDF LTC1062 Data sheet ( Hoja de datos )
| Número de pieza | LTC1062 | |
| Descripción | 5th Order Lowpass Filter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1062
5th Order Lowpass Filter
FEATURES
■ 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
U
APPLICATIO S
■ 60Hz Lowpass Filters
■ Antialiasing Filter
■ Low Level Filtering
■ Rolling Off AC Signals from High DC Voltages
■ Digital Voltmeters
■ Scales
■ Strain Gauges
TYPICAL APPLICATIO
10Hz 5th Order Butterworth Lowpass Filter
25.8k
VIN
V– = –5V
1µF
1
FB
2
AGND
8
BOUT
7
OUT
DC ACCURATE
OUTPUT
BUFFERED
OUTPUT
LTC1062
3 V–
V+ 6
45
DIVIDER COSC
RATIO
COSC=
3900pF
V+ = 5V
1062 TA01
NOTE: TO ADJUST OSCILLATOR FREQUENCY,
USE A 6800pF CAPACITOR IN SERIES
WITH A 50k POT FROM PIN 5 TO GROUND
DESCRIPTIO
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 LTCMOSTM silicon gate process.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS is a trademark of Linear Technology Corporation.
Filter Amplitude Response and Noise
0
COSC = 3900pF
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
1
10
INPUT FREQUENCY (Hz)
50
40
30
20
10
0
100
1062 TA02
1062fd
1
1 page  
BLOCK DIAGRA
LTC1062
For Adjusting Oscillator Frequency, Insert a 50k Pot in Series with COSC. Use Two Times Calculated COSC
FB 1
AGND 2
V– 3
÷4
SWITCHED
CAPACITOR
NETWORK
fCLK
CLOCK GEN
÷ 1, 2, 4
8 BOUT
×1 7 OUT
6 V+
OSC
5 COSC
1062 BD
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 (fCLK/fC) 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 (COSC) TO
GROUND (OR TO V– IF COSC IS POLARIZED). UNDER
THIS CONDITION AND WITH ±5V SUPPLIES, THE
INTERNAL OSCILLATOR FREQUENCY IS:
fOSC ≅ 140kHz [33pF/(33pF + COSC)]
AC TEST CIRCUIT
VIN R = 25.8k
C = 0.01µF
50Ω
1
FB
8
BOUT
2
AGND
7
OUT
V– = –5V
LTC1062
3 V–
V+
4
DIVIDER COSC
RATIO
6
5
5V
3+ 7
LTC1052
2– 4
1
0.1µF
R′ 5V
–5V
fCLK = 100kHz
5V
1062 F01
–5V
6 MEASURED
8 OUTPUT
0.1µF
FOR BEST MAX FLAT APPROXIMATION,
THE INPUT RC SHOULD BE SUCH AS:
1=
2πRC
fCLK
100
•
1
1.63
A 0.5k RESISTOR, R′, SHOULD BE USED IF
THE BIPOLAR EXTERNAL CLOCK IS APPLIED
BEFORE THE POWER SUPPLIES TURN ON
Figure 1
1062fd
5
5 Page 
TYPICAL APPLICATIO S
LTC1062
7th Order 100Hz Lowpass Filter with Continuous Output Filtering, Output Buffering and Gain Adjustment
R3 R4
2.6k
VIN
R1
1µF
1
FB
2
AGND
8
BOUT
7
OUT
LTC1062
–5V 3 V–
V+ 6 5V
5V 4 DIVIDER COSC 5 10kHz
RATIO
CLK IN
R2
C1
5V
2
–
7
LTC1052
3+
C2 1
4
0.1µF
6
8
0.1µF
–5V
VOUT
1062 TA13
THE LTC1052 IS CONNECTED AS A 2ND ORDER SALLEN AND KEY LOWPASS FILTER WITH A CUTOFF
FREQUENCY EQUAL TO THE CUTOFF FREQUENCY OF THE LTC1062. THE ADDITIONAL FILTERING
ELIMINATES ANY 10kHz CLOCK FEEDTHROUGH PLUS DECREASES THE WIDEBAND NOISE OF THE FILTER
DC OUTPUT OFFSET (REFERRED TO A DC GAIN OF UNITY) = 5µV MAX
WIDEBAND NOISE (REFERRED TO A DC GAIN OF UNITY) = 60µVRMS
OUTPUT FILTER COMPONENT VALUES
DC GAIN R3 R4 R1 R2 C1
C2
1 ∞ 0 14.3k 53.6k 0.1µF 0.033µF
10 3.57k 32.4k 46k 274k 0.01µF 0.02µF
Single 5V Supply 5th Order LP Filter
10µF
5V VIN
SOLID
TANTALUM 25k
25k
R
C
1
FB
2
AGND
8
BOUT
7
BUFFERED
OUTPUT
OUT
LTC1062
3 V–
V+ 6 5V
5V 4 DIVIDER COSC 5 CLK
RATIO
DC ACCURATE
C OUTPUT
12R
1062 TA14
FOR A 10Hz FILTER: R = 29.4k, C = 1µF, fCLK = 1kHz
THE
FILTER
IS
MAXIMALLY
FLAT
FOR
1
2πRC
=
fC
1.84
1062fd
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1062.PDF ] | |
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