LINEAR TECHNOLOGY LTC1062 Technical data

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

LTC1062

5th Order Lowpass Filter

U

DESCRIPTIO

®

The LTC
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.

1062 is a 5th order all pole maximally flat

TYPICAL APPLICATIO

10Hz 5th Order Butterworth Lowpass Filter Filter Amplitude Response and Noise

25.8k

V

V

–

= –5V

IN

1µF

1

FB

2

AGND

3

V

4

DIVIDER
RATIO

NOTE: TO ADJUST OSCILLATOR FREQUENCY,
USE A 6800pF CAPACITOR IN SERIES
WITH A 50k POT FROM PIN 5 TO GROUND

LTC 1062

–

B

C

OUT

OUT

OSC

+

V

The LTC1062 is manufactured using Linear Technology’s
enhanced LTCMOS

, LTC and LT are registered trademarks of Linear Technology Corporation.

LTCMOS is a trademark of Linear Technology Corporation.

TM

silicon gate process.

U

DC ACCURATE
OUTPUT

8

7

6

5

C

OSC=

3900pF

BUFFERED
OUTPUT

1062 TA01

+

= 5V

V

0

C

= 3900pF

OSC

–10

–20

–30

–40

–50

–60

–70

AMPLITUDE RESPONSE (dB)

–80

–90

–100

1

INPUT FREQUENCY (Hz)

10 100

1062 TA02

FILTER OUTPUT NOISE (µV/√Hz)

50

40

30

20

10

0

1062fd

1

LTC1062

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Total Supply Voltage (V+ to V–) ............................... 18V

–

Input Voltage at Any Pin ..... V

– 0.3V ≤ VIN ≤ V+ + 0.3V

Operating Temperature Range

LTC1062M (OBSOLETE)............. –55°C ≤ T

LTC1062C ................................... – 40°C ≤ T

UU

W

≤ 125°C

A

≤ 85°C

A

PACKAGE/ORDER I FOR ATIO

TOP VIEW

FB

1

AGND

2

–

V

3

DIVIDER

4

RATIO

N8 PACKAGE
8-LEAD PDIP

T

= 100°C, θ

J MAX

J8 PACKAGE 8-LEAD CERDIP

T

= 150°C, θ

J MAX

Consider the N8 Package as an Alternate Source

B

8

OUT

OUT

7

+

V

6

C

5

OSC

= 130°C/W

JA

= 100°C/W

JA

OBSOLETE PACKAGE

ORDER PART

NUMBER

LTC1062CN8

LTC1062MJ8
LTC1062CJ8

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)................. 300°C

ORDER PART

NUMBER

LTC1062CSW

NC

NC

AGND

DIVIDER

RATIO

NC

NC

1

2

3

FB

4

5

V–

6

7

8

SW PACKAGE

16-LEAD PLASTIC SO

T

= 150°C, θ

J MAX

TOP VIEW

JA

= 90°C/W

16

NC

15

NC

14

B

OUT

13

OUT

+

12

V

11

C

OSC

10

NC

9

NC

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The

● denotes specifications which apply over the full operating tempera-

ture range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = – 5V, unless otherwise specified. AC output measured at Pin 7,
Figure 1.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Power Supply Current C

Input Frequency Range 0 to 20 kHz

Filter Gain at fIN = 0 f

= 0.5fC (Note 2) C = 0.01µF, R = 25.78k –0.02 –0.3 dB

f

IN

f

= f

IN

C

= 2f

f

IN

C

= 4f

f

IN

C

Clock-to-Cutoff Frequency Ratio, f

CLK/fC

Filter Gain at fIN = 16kHz f

f

Tempco f

CLK/fC

Filter Output (Pin 7, Pin 13 in SW16) DC Swing Pin 7/Pin13 (SW16) Buffered with an External Op Amp ● ±3.5 ±3.8 V

Clock Feedthrough 1mV

(Pin 5 to V–, Pin 11 in SW16) = 100pF 4.5 7 mA

OSC

= 100kHz, Pin 4 (Pin 6 in SW16) at V+, 0.00 dB

CLK

f

= 100kHz, Pin 4 (Pin 6 in SW16) at V+,100 ±1%

CLK

● 10 mA

● –2 –3.00 dB

● –28–30.00 dB

● –52–60.00 dB

C = 0.01µF, R = 25.78k

= 400kHz, Pin 4 at V+, C = 0.01µF, R = 6.5k ● –43 –52 dB

CLK

= 400kHz, Pin 4 at V+, C = 0.01µF, R = 6.5k 10 ppm/°C

CLK

P-P

2

1062fd

LTC1062

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating tempera-

ture range, otherwise specifications are at TA = 25°C. V+ = 5V, V– = – 5V, unless otherwise specified, AC output measured at Pin 7,
Figure 1.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Internal Buffer

Bias Current 250 pA

● 170 1000 pA

Offset Voltage 220 mV

Voltage Swing R

Short-Circuit Current Source/Sink 40/3 mA

Clock (Note 3)

Internal Oscillator Frequency C

Max Clock Frequency 4 MHz
Pin 5 (Pin 11 in SW16) Source or Sink Current ● 40 80 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.

Note 2: f

is the frequency where the gain is –3dB with respect to the input

C

signal.

= 20k ● ±3.5 ±3.8 V

LOAD

(Pin 5 to V–, Pin 11 in SW16) = 100pF 25 32 50 kHz

OSC

● 15 65 kHz

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.

+

,

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Amplitude Response Normalized
to the Cutoff Frequency

0

= ±2.5V

V

S

= 25°C

T

–10

A

f

1

C

0.1

2πRC

=

1.62

f

CLK

f

CLK

= 500kHz, fC = 5kHz
= 250kHz, fC = 2.5kHz

f

= 100kHz, fC = 1kHz

CLK

f

= 10kHz, fC = 100Hz

CLK

f

= 1kHz, fC = 10Hz

CLK

110

fIN/f

C

–20

–30

–40

–50

–60

RESPONSE (dB)

–70

–80

–90

–100

1062 G01

Amplitude Response Normalized
to the Cutoff Frequency

0

V

= ±2.5V

S

= 25°C

T

–10

A

f

1

C

0.1

2πRC

f

=

f

CLK

1.62

CLK

= 500kHz, fC = 5kHz
= 250kHz, fC = 2.5kHz

f

= 100kHz, fC = 1kHz

CLK

f

= 10kHz, fC = 100Hz

CLK

f

= 1kHz, fC = 10Hz

CLK

110

fIN/f

C

–20

–30

–40

–50

–60

RESPONSE (dB)

–70

–80

–90

–100

1062 G01

Passband Gain
vs Input Frequency

0.4
VS = ±5V

= 25°C

T

A

0.2

= 100kHz

f

CLK

0

–0.2

–0.4

–0.6

PASSBAND GAIN (dB)

–0.8

–1.0

0.1 0.2 0.4 0.6 0.8

1

2πRC

=

2πRC

f

1.62

C

1

fIN/f

f

C

=

1.6

1

2πRC

C

f

C

=

1.64

1

1062 G03

1062fd

3

LTC1062

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Passband Gain
vs Input Frequency and Temperature

0.4
VS = ±5V

f

= 100kHz

CLK

0.2

0

–0.2

–0.4

–0.6

PASSBAND GAIN (dB)

–0.8

–1.0

0.1 0.2 0.4 0.6 0.8

1

2πRC

f

C

=

1.62

TA = 125°C

TA = –55°C

fIN/f

C

Normalized Oscillator Frequency,
f

vs Supply Voltage

OSC

1.6

1.5

1.4

1.3

1.2

AT 5V SUPPLY

1.1

OSC

1.0

TO f

0.9

0.8

OSCILLATOR FREQUENCY NORMALIZED

0.7
4

8

6

10

V

12

SUPPLY

14

(V)

Passband Phase Shift
vs Input Frequency Filter Noise Spectral Density

80

VS = ±5V

= 25°C

T

A

70

60

50

40

30

20

FILTER OUTPUT NOISE (µV/√Hz)

10

0

0.1 10 100 10k

fC = 10Hz

fC = 100Hz

fC = 1kHz

1

CUTOFF FREQUENCY (Hz)

Power Supply Current
vs Power Supply Voltage

16

14

12

10

8

6

SUPPLY CURRENT (mA)

4

2

0

6

4

8

POWER SUPPLY VOLTAGE (V)

10

TA = –55°C

12

14

TA = 125°C

16

1k

1062 G06

TA = 25°C

18

1062 G09

20

1062 G04

1

0

–30

–60

–90

–120

PHASE SHIFT (DEG)

–150

–180

–210

0.1 0.2 0.4 0.6 0.8
fIN/f

Oscillator Frequency, f

VS = ±5V

= 100kHz

f

CLK

f

1

C

=

1.62

2πRC
TA = 25°C

1

C

1062 G05

OSC

vs Ambient Temperature

260

C

= 0pF

OSC

240

220

200

180

160

140

120

100

OSCILLATOR FREQUENCY (kHz)

80

18

16

20

1062 G07

60

–50

–25

V+ = 10V

–

= 0V

V

V+ = 5V

–

= 0V

V

50

25

0

AMBIENT TEMPERATURE (°C)

75

100

125

1062 G08

4

1062fd

BLOCK DIAGRA

LTC1062

W

For Adjusting Oscillator Frequency, Insert a 50k Pot in Series with C

FB

1

AGND

2

–

V

3

4

÷

AC TEST CIRCUIT

V

R = 25.8k

IN

C = 0.01µF

50Ω

V

–

= –5V

1

2

3

4

FB

AGND

–

V

DIVIDER
RATIO

SWITCHED

CAPACITOR

NETWORK

f

CLK

CLOCK GEN

÷ 1, 2, 4 OSC

8

B

OUT

7

OUT

LTC1062

6

+

V

5

C

OSC

R′

1062 F01

–5V

. Use Two Times Calculated C

OSC

BY CONNECTING PIN 4 TO V+, AGND OR V–, THE

B

8

OUT

×1

5V

f

= 100kHz

CLK

5V

7

6

5

1062 BD

0.1µF

OUT

V

C

3

2

+

OSC

+

LTC1052

–

1

–5V

OUTPUT FREQUENCY OF THE INTERNAL CLOCK
GENERATOR IS THE OSCILLATOR FREQUENCY DI­VIDED BY 1, 2, 4. THE (f
WITH RESPECT TO THE INTERNAL CLOCK GENERA­TOR OUTPUT FREQUENCY. PIN 5 CAN BE DRIVEN
WITH AN EXTERNAL CMOS LEVEL CLOCK. THE
LTC1062 CAN ALSO BE SELF-CLOCKED BY CON­NECTING AN EXTERNAL CAPACITOR (C
GROUND (OR TO V
THIS CONDITION AND WITH ±5V SUPPLIES, THE
INTERNAL OSCILLATOR FREQUENCY IS:

f

≅ 140kHz [33pF/(33pF + C

OSC

5V

7

6

MEASURED
OUTPUT

8

4

0.1µF

CLK/fC

–

IF C

IS POLARIZED). UNDER

OSC

FOR BEST MAX FLAT APPROXIMATION,
THE INPUT RC SHOULD BE SUCH AS:

1

2πRC

A 0.5k RESISTOR, R′, SHOULD BE USED IF
THE BIPOLAR EXTERNAL CLOCK IS APPLIED
BEFORE THE POWER SUPPLIES TURN ON

) RATIO OF 100:1 IS

)]

OSC

f

CLK

=

100

OSC

) TO

OSC

1

•

1.63

Figure 1

1062fd

5