LTC1164-6(Rev0) 查看數據表（PDF） - Linear Technology

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LTC1164-6
(Rev.:Rev0)

Low Power 8th Order Pin Selectable Elliptic or Linear Phase Lowpass Filter

Linear Technology 

LTC1164-6

PI FU CTIO S (14-Lead Dual-In-Line Package)

can be used provided that its input common-mode range

is well within the filter’s output swing. Pin 6 is an interme-

diate filter output providing an unspecified 6th order

lowpass filter. Pin 6 should not be loaded.

–

1k

+

LT1006, fC < 5kHz

LT1200, fC > 5kHz

1164-6 F03

Figure 3. Buffer for Filter Output

External Connection Pins (7, 14)

Pins 7 and 14 should be connected together. In a printed

circuit board the connection should be done under the IC

package through a short trace surrounded by the analog

ground plane.

NC Pin (1, 8, 13)

Pins 1, 8, and 13 are not connected to any internal circuit

point on the device and should preferably be tied to analog

ground.

APPLICATI S I FOR ATIO

Passband Response

The passband response of the LTC1164-6 is optimized for

a fCLK/fCUTOFF ratio of 100:1. Minimum passband ripple

occurs from 1Hz to 80% of fCUTOFF. Athough the passband

of the LTC1164-6 is optimized for ratio fCLK / fCUTOFF of

100:1, if a ratio of 50:1 is desired, connect a single pole

lowpass RC (f –3dB = 2 fCUTOFF) at the output of the filter.

The RC will make the passband gain response as flat as the

100:1 case. If the RC is omitted, and clock frequencies are

below 500kHz the passband gain will peak by 0.4dB at

90% fCUTOFF.

Table 2. Typical Passband Ripple with Single 5V Supply

(fCLK/fC) = 100:1, GND = 2V, 30kHz, Fixed Single Pole, Lowpass

RC Filter at Pin 9 (See Typical Applications)

PASSBAND

FREQUENCY

% of fCUTOFF

10

20

30

40

50

60

70

80

90

fCUTOFF

PASSBAND GAIN

(REFERENCED TO 0dB)

fCUTOFF = 1kHz

TA = 25°C

(dB)

fCUTOFF = 10kHz

TA = 0°C TA = 25°C TA = 70°C

(dB)

(dB)

(dB)

0.00

– 0.02

– 0.05

– 0.10

– 0.13

– 0.15

– 0.18

– 0.25

– 0.39

– 2.68

0.00

0.00

– 0.01

– 0.02

– 0.03

– 0.01

– 0.01

– 0.08

– 0.23

– 2.79

0.00

0.01

– 0.01

– 0.02

– 0.01

0.01

0.01

– 0.05

– 0.18

– 2.74

0.00

0.01

0.01

0.02

0.03

0.05

0.07

0.02

– 0.05

– 2.68

The gain peaking can approximate a sin χ/χ correction for

some applications. (See Typical Performance Characteris-

tics curve, Passband vs Frequency and fCLK at fCLK / fC =

50:1.)

When the LTC1164-6 operates with a single 5V supply and

its cutoff frequency is clock-tuned to 10kHz, an output

single pole RC filter can also help maintain outstanding

passband flatness from 0°C to 70°C. Table 2 shows

details.

Clock Feedthrough

Clock feedthrough is defined as, the RMS value of the clock

frequency and its harmonics that are present at the filter’s

output pin (9). The clock feedthrough is tested with the

input pin (2) grounded and, it depends on PC board layout

and on the value of the power supplies. With proper layout

techniques the values of the clock feedthrough are shown

in Table 3.

Table 3. Clock Feedthrough

VS

±2.5V

±5V

±7.5V

50:1

60µVRMS

100µVRMS

150µVRMS

100:1

60µVRMS

200µVRMS

500µVRMS

Note: The clock feedthrough at ±2.5V supplies is imbedded in the wideband

noise of the filter. (The clock signal is a square wave.)

8

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