LTC1164-8(RevA) 查看數據表（PDF） - Linear Technology

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LTC1164-8
(Rev.:RevA)

Ultraselective, Low Power 8th Order Elliptic Bandpass Filter with Adjustable Gain

Linear Technology 

LTC1164-8

APPLICATIONS INFORMATION

Passband Gain and Dynamic Range

The filter’s gain at fCENTER is set with an external op amp

and resistors RIN and RF (Figure 1). The filter’s center

frequency (fCENTER) is equal to the clock frequency divided

by 100. The output dynamic range of LTC1164-8 is opti-

mized for minimum noise and maximum voltage swing

when resistor RF is 61.9k. The value of resistor RIN

depends on the filter’s gain and it is calculated by the

equation RIN = 340k/Gain. Table 2 lists the values of RIN

and RF for some typical gains. Increasing the filter’s gain

with resistor RIN does not increase the noise generated by

the filter. Table 3 shows the noise generated by the filter

with its input grounded.

Table 2. Passband Gain at Center Frequency, RIN and RF

GAIN RIN (±1%) RF (±1%) GAIN IN dB RIN (±1%) RF (±1%)

1

340k

61.9k

0

340k

61.9k

2

169k

61.9k

10

107k

61.9k

5

68.1k

61.9k

15

60.4k

61.9k

10

34k

61.9k

20

34k

61.9k

20

16.9k

61.9k

25

19.1k

61.9k

50

6.81k

61.9k

30

10.7k

61.9k

100

3.4k

61.9k

35

6.01k

61.9k

200 1.69k

61.9k

40

3.4k

61.9k

500 680Ω

61.9k

45

1.91k

61.9k

1000 340Ω

61.9k

50

1.07k

61.9k

Table 3. LTC1164-8 Noise with Its Input Grounded

POWER SUPPLY

± 5V

Single 5V

NOISE (µVRMS)

360 ±10%

270 ±10%

The passband of the LTC1164-8 is from 0.995 • fCENTER to

1.005 • fCENTER. At the passband’s end points the typical

filter gain is – 3dB ±2dB relative to the gain at fCENTER.

Figure 3 shows typical passband gain variations versus

percent of frequency deviation from fCENTER. Outside the

filter’s passband, signal attenuation increases to – 50dB

for frequencies less than 0.96 • fCENTER and greater than

1.04 • fCENTER.

In applications where a signal is to be detected in the

presence of wideband noise, the ultraselectivity of the

LTC1164-8 can improve the output signal-to-noise ratio.

When wideband noise (white noise) appears at the input to

3

VS = ±5V

0

RIN = 340k

RF = 61.9k

–3

–6

–9

–12

–15

–18

–1.00

–0.50 fCENTER 0.50

1.00

PERCENT DEVIATION FROM fCENTER (±% fCENTER)

LTC1164-8 • F03

Figure 3. Typical Passband Variations

the filter, only a small amount of input noise will reach the

filter’s output. If the output noise of the LTC1164-8 is

neglected, the signal-to-noise ratio at the output of the

filter divided by the signal-to-noise ratio at the input of the

filter equals:

(S/N)OUT/(S/N)IN = 20 • Log √(BW)IN/(BW)f

where,

(BW)IN = noise bandwidth at the input of the filter

(BW)f = 0.01 • fCENTER = noise equivalent filter bandwidth

Example: A small 1kHz signal is sent through a cable that

also conducts random noise. The cable bandwidth is

3.4kHz. An LTC1164-8 is used to detect the 1kHz signal.

The signal-to-noise ratio at the output of the filter is 25.3dB

larger than the signal-to-noise ratio at the input of the filter

(20 • Log√(BW)IN/(BW)f = 20 • Log√3.4kHz/ 0.01 • 1kHz

1kHz = 25.3dB).

The AC output swing with ±5V supplies is ±4V, with a

single 5V supply it is 1V to 4V, when AGND (Pins 3, 5) is

biased at 2.5V. Table 4 lists op amps that are recom-

mended for use with an LTC1164-8. The LTC1164-8 is

designed and specified for a dual ±5V or single 5V supply

operation. The filter’s passband gain linearity is optimum

at single 5V supply and with Pins 3, 5 (AGND) biased at 2V.

Filter operation at ±7.5V supplies is not tested or speci-

fied. At VS = 7.5V, the filter will operate with center

frequencies up to 7kHz. Please refer to the Passband

Variations vs Power Supply graph in the Typical Perfor-

mance Characteristics.

7

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