LTC1069-6 データシートの表示（PDF） - Linear Technology

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LTC1069-6

Single Supply, Very Low Power, Elliptic Lowpass Filter

Linear Technology 

LTC1069-6

APPLICATIONS INFORMATION

Wideband Noise

The wideband noise of the filter is the total RMS value

of the device’s noise spectral density and determines the

operating signal-to-noise ratio. The frequency contents

of the wideband noise lie within the filter’s passband. The

wideband noise cannot be reduced by adding post filtering.

The total wideband noise is nearly independent of the

clock frequency and depends slightly on the power supply

voltage (see Table 3). The clock feedthrough specifications

are not part of the wideband noise.

Table 3. Wideband Noise

VS

3.3V

5V

±5V

WIDEBAND NOISE

118μVRMS

123μVRMS

127μVRMS

Aliasing

Aliasing is an inherent phenomenon of sampled data

systems and occurs for input frequencies approaching

the sampling frequency. The internal sampling frequency

of the LTC1069-6 is 100 times its cutoff frequency. For

instance, if a 98.5kHz, 100mVRMS signal is applied at

the input of an LTC1069-6 operating with a 50kHz clock,

a 1.5kHz, 484μVRMS alias signal will appear at the filter

output. Table 4 shows details.

Table 4. Aliasing (fCLK = 50kHz)

INPUT FREQUENCY OUTPUT LEVEL

(VIN = 1VRMS)

(kHz)

(Relative to Input)

(dB)

fCLK/fC = 50:1, fCUTOFF = 1kHz

96 (or 104)

– 78.3

97 (or 103)

–70.4

98 (or 102)

– 80.6

98.5 (or 101.5)

– 46.3

99 (or 101)

– 2.8

99.5 (or 100.5)

–1.38

OUTPUT FREQUENCY

(Aliased Frequency)

(kHz)

4.0

3.0

2.0

1.5

1.0

0.5

10696fa

8

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