LTC1069-7 Просмотр технического описания (PDF) - Linear Technology
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LTC1069-7 Datasheet PDF : 10 Pages
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LTC1069-7
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. Most of the wideband
noise frequency contents lie within the filter 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
4.75V
±5V
CLOCK FEEDTHROUGH
125μVRMS
140μVRMS
Aliasing
Aliasing is an inherent phenomenon of sampled data
systems and it occurs for input frequencies approaching
the sampling frequency. The internal sampling frequency
of the LTC1069-7 is 50 times its fCUTOFF frequency. For
instance if a 48kHz, 100mVRMS signal is applied at the
input of an LTC1069-7 operating with a 50% duty cycle
25kHz clock, a 2kHz, 741μVRMS alias signal will appear
at the filter output. Table 4 shows details.
Table 4. Aliasing
INPUT FREQUENCY OUTPUT LEVEL
VIN = 1VRMS
Relative to Input
fCLK/fC = 25:1, fCUTOFF = 1kHz
40kHz (or 60kHz)
– 59.9dB
47kHz (or 53kHz)
– 54.2dB
48kHz (or 52kHz)
– 42.6dB
48.5kHz (or 51.5kHz)
–18.3dB
49kHz (or 52kHz)
–2.9dB
49.5kHz (or 50.5kHz)
– 0.65dB
OUTPUT FREQUENCY
Aliased Frequency
10kHz
3kHz
2kHz
1.5kHz
1.0kHz
0.5kHz
Speed Limitations
To avoid op amp slew rate limiting, the signal amplitude
should be kept below a specified level as shown in Table 5.
Table 5. Maximum VIN vs VS and Clock
VS
MAXIMUM CLOCK
MAXIMUM VIN
5V
≥ 2.5MHz
340mVRMS (fIN ≥ 200kHz)
±5V
≥ 4.5MHz
1.2VRMS (fIN ≥ 400kHz)
10697fa
8
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