MAX7490-MAX7491 查看數據表（PDF） - Maxim Integrated
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MAX7490-MAX7491 Datasheet PDF : 18 Pages
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Dual Universal Switched-Capacitor Filters
Table 1. Filter Operating Modes
MODE LP
HP
BP
N
LP-N* HP-N*
COMMENTS
1
•
•
•
fCLK/fO ratio is the nominal value. Good for bandpass filters
with identical sections cascaded, higher order Butterworth filters,
high-Q bandpass, low-Q notches.
1B
•
•
•
Same as Mode 1 with fCLK/fO ratios greater than the nominal
value.
2
•
•
•
Combination of Mode 1 and Mode 3; fCLK/fO ratios always
less than the nominal value. Less sensitivity to resistor tolerances
than Mode 3.
Extension of Mode 2 that allows higher frequencies. Highpass
2N
•
and lowpass outputs are summed with external op amp and
two resistors. Good for lowpass elliptic filters.
3
•
•
•
Adjustable fO above and below the nominal frequency.
Commonly used for multiple-pole Chebyshev filters, all-pole
higher order bandpass, lowpass, and highpass filters.
3A
•
•
•
Extension of Mode 3 that needs an external op amp and
•
•
two additional resistors. Commonly used for lowpass or higher
elliptic or Cauer filters.
*LP-N = lowpass notch, HP-N = highpass notch. Both require an external op amp. See Definition of Terms (Table 2).
Table 2. Definition of Terms
TERM
fCLK
fO
fNOTCH
Q
HOBP
HOLP
HOHP
HON1
HON2
LP-N
HP-N
DEFINITION
The clock frequency applied to the switched-capacitor filter.
The center frequency of the 2nd-order complex pole pair, fO, is determined by measuring the peak response
frequency at the bandpass output.
The frequency of minimum amplitude response at the notch output.
Quality factor, or Q, is the ratio of fO to the -3dB bandwidth of the 2nd-order bandpass filter. Q also determines
the amount of amplitude peaking at the lowpass and highpass outputs, but is not measured at these outputs.
The gain in V/V of the bandpass output at f = fO.
The gain in V/V of the lowpass output at f→0Hz.
The gain in V/V of the highpass output at f→fCLK/2.
The notch output gain as f→0Hz.
The notch output gain at f = fCLK/2.
A notch output with HON1 > HON2.
A notch output with HON1 < HON2.
10 ______________________________________________________________________________________
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