MAX7490 Maxim, MAX7490 Datasheet - Page 10

• Manufacturer Part Number: MAX7490
• Description: Dual Universal Switched-Capacitor Filters
• Manufacturer: Maxim

Dual Universal Switched-Capacitor Filters
10
Table 1. Filter Operating Modes
Table 2. Definition of Terms
* LP-N = lowpass notch, HP-N = highpass notch. Both require an external op amp. See Definition of Terms (Table 2).
MODE
1B
2N
3A
1
2
3
f
TERM
NOTCH
______________________________________________________________________________________
H
H
H
H
H
HP-N
LP-N
f
CLK
OHP
f
OBP
OLP
ON1
ON2
Q
O
LP
•
•
•
•
•
The clock frequency applied to the switched-capacitor filter.
The center frequency of the 2nd-order complex pole pair, f
frequency at the bandpass output.
The frequency of minimum amplitude response at the notch output.
Quality factor, or Q, is the ratio of f
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 = f
The gain in V/V of the lowpass output at f→0Hz.
The gain in V/V of the highpass output at f→f
The notch output gain as f→0Hz.
The notch output gain at f = f
A notch output with H
A notch output with H
HP
•
•
BP
•
•
•
•
•
ON1
ON1
N
•
•
•
> H
< H
CLK
L P- N *
ON2.
ON2.
•
•
/2.
O
to the -3dB bandwidth of the 2nd-order bandpass filter. Q also determines
H P- N *
•
CLK
O
.
f
with identical sections cascaded, higher order Butterworth filters,
high-Q bandpass, low-Q notches.
Same as Mode 1 with f
value.
Combination of Mode 1 and Mode 3; f
less than the nominal value. Less sensitivity to resistor tolerances
than Mode 3.
Extension of Mode 2 that allows higher frequencies. Highpass
and lowpass outputs are summed with external op amp and
two resistors. Good for lowpass elliptic filters.
Adjustable f
Commonly used for multiple-pole Chebyshev filters, all-pole
higher order bandpass, lowpass, and highpass filters.
Extension of Mode 3 that needs an external op amp and
two additional resistors. Commonly used for lowpass or higher
elliptic or Cauer filters.
CLK
/2.
DEFINITION
/f
O
ratio is the nominal value. Good for bandpass filters
O
O
, is determined by measuring the peak response
above and below the nominal frequency.
CLK
COMMENTS
/f
O
ratios greater than the nominal
CLK
/f
O
ratios always