8th-Order, Lowpass,

Switched-Capacitor Filters

8

_______________________________________________________________________________________

order continuous lowpass filter. This filter is convenient for

anti-aliasing applications, or for clock noise attenuation at

the switched-capacitor filter’s output. Figure 4 shows a

2nd-order lowpass Butterworth filter built using the

uncommitted op amp with a 10kHz corner frequency.

This filter’s input resistance of 22k satisfies the minimum

load requirements of the switched-capacitor filter.

The uncommitted op amp (with a 2MHz gain bandwidth

product) can alternatively be used at the input of the

switched-capacitor filter to help reduce any possible

clock ripple feedthrough to the output.

DAC Post-Filtering

When using the MAX291/MAX292/MAX295/MAX296 for

DAC post-filtering, synchronize the DAC and the filter

clocks. If clocks are not synchronized, beat frequen-

cies will alias into the desired passband. The DAC’s

clock should be generated by dividing down the

switched-capacitor filter’s clock.

Harmonic Distortion

Harmonic distortion arises from nonlinearities within the

filters. These nonlinearities generate harmonics when a

pure sine wave is applied to the filter input. Table 2 lists

typical harmonic distortion values for the MAX291/

MAX292/MAX295/MAX296 with a 1kHz 5Vp-p sine-wave

input signal, a 1 MHz clock frequency, and a 5k

Ω load.

MAX29_

4

C1

330pF

3

INPUT

C2

1500pF

22k

R1

22k

R2

22k

R3

OUTPUT

OP OUT

OP IN

Figure 4. Uncommitted Op Amp Configured as a 2nd-Order

Table 2. Typical Harmonic Distortion (dB)

-96

-92

-82

-83

-96

-97

-88

-89

-71

-93

-71

-72

-89

-86

-82

-78

4th

5th

2nd

3rd

Filter

Harmonic

MAX296

MAX295

MAX292

MAX291

_Ordering Information (continued)

* Contact factory for dice specifications.

** Contact factory for availability and processing to MIL-STD-883.

Pin Configuration is 8-pin DIP/SO.

8 CERDIP**

-55°C to +125°C

MAX296MJA

16 Wide SO

8 Plastic DIP

Dice*

0°C to +70°C

-40°C to +85°C

-40°C to +85°C

MAX296EWE

16 Wide SO

0°C to +70°C

MAX296EPA

MAX296C/D

MAX296CWE

8 Plastic DIP

8 CERDIP**

16 Wide SO

-40°C to +85°C

-55°C to +125°C

0°C to +70°C

MAX296CPA

MAX295MJA

MAX295EWE

8 Plastic DIP

-40°C to +85°C

MAX295EPA

Dice*

16 Wide SO

0°C to +70°C

0°C to +70°C

MAX295C/D

8 Plastic DIP

0°C to +70°C

MAX295CWE

MAX295CPA

8 CERDIP**

-55°C to +125°C

MAX292MJA

16 Wide SO

8 Plastic DIP

Dice*

0°C to +70°C

-40°C to +85°C

-40°C to +85°C

MAX292EWE

16 Wide SO

0°C to +70°C

MAX292EPA

MAX292C/D

MAX292CWE

PIN-PACKAGE

TEMP. RANGE

PART

8 Plastic DIP

0°C to +70°C

MAX292CPA

8 SO

0°C to +70°C

MAX292CSA

8 SO

-40°C to +85°C

MAX292ESA

8 SO

0°C to +70°C

MAX295CSA

8 SO

-40°C to +85°C

MAX295ESA

8 SO

0°C to +70°C

MAX296CSA

8 SO

-40°C to +85°C

MAX296ESA