Bandpass Filter for 1.6 MHz

Hallo

To clean up the outputs of a DDS I am looking for a bandpass filter with the
following properties:
+ Center frequency 200 kHz to 1600 kHz, fixed
+ 3-dB bandwidth 100 kHz
+ Voltage gain 1
+ Max. signal level 2 V pp
+ Slopes 20 dB/dec

There will be multiple DDS, each producing a different frequency in the
range from 200 to 1600 kHz. Each DDS may sweep by +- 50 kHz around its
nominal frequency. The filters should reduce noise, harmonics, and aliases
from the DDS output signals.

Filters should be simple to construct and tune. The effects of component
value tolerances on the center frequency must be compensated somehow,
preferably by adjustment of one resistor.

I tried to use a multi-feedback (MFB) opamp bandpass filter topology. See
here for a schematic and dimensioning:
http://sound.westhost.com/project63.htm . I tried with R1 = 12 k, R2 = 62,
R3 = 24 k, C1 = C2 = 82 p. What I like about this circuit is that its center
frequency can be adjusted by just changing R2, without affecting bandwidth
or gain. What I don't like is that the voltage divider R1 - R2 heavily
attenuates the input signal, resulting in an extremely noisy output signal.
It amplifies the opamp noise voltage by a factor of several hundred!

My questions: What circuit should I use here? Active opamp or LC, which
topology? Which opamp?

Regards,
Hans


.

Relevant Pages

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