High Frequency Active Antialiasing Filters – Design Note 313
Philip Karantzalis
Introduction
High frequency (1MHz or higher) active lowpass filters
are now practical alternatives to passive LC filters mainly
due to the availability of very high bandwidth (100MHz or
higher) integrated amplifiers. Analog signal filtering applications with bandwidths in the megahertz region can
be implemented by a discrete active filter circuit using
resistors, capacitors and a 400MHz operational amplifier
such as the LTВ®1819 or the LT6600-10, a fully integrated
lowpass filter. The LT6600-10 has a fixed 10MHz frequency
response equivalent to a fourth order flat passband Chebyshev function. An LT1819-based active RC lowpass
filter can be designed to have a Chebyshev, Butterworth,
Bessel or custom frequency response (up to 20MHz).
The LT6600-10 Lowpass Filter
The LT6600-10 is a fully integrated, differential, fourth
order lowpass filter in a surface mount SO-8 package
(Figure 1). Two external resistors ranging from 1600О© to
100Ω set the differential gain in the filter’s passband from
–12dB to 12dB, respectively. The LT6600-10 passband
gain ripple is a maximum of 0.7dB to –0.3dB up to 10MHz
and attenuation is typically 28dB at 30MHz and 44dB at
50MHz. The signal to noise ratio (SNR) at the filter’s output …