Evaluates: MAX4383
MAX4383 Evaluation Kit
_______________________________________________________________________________________ 3
Detailed Description
The MAX4383 EV kit is a fully assembled and tested
surface-mount circuit board that demonstrates the
capability of the high-speed MAX4383 op amp config-
ured in a 5-pole, active lowpass multiple feedback filter
circuit. The filter can be used for video anti-aliasing or
as a reconstruction filter for ATSC (HDTV) or high-reso-
lution (XGA) graphics. The circuit has a 75ΩDAC load
(R16), a gain of 2V/V, and a 75Ωsource (R15) for dri-
ving a 75Ωback-terminated load to an overall gain of 1.
The board operates from either a +5V single supply or
±5V dual supplies.
The MAX4383 EV kit demonstrates a lower cost, but
more accurate way to design video filters. Using R-C,
rather than L-C components, it provides a 30MHz, -3dB
bandwidth with >40dB rejection at 74.25MHz (Figure 1),
as well as group-delay compensation and buffering
using a single MAX4383 quad op amp. The improved
tolerance of R-C, versus L-C components, removes the
need for production tuning. Some initial tuning may be
required to account for the variation in the DAC load
and parasitic components due to PC board layout differ-
ences. The MAX4383 EV kit uses dual supplies, but the
MAX4383 can be run from a single supply.
The MAX4383 EV kit is a Rauch, or multiple feedback
realization of a 5-pole modified Legendre characteristic
using one 1st-order +6dB gain stage and two 2nd-order
unity-gain stages. The final stage is a 1st-order group
delay compensator, which drives the back-terminated
75Ωload to an overall unity gain. There are three sensi-
tive points in the circuit; R14, which controls the real
pole, C1 and C4, that control the high-frequency poles,
and C5 that sets the group delay compensation.
The MAX4383 EV kit comes with a 75Ωtermination (R16)
and a BNC connector (INPUT) in place of the DAC nor-
mally found at the input for measurement purposes, and
this reduces the gain to -6dB overall. The values of R14
and R16 are based on the DAC with a typical load resis-
tance of 25Ωto 35Ω. To accommodate different load
resistors, adjust the value of the R14 and the C6 product
accordingly. The values of C1 and C4 reflect a two-sided
PC board with minimal ground plane around the op
amps pins. C5 adjusts the group delay compensation.
Adjust the value of C1 and C4 for bandwidth before
adjusting C5 for group-delay variation compensation.
GAIN vs. FREQUENCY