MAX9504A/MAX9504B
3V/5V, 6dB Video Amplifiers with
High Output-Current Capability
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3rd-Order Butterworth Lowpass Filter Realization
If a flatter passband and more stopband attenuation
are desired, a 3rd-order lowpass filter can be used.
The design procedures are similar to the 2nd-order
Butterworth lowpass filter.
Table 3 shows the normalized 3rd-order Butterworth
lowpass filter with the cutoff frequency at 1 rad/s and
the stopband frequency at 3 rad/s. Table 4 shows the
appropriate L and C values for different source/load
impedances, the bench measurement values for the -3dB
frequency and the attenuation at 27MHz. The attenua-
tion is over 40dB at 27MHz. At 6MHz, the attenuation is
approximately 0.6dB for R1 = R2 = 150Ω (Figure 6).
Y/C-to-Composite Mixer and Driver Circuit
The Y/C-to-composite mixer and driver use two low-
pass filters, the MAX9504A and the MAX9504B. In
Figure 7, the top video DAC generates a luma signal,
which is filtered through the passive RLC network and
then amplified by the MAX9504B. The bottom video
DAC generates a chroma signal, which is filtered and
then amplified by the MAX9504A.
LUMA OUT is directly connected to the output of the
MAX9504B through a 75Ω back-termination resistor;
likewise, CHROMA OUT to the output of the MAX9504A.
CVBS OUT (the composite video with blanking and
sync output) is created by AC-coupling the chroma sig-
nal to the luma signal through the 470pF capacitor,
which looks like an AC short at the color subcarrier fre-
quency of 3.58MHz for NTSC or 4.43MHz for PAL.
This circuit relies upon the feature that the MAX9504A/
MAX9504B can drive two loads at the same time.
Table 4. Bench Measurement Values—3rd Order LPF
