Applications information – Rainbow Electronics MAX4029 User Manual
Page 9
The MAX4028/MAX4029 have a fixed gain of +2V/V that
is internally set with two 1k
Ω thin-film resistors. The
impedance of the internal feedback resistors must be
taken into account when operating multiple MAX4028/
MAX4029s in large multiplexer applications.
Applications Information
Video Line Driver
The MAX4028/MAX4029 are well suited to drive coaxial
transmission lines when the cable is terminated at both
ends, as shown in
Figure 3, where the fixed gain of
+2V/V compensates for the loss in the resistors, R
T
.
Driving Capacitive Loads
A correctly terminated transmission line is purely resis-
tive and presents no capacitive load to the amplifier.
Reactive loads decrease phase margin and may pro-
duce excessive ringing and oscillation.
Another concern when driving capacitive loads is the
amplifier’s output impedance, which appears inductive
at high frequencies. This inductance forms an L-C reso-
nant circuit with the capacitive load, which causes
peaking in the frequency response and degrades the
amplifier’s phase margin.
MAX4028/MAX4029
Triple/Quad, 2:1 Video
Multiplexer-Amplifiers with Input Clamps
_______________________________________________________________________________________
9
Table 2. MAX4029 Clamp Settings for Video Formats
INPUT
FORMAT
CLAMP/KEY
1
Cvbs1
Clamp
2
Cvbs2
Clamp
3
Cvbs3
Clamp
4
Cvbs4
Clamp
Gs, B, R have sync only on Green.
INPUT
FORMAT
CLAMP/KEY
1
H-Sync
Clamp
2
G
Key
3
B
Key
4
R
Key
R, G, B have sync on none.
INPUT
FORMAT
CLAMP/KEY
1
Y
Clamp
2
C
Key
3
Cvbs
Clamp
4
Cvbs
Clamp
R, G, B have sync on all.
R
T
75
Ω
R
T
75
Ω
R
T
75
Ω
OUT_
IN_A
IN_B
A/B
DISABLE
0.1
µF
75
Ω CABLE
75
Ω CABLE
R
T
75
Ω
0.1
µF
75
Ω CABLE
R
KEYREF
MAX4028
MAX4029
CLAMP
Figure 3. Video Line Driver
INPUT
FORMAT
CLAMP/KEY
1
Gs
Clamp
2
R
Key
3
B
Key
4
Cvbs
Clamp
INPUT
FORMAT
CLAMP/KEY
1
Y
Clamp
2
Pr
Key
3
Pb
Key
4
Cvbs
Clamp
INPUT
FORMAT
CLAMP/KEY
1
Cvbs
Clamp
2
G’
Clamp
3
B’
Clamp
4
R’
Clamp