MAX4141 Maxim, MAX4141 Datasheet - Page 7

• Manufacturer Part Number: MAX4141
• Description: 330MHz / 4x1 Precision Video Multiplexer
• Manufacturer: Maxim

On Maxim’s evaluation kit, the ground plane has been
removed from areas where keeping the trace capaci-
tance to a minimum is more important than maintaining
ground continuity. For example, the ground plane has
been removed from beneath the IC to minimize pin
capacitance.
The signal input line is approximately 0.103 inches
wide to minimize inductance and to provide a constant
50Ω impedance path. It is terminated by a 50Ω chip
resistor.
Electrolytic and tantalum capacitors are available from
0.1µF to over 300µF, but have resonant frequencies
below 1MHz. Ceramic capacitors are highly recom-
mended and are available to 1µF, with the smaller val-
ues having resonant frequencies to almost 1GHz. The
less expensive capacitors are constructed using a
multilayer approach; high values are available, but res-
onant frequencies beyond a few hundred megahertz
are not, because of the inductive effect of the multiple
layers. More expensive, solid dielectric microwave
porcelain/ceramic capacitors are available up to
1000pF with resonant frequencies beyond 20GHz. In all
types, resonant frequency depends on capacitor value,
voltage rating, and physical size; the larger the capaci-
tor, the lower the resonant frequency.
We recommend ceramic surface-mount/chip capaci-
tors. Placement of bypass capacitors on the PC board
is critical, and the smaller chip capacitors allow place-
ment as close to the part as practical. The smaller,
higher frequency capacitors should be placed as close
to the chip as possible, with the higher-value capaci-
tors placed farther away.
Bypass Components—Capacitors
330MHz, 4x1 Precision Video Multiplexer
_______________________________________________________________________________________
The MAX4141 was designed as a building block for
large arrays. The high-power drive required for internal
cable drivers has a negative effect on crosstalk and
increases system power consumption. Figure 1 shows
an 8x1 multiplexer circuit.
Even though the MAX4141 drives capacitive loads, you
may want to limit the number of switches connected
together to maximize bandwidth. The MAX4141 has a
finite input capacitance of about 3pF and a dynamic
output resistance of about 20Ω. This causes a pole at a
little more than 2.6GHz. However, in a large array with
many switch inputs, the total capacitance is (N x 3pF),
where “N” is the number of switches connected in par-
allel. The pole will be located at:
where C
connect.
If the maximum number of switches that may be con-
nected while still maintaining bandwidth is less than
your system requirements, use a unity-gain buffer
amplifier to isolate the switch from the remainder of the
inputs.
Table 1. Truth Table
A1
X
0
0
1
1
STRAY
2
is the stray capacitance from the inter-
N 3pF C
A0
X
0
1
0
1
1
Creating Large Arrays
STRAY
EN
0
1
1
1
1
20
MHz
High-Z
OUT
IN0
IN1
IN2
IN3
7