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

50

Ω impedance path. It is terminated by a 50Ω chip

resistor.

Bypass Components—Capacitors

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.

Creating Large Arrays

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 20

Ω. 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:

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.

1

2

N

3pF

C

20

MHz

STRAY

π×

×

+

330MHz, 4x1 Precision Video Multiplexer

_______________________________________________________________________________________

7

A1

A0

EN

OUT

X

X

0

High-Z

0

0

1

IN0

0

1

1

IN1

1

0

1

IN2

1

1

1

IN3

Table 1. Truth Table