Detailed Description
The MAX4310/MAX4311/MAX4312 combine 2-channel,
4-channel, or 8-channel multiplexers, respectively, with
an adjustable-gain output amplifier optimized for
closed-loop gains of +1V/V (0dB) or greater. The
MAX4313/MAX4314/MAX4315 combine 2-channel, 4-
channel, or 8-channel multiplexers, respectively, with a
+2V/V (6dB) fixed-gain amplifier, optimized for driving
back-terminated cables. These devices operate from a
single supply voltage of +4V to +10.5V, or from dual
supplies of ±2V to ±5.25V. The outputs may be placed
in a high-impedance state and the supply current mini-
mized by forcing the SHDN pin low. The input multi-
plexers feature short 40ns channel-switching times and
small 10mVp-p switching transients. The input capaci-
tance remains constant at 1pF whether the channel is
on or off, providing a predictable input impedance to
the signal source. These devices feature single-supply,
rail-to-rail, voltage-feedback output amplifiers that
achieve up to 540V/µs slew rates and up to 345MHz
-3dB bandwidths. These devices also feature excellent
harmonic distortion and differential gain/phase perfor-
mance.
Applications Information
Rail-to-Rail Outputs, Ground-Sensing Input
The input common-mode range extends from the nega-
tive supply rail to V
CC
- 2.7V with excellent common-
mode rejection. Beyond this range, multiplexer
switching times may increase and the amplifier output
is a nonlinear function of the input, but does not under-
go phase reversal or latchup.
The output swings to within 250mV of V
CC
and 40mV of
V
EE
with a 10kΩ
load. With a 150Ω load to ground, the
output swings from 30mV above V
EE
to within 730mV of
the supply rail. Local feedback around the output stage
ensures low open-loop output impedance to reduce
gain sensitivity to load variations. This feedback also
produces demand-driven bias current to the output
transistors for ±95mA drive capability while constrain-
ing total supply current to only 6.1mA.
Feedback and Gain Resistor Selection
(MAX4310/MAX4311/MAX4312)
Select the MAX4310/MAX4311/MAX4312 gain-setting
feedback (R
F
) and input (R
G
) resistors to fit your applica-
tion. Large resistor values increase voltage noise and
interact with the amplifier’s input and PC board capaci-
tance. This can generate undesirable poles and zeros,
and can decrease bandwidth or cause oscillations. For
example, a noninverting gain of +2V/V configuration (R
F
=
R
G
) using 1kΩ resistors, combined with 2pF of input
capacitance and 1pF of PC board capacitance, causes a
pole at 159MHz. Since this pole is within the amplifier
bandwidth, it jeopardizes stability. Reducing the 1kΩ
resistors to 100Ω extends the pole frequency to 1.59GHz,
but could limit output swing by adding 200Ω in parallel
with the amplifier’s load resistor.
Table 1 shows suggested RF and RG values for the
MAX4310/MAX4311/MAX4312 when operating in the non-
inverting configuration (shown in Figure 1). These values
provide optimal AC response using surface-mount resis-
tors and good layout techniques, as discussed in the
Layout and Power-Supply Bypassing section.
Stray capacitance at the FB pin causes feedback resis-
tor decoupling and produces peaking in the frequency-
response curve. Keep the capacitance at FB as low as
possible by using surface-mount resistors and by
avoiding the use of a ground plane beneath or beside
these resistors and the FB pin. Some capacitance is
unavoidable; if necessary, its effects can be neutralized
by adjusting RF. Use 1% resistors to maintain consis-
tency over a wide range of production lots.
MAX4310–MAX4315
High-Speed, Low-Power, Single-Supply
Multichannel, Video Multiplexer-Amplifiers
12 ______________________________________________________________________________________
MAX4310
R
T
75Ω
8OUT
7FB
IN0
IN1
4
5
1
A0
R
T
75Ω
R
G
R
F
75Ω CABLE
R
T
75Ω
R
T
75Ω
75Ω CABLE
75Ω CABLE
(MHz)
100∝ 280 60
2 6 500
Figure 1. MAX4310 Noninverting Gain Configuration
Table 1. Bandwidth and Gain with
Suggested Gain-Setting resistors
(MAX4310/MAX4311/MAX4312)
