MAX4104/MAX4105/MAX4304/MAX4305
where:
in = input current noise density (in pA/√Hz)
en = input voltage noise density (in nV/√Hz)
The MAX4104/MAX4105/MAX4304/MAX4305 have a
very low, 2.1nV/
√Hz input voltage noise density and
3.1pA/
√Hz input current noise density.
An example of DC-error calculations, using the
MAX4304 typical data and the typical operating circuit
with RF = RG = 330 (RF || RG = 165) and RS = 50
gives:
Calculating total output noise in a similar manner yields
the following:
With a 200MHz system bandwidth, this calculates to
60.8VRMS (approximately 365Vp-p, using the six-
sigma calculation).
ADC Input Buffers
Input buffer amplifiers can be a source of significant
error in high-speed ADC applications. The input buffer
is usually required to rapidly charge and discharge the
ADC’s input, which is often capacitive. In addition, the
input impedance of a high-speed ADC often changes
very rapidly during the conversion cycle—a condition
that demands an amplifier with very low output imped-
ance at high frequencies to maintain measurement
accuracy. The combination of high-speed, fast slew
rate, low noise, and low-distortion available in the
MAX4104/MAX4105/MAX4304/MAX4305 makes them
ideally suited for use as buffer amplifiers in high-speed
ADC applications.
Video Line Driver
The MAX4104/MAX4105/MAX4304/MAX4305 are opti-
mized to drive coaxial transmission lines when the
cable is terminated at both ends, as shown in Figure 2.
To minimize reflections and maximize power transfer,
select the termination resistors to match the character-
istic impedance of the transmission line. Cable frequen-
cy response can cause variations in the flatness of the
signal.
Driving Capacitive Loads
The MAX4104/MAX4105/MAX4304/MAX4305 provide
maximum AC performance when driving no output load
capacitance. This is the case when driving a correctly
terminated transmission line (i.e., a back-terminated
cable).
In most amplifier circuits, driving a large load capaci-
tance increases the chance of oscillations occurring.
The amplifier’s output impedance and the load capaci-
tor combine to add a pole and excess phase to the
loop response. If the pole’s frequency is low enough
and phase margin is degraded sufficiently, oscillations
may result.
A second concern when driving capacitive loads origi-
nates from the amplifier’s output impedance, which
e
x
e
nV Hz
n OUT
(
)
(
)
.
=
+
[ ]
+
+
=
1 1
3 1
10
50
3 1
10
165
2 1
10
4 3
12
2
12
2
9
2
V
32 x 10
50
32 x 10
165
1 x 10
1
V
15.8mV
OUT
6
3
OUT
=
( ) +
(
)+
+
[
]
=
740MHz, Low-Noise, Low-Distortion
Op Amps in SOT23-5
10
______________________________________________________________________________________
MAX4104
MAX4105
MAX4304
MAX4305
RG
FB
IB-
IB+
IN
VOUT
OUT
RS
RF
Figure 1. Output Offset Voltage
Figure 2. Video Line Driver
MAX4104
MAX4105
MAX4304
MAX4305
RG
IN-
IN+
OUT
RL
75
RT
75
RT
75
75
CABLE
75
CABLE
RF