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MAX4305EUK-T

P1-P3P4-P6P7-P9P10-P12
MAX4104/MAX4105/MAX4304/MAX4305
where:
i
n
= input current noise density (in pA/√Hz)
e
n
= 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 R
F
= R
G
= 330Ω (R
F
|| R
G
= 165Ω) and R
S
= 50Ω
gives:
Calculating total output noise in a similar manner yields
the following:
With a 200MHz system bandwidth, this calculates to
60.8µV
RMS
(approximately 365µVp-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 x x x x
e nV Hz
n OUT
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 1
V 15.8mV
OUT
6 6 3
OUT
=
( )
+
( )
+
+
[ ]
=
− − −
Ω
740MHz, Low-Noise, Low-Distortion
Op Amps in SOT23-5
10 ______________________________________________________________________________________
MAX4104
MAX4105
MAX4304
MAX4305
R
G
FB
I
B-
I
B+
IN
V
OUT
OUT
R
S
R
F
Figure 1. Output Offset Voltage Figure 2. Video Line Driver
MAX4104
MAX4105
MAX4304
MAX4305
R
G
IN-
IN+
OUT
R
L
75Ω
R
T
75Ω
R
T
75Ω
75Ω CABLE
75Ω CABLE
R
F
appears inductive at high frequencies. This inductance
forms an L-C resonant circuit with the capacitive load,
which causes peaking in the frequency response and
degrades the amplifier’s phase margin.
The MAX4104/MAX4105/MAX4304/MAX4305 drive
capacitive loads up to 10pF without oscillation.
However, some peaking may occur in the frequency
domain (Figure 3). To drive larger capacitance loads or
to reduce ringing, add an isolation resistor between the
amplifier’s output and the load (Figure 4).
The value of R
ISO
depends on the circuit’s gain and the
capacitive load (Figure 5). Figure 6 shows the
MAX4104/MAX4105/MAX4304/MAX4305 frequency
response with the isolation resistor and a capacitive
load. With higher capacitive values, bandwidth is domi-
nated by the RC network formed by R
ISO
and C
L
; the
bandwidth of the amplifier itself is much higher. Also
note that the isolation resistor forms a divider that
decreases the voltage delivered to the load.
Maxim’s High-Speed Evaluation Boards
The MAX4104 evaluation kit manual shows a suggest-
ed layout for Maxim’s high-speed, single-amplifier eval-
uation boards. This board was developed using the
techniques described previously (
see Layout and
Power-Supply Bypassing
section). The smallest avail-
able surface-mount resistors were used for the feed-
back and back-termination resistors to minimize the
MAX4104/MAX4105/MAX4304/MAX4305
740MHz, Low-Noise, Low-Distortion
Op Amps in SOT23-5
______________________________________________________________________________________ 11
Figure 3a. MAX4104 Frequency Response with Capacitive
Load and No Isolation Resistor
30
25
-20
100k 1M 10M 100M 1G
-10
-15
FREQUENCY (Hz)
GAIN (dB)
0
-5
10
5
20
15
C
L
= 10pF
C
L
= 5pF
C
L
= 15pF
25
20
-25
100k 1M 10M 100M 1G
-15
-20
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
-5
-10
5
0
15
10
C
L
= 5pF
C
L
= 15pF
C
L
= 10pF
Figure 3b. MAX4304 Frequency Response with Capacitive
Load and No Isolation Resistor
Figure 3d. MAX4305 Frequency Response with Capacitive
Load and No Isolation Resistor
Figure 3c. MAX4105 Frequency Response with Capacitive
Load and No Isolation Resistor
30
25
-20
100k 1M 10M 100M 1G
-10
-15
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
0
-5
10
5
20
15
C
L
= 5pF
C
L
= 15pF
C
L
= 10pF
25
20
-25
100k 1M 10M 100M 1G
-15
-20
FREQUENCY (Hz)
NORMALIZED GAIN (dB)
-5
-10
5
0
15
10
C
L
= 5pF
C
L
= 15pF
C
L
= 10pF
MAX4104/MAX4105/MAX4304/MAX4305
distance from the IC to these resistors, thus reducing
the capacitance associated with longer lead lengths.
SMA connectors were used for best high-frequency
performance. Because distances are extremely short,
performance is unaffected by the fact that inputs and
outputs do not match a 50Ω line. However, in applica-
tions that require lead lengths greater than 1/4 of the
wavelength of the highest frequency of interest,
constant-impedance traces should be used.
Fully assembled evaluation boards are available for the
MAX4104 in an 8-pin SO package.
740MHz, Low-Noise, Low-Distortion
Op Amps in SOT23-5
12 ______________________________________________________________________________________
MAX4104
MAX4105
MAX4304
MAX4305
R
G
IN-
IN+
R
ISO
OUT
R
F
C
L
R
L
0
10
5
20
15
25
30
0 10050 150 200 250
CAPACITIVE LOAD (pF)
OPTIMAL ISLOATION RESISTOR (Ω)
MAX4105/MAX4305
MAX4104/MAX4304
Figure 5. Optimal Isolation Resistor (R
ISO
) vs. Capacitive
Load
4
3
-6
100k 1M 10M 100M 1G
-4
-5
FREQUENCY (Hz)
GAIN (dB)
-2
-3
0
-1
2
1
C
L
= 47pF
MAX4104/MAX4304
R
ISO
= 15Ω
C
L
= 83pF
C
L
= 68pF
Figure 6. Frequency Responses vs. Capacitive Load with 15
Ω
Isolation Resistor
Figure 4. Using an Isolation Resistor (R
ISO
) for High Capacitive
Loads
Chip Information
TRANSISTOR COUNT: 44
SUBSTRATE CONNECTED TO V
EE
Ordering Information (continued)
*
Future product—contact factory for availability.
PART
MAX4105ESA
-40°C to +85°C
TEMP. RANGE
PIN-
PACKAGE
8 SO
MAX4105EUK-T -40°C to +85°C 5 SOT23-5
MAX4304ESA
MAX4304EUK-T
MAX4305ESA*
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C 8 SO
5 SOT23-5
8 SO
MAX4305EUK-T -40°C to +85°C 5 SOT23-5
SOT
TOP MARK
—
ACCP
—
ACCQ
—
ACCR
OUT
IN+
N.C.
V
EE
1
2
8
7
N.C.
V
CC
IN-
N.C.
MAX4304
MAX4305
MAX4104
MAX4105
SO
TOP VIEW
3
4
6
5
Pin Configurations (continued)
P1-P3P4-P6P7-P9P10-P12

MAX4305EUK-T

Mfr. #:
Buy MAX4305EUK-T
Manufacturer:
Maxim Integrated
Description:
Operational Amplifiers - Op Amps 740MHz Low-Noise ow-Distortion
Lifecycle:
New from this manufacturer.
Delivery:
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