19-0315; Rev 0; 10/94
950MHz FET-Input Buffer with 75
Ω
Output
_______________General Description
The MAX4005 is a ±5V, single-ended unity-gain buffer
with a high-impedance JFET input, intended to drive a
75Ω load. A 75Ω thin-film output resistor is included on-
board to minimize reflections when driving a 75Ω load
through a transmission line of arbitrary length. Gain in
this configuration is 0.5.
____________________________Features
o
950MHz Bandwidth
o
350ps Rise/Fall Times
o
0.11%/0.03° Differential Gain/Phase Error
o
1000V/µs Slew Rate
o
10pA Input Bias Current
o
75Ω Output Impedance
MAX4005
________________________Applications
Video Buffer / Line Driver
Isolation Between High-Impedance Node
and Low-Impedance Instrument
Remote Signal Sensing
Impedance Transformation
Fanout Multiplier for 75Ω Distribution Systems
______________Ordering Information
PART
MAX4005CSA
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 SO
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
-5V
1
8
-5V
V
EE
1
8
7
V
EE
PEAK
OUT
V
CCO
MAX4005
INPUT
2
3
4
7
6
5
N.C.
Z = 75Ω
+5V
OUT
R
L
= 75Ω
IN 2
GND 3
V
CC
4
MAX4005
6
5
+5V
SO
________________________________________________________________
Maxim Integrated Products
1
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950MHz FET-Input Buffer with 75
Ω
Output
MAX4005
ABSOLUTE MAXIMUM RATINGS
Input Voltage.......................................................................±2.5V
V
CC
Supply Voltage ............................................................+5.5V
Output-Stage Supply .........................................................+5.5V
V
EE
Supply Voltage..............................................................-5.5V
Peaking Pad Voltage.............................................................0.0V
Ground Voltage .....................................................................0.0V
Continuous Power Dissipation (T
A
= +70°C) ...................471mW
Operating Temperature Range...............................0°C to +70°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= 4.75V to 5.25V, V
EE
= -4.75V to -5.25V, T
A
= +25°C, stated performance characterized for T
A
= 0°C to +70°C, unless
otherwise noted.)
PARAMETER
+5V V
CC
Current
+5V Output Stage Quiescent Current
-5V V
EE
Current
Output Offset Voltage
Output Resistance
Input Current
Gain
Linearity
Input Dynamic Range
+5V V
CC
Power-Supply Rejection Ratio
+5V Output Stage Power-Supply
Rejection Ratio
-5V V
EE
Power-Supply Rejection Ratio
R
OUT
I
B
V
IN
= 0V
R
L
= 75Ω
R
L
= 75Ω, measured over input
dynamic range
R
L
= 75Ω, gain = 0.5
V
IN
= 0V, R
L
= 75Ω
V
IN
= 0V, R
L
= 75Ω
V
IN
= 0V, R
L
= 75Ω
-3dB
-6dB
V
IN
= 0.25V step, V
OUT
= 0.125V step
At 30MHz
-1.3
40
50
40
SYMBOL
I
VCC1
I
VCC2
I
VEE
CONDITIONS
V
IN
= 0V, R
L
= 75Ω
V
IN
= 0V, R
L
= 75Ω
V
IN
= 0V, R
L
= 75Ω
R
L
= 75Ω, gain = 0.5
MIN
9
9
17
-3
74.0
-1
0.49
75.0
0.01
0.50
0.50
TYP
14
11
24
MAX
19
14
31
3
76.5
1
0.51
1
1.6
55
75
60
950
2000
2.2
2
350
±0.01
60
80
V
IN
= 2.5V step with 200ps rise time
V
IN
= 2.5V step
At 50MHz
At 50MHz
At 100MHz
At 3.58MHz
At 3.58MHz
1000
5
-50
< -60
28
0.11
0.03
%
V
dB
dB
dB
UNITS
mA
mA
mA
mV
Ω
nA
TYPICAL OPERATING PERFORMANCE
(V
CC
= 5.0V, V
EE
= -5.0V, R
L
= 75Ω, T
A
= +25°C, unless otherwise noted.)
Bandwidth
Input Capacitance
Settling Time to 0.1%
Rise/Fall Times
Gain Flatness
Gain Flatness ±0.1dB
Gain Flatness ±0.2dB
Slew Rate
Overdrive Recovery Time
2nd Harmonic Distortion
3rd Harmonic Distortion
3rd-Order Intercept
Differential Gain Error
Differential Phase Error
BW
C
IN
t
SET
GF
GF1
GF2
SR
t
OD
2HD
3HD
TOI
DG
DP
t
RISE
/t
FALL
V
IN
= 0.25V step with < 30ps rise time
MHz
pF
ns
ps
dB
MHz
MHz
V/µs
ns
dBc
dBc
dBm
%
degrees
2
_______________________________________________________________________________________
950MHz FET-Input Buffer with 75
Ω
Output
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
SMALL-SIGNAL STEP RESPONSE
MAX4005-01
MAX4005-02
MAX4005
GAIN vs. FREQUENCY
-3dB, 977MHz
-6dB
VOLTAGE GAIN (5dB/div)
SMALL-SIGNAL STEP RESPONSE
MAX4005-03
OUTPUT VOLTAGE (10mV/div)
t
RISE
= 340ps
OUTPUT VOLTAGE (20mV/div)
t
RISE
= 357ps
0.3 1
10
100
1000
TIME (2ns/div)
TIME (2ns/div)
FREQUENCY (kHz)
SMALL-SIGNAL STEP RESPONSE
vs. CAPACITIVE LOAD
MAX4005-04
THIRD-ORDER INTERCEPT
vs. FREQUENCY
THIRD-ORDER INTERCEPT (dBm)
35
30
25
20
15
10
5
0
MAX4005-05
40
OUTPUT VOLTAGE (20mV/div)
C
L
= 5.6pF
C
L
= 10pF
C
L
= 18pF
C
L
= 33pF
V
IN
= 200mV STEP
R
L
= 75Ω
TIME (2ns/div)
100
150
200
250
300
350
400
FREQUENCY (MHz)
_______________________________________________________________________________________
3
950MHz FET-Input Buffer with 75
Ω
Output
MAX4005
_____________________Pin Description
PIN
1, 8
2
3
4
5
6
7
NAME
V
EE
IN
GND
V
CC
V
CCO
OUT
PEAK
FUNCTION
-5V Negative Supplies
High-Impedance Input
Ground
+5V Positive Supply
Output Stage +5V Positive Supply
Output (Z
OUT
= 75Ω)
Normally no connection. Capacitor to
ground will peak frequency response.
Input Impedance
The MAX4005 has a JFET input with an input capaci-
tance of only 2pF. As a result, the leakage current is
typically less than 10pA. This exceptionally high input
impedance is important in applications that require iso-
lation between a high source impedance and a low-
impedance transmission cable. An attenuator may be
used in front of the MAX4005 to increase the dynamic
range and reduce input capacitance.
Output Impedance
A 75Ω precision thin-film output resistor is included on-
board to provide more precise reverse termination
than standard discrete resistors. This minimizes reflec-
tions caused by impedance mismatching when driving
transmission cable. The MAX4005 can also drive a
50Ω load with only a slight loss in amplitude (gain
drops from 0.5 to 0.4). The typical operating perfor-
mance specifications shown in the
Electrical
Characteristics
have been verified with a 50Ω load, as
well as a 75Ω load.
__________Applications Information
Power Supply
The MAX4005 allows for two separate +5V supplies for
the output stage and the rest of the MAX4005 circuit. The
supplies are bonded out separately to give the option of
using a different +5V supply. The output stage is a Class
A type, with the output transistor fed by a current source
in the emitter, so its current will vary with output signal.
For best bandwidth and pulse response, solder bypass
chip capacitors directly from the supply pins on the four
corners of the package to a ground plane.
Frequency Response Peaking
To peak the response to compensate for losses when
driving long transmission lines, connect a chip capaci-
tor of about 10pF to 50pF between the PEAK pin and
ground. This peaking occurs in the 200MHz to 500MHz
range. The PEAK pin will normally be left open for flat-
test response.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
4
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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