Datasheet

MAX9626/MAX9627/MAX9628
Low-Noise, Low-Distortion,
1.35GHz Fully Differential Amplifiers
16
The gain options with the internal termination resistors R
T
are given by the following equation and typical numbers
are summarized in Table 2. Gain values are dependent
on actual source impedance and on-chip R
T
, R
G
, and R
F
values. The latter are subject to process variation.
( )
F T
T S G S G
R x R
GAIN
R R R R x R
=
× + +
For single-ended to differential applications where the
source impedance is 50I, such as the case of the
Typical Application Circuit, connect an external 50I
resistor at the other input to maintain symmetry and mini-
mize the gain error.
Applications Information
Input Voltage Range
One of the typical applications is the translation of a
single-ended input signal that is referenced to ground
to a differential output signal that feeds a high-speed
pipeline analog-to-digital converter (ADC) such as the
one in the Typical Application Circuit. Because the input
signal has 0V common mode, the majority of the ampli-
fiers would require a negative supply. The ICs allow the
input signal to be below ground even with single-supply
operation (V
EE
connected to GND). How far below
ground depends on the gain option. See the Electrical
Characteristics table and Figures 1, 2, and 3 for details.
Use the following equation to determine the input com-
mon-mode range:
AMP OUT_CM
IN_CM
(V V )
(G 1)
V x
(G 1) G
−
+
=
+
where V
IN_CM
is the input common-mode voltage. V
AMP
is the voltage at the input node of the internal amplifier.
V
OUT_CM
is the output common-mode voltage. G is the
gain of the device.
Table 2. Typical Gain Values When Using
the Internal Termination Resistors
(R
T
and R
S
= 50)
Figure 1. MAX9626 Input Common-Mode Voltage vs. Output
Common-Mode Voltage of the Amplifier
Figure 2. MAX9627 Input Common-Mode Voltage vs. Output
Common-Mode Voltage of the Amplifier
Figure 3. MAX9628 Input Common-Mode Voltage vs. Output
Common-Mode Voltage of the Amplifier
V
OUT_CM
(V)
V
IN_CM
(V)
2.2
2.11.9
2.0
1.3
1.4
1.5
1.6
1.7
1.8
1.1
1.2
-2.0
-1.5
-1.0
-0.5
0
0.5
1.0
1.5
2.0
2.5
-2.5
1.0
2.3
V
IN_CM
HIGH
V
IN_CM
LOW
GAIN = 1
-1.0
-0.5
0
0.5
1.0
1.5
2.0
-1.5
V
OUT_CM
(V)
V
IN_CM
(V)
2.2
2.11.9
2.0
1.3
1.4
1.5
1.6
1.7
1.8
1.1
1.21.0
2.3
V
IN_CM
HIGH
V
IN_CM
LOW
GAIN = 2
-1.0
-0.5
0
0.5
1.0
1.5
2.0
V
OUT_CM
(V)
V
IN_CM
(V)
2.2
2.11.9
2.0
1.3
1.4
1.5
1.6
1.7
1.8
1.1
1.21.0
2.3
V
IN_CM
HIGH
V
IN_CM
LOW
GAIN = 4
R
T
(I) R
G
(I) R
F
(I)
GAIN (V/V)
64 200 200 0.48
64 150 300 0.95
64 125 500 1.85