ada4938-2 Analog Devices, Inc., ada4938-2 Datasheet - Page 21

• Manufacturer Part Number: ada4938-2
• Description: Ultralow Distortion Differential Adc Driver
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
SETTING THE OUTPUT COMMON-MODE VOLTAGE
The V
approximately equal to the midsupply point (average value of
the voltages on V+ and V−). Relying on this internal bias results
in an output common-mode voltage that is within about 100 mV of
the expected value.
In cases where more accurate control of the output common-
mode level is required, it is recommended that an external
source, or resistor divider (10 kΩ or greater resistors), be used.
Table 9. Differential Ground-Referenced Input, DC-Coupled; See Figure 56
Nominal
Gain (dB)
0
3
6
10
12
14
Table 10. Single-Ended Ground-Referenced Input, DC-Coupled, R
Nominal
Gain (dB)
0
3
6
10
12
14
1
R
G2
= R
OCM
G1
+ (R
pin of the ADA4938 is internally biased at a voltage
S
||R
R
200
348
280
348
200
348
316
348
402
348
499
348
R
(Ω)
200
348
280
348
200
348
316
348
402
348
499
348
F
F
T
)
(Ω)
R
(Ω)
200
348
200
249
100
174
100
110
100
86.6
100
69.8
G1
R
200
348
200
249
100
174
100
110
100
86.6
100
69.8
G
(Ω)
R
(Ω)
61.9
56.2
60.4
59.0
75.0
61.9
73.2
69.8
71.5
76.8
71.5
86.6
T
R
(Ω)
400
696
400
498
200
348
200
220
200
173
200
140
IN, dm
R
(Ω)
267
464
282
351
150
261
161
177
167
144
171
120
IN,se
R
(Ω)
226
374
226
274
130
200
130
140
130
118
130
100
Differential
Output
Noise Density
(nV/√Hz)
5.8
6.7
7.2
7.6
8.0
9.0
11
12
14
13
17
16
G2
1
Differential
Output
Noise
Density
(nV/√Hz)
5.5
6.5
6.8
7.3
7.0
8.4
9.7
10
12
11
14
12
Approximate
Large-Signal
Bandwidth (MHz)
Rev. PrB | Page 21 of 23
Approximate
Large-Signal
Bandwidth
(MHz)
750
500
270
160
S
= 50 Ω; See Figure 57
It is also possible to connect the V
level (CML) output of an ADC. However, care must be taken to
assure that the output has sufficient drive capability. The input
impedance of the V
ADA4938 devices share one reference output, it is
recommended that a buffer be used.
Table 9 and Table 10 list several common gain settings,
associated resistor values, input impedance, output noise
density, and approximate large signal bandwidth for both balanced
and unbalanced input configurations. Also shown are the input
common-mode voltage swings under the given conditions for
different V
V
0
0
0
0
0
0
V
−0.56 to +0.56
−0.40 to +0.40
−0.33 to +0.33
−0.21 to +0.21
−0.16 to +0.16
−0.13 to +0.13
OCM
OCM
+V
+V
OCM
= 0 V
= 0 V
V
V
OUT, dm
OUT,dm
S
S
= 5 V, -V
settings with both dual and single 5 V supplies.
= 5 V, -V
Common-Mode Level at +IN, −IN (V)
Common-Mode Swing at +IN, -IN (V)
= 2.0 V p-p
= 2.0 V p-p
OCM
S
S
V
1.75
1.46
1.17
0.84
0.70
0.58
V
1.29 to 2.42
1.16 to 1.97
1.05 to 1.70
0.82 to 1.23
0.70 to 1.02
0.59 to 0.85
pin is approximately 10 kΩ. If multiple
= −5 V
= −5 V
OCM
OCM
= 3.5 V
= 3.5 V
OCM
V
1.25
1.04
0.83
0.60
0.50
0.42
V
0.75 to 1.75
0.71 to 1.52
0.66 to 1.31
0.52 to 0.93
0.45 to 0.77
0.39 to 0.65
input to a common-mode
OCM
OCM
V
V
= 2.5 V
= 2.5 V
OUT, dm
OUT, dm
ADA4938-2
+V
+V
= 2.0 V p-p
= 2.0 V p-p
S
S
= 5 V
= 5 V
V
1.60
1.33
1.07
0.77
0.64
0.53
V
1.13 to 2.26
1.03 to 1.83
0.94 to 1.59
0.73 to 1.14
0.62 to 0.94
0.53 to 0.79
OCM
OCM
= 3.2 V
= 3.2 V