AD8138ARM Analog Devices Inc, AD8138ARM Datasheet - Page 21

IC AMP DIFF LDIST LP 95MA 8MSOP

AD8138ARM

Manufacturer Part Number
AD8138ARM
Description
IC AMP DIFF LDIST LP 95MA 8MSOP
Manufacturer
Analog Devices Inc
Type
ADC Driverr
Datasheet

Specifications of AD8138ARM

Rohs Status
RoHS non-compliant
Design Resources
DC-Coupled, Single-Ended-to-Differential Conversion Using AD8138 and AD7352 (CN0040) DC-Coupled, Single-Ended-to-Differential Conversion Using AD8138 and AD7356 (CN0041) DC-Coupled, Single-Ended-to-Differential Conversion Using AD8138 and AD7357 (CN0061)
Applications
Data Acquisition
Mounting Type
Surface Mount
Package / Case
8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
Number Of Channels
1
Number Of Elements
1
Power Supply Requirement
Single/Dual
Common Mode Rejection Ratio
70dB
Voltage Gain Db
0.028dB
Input Resistance
6@5VMohm
Input Offset Voltage
2.5@5VmV
Input Bias Current
7@5VnA
Single Supply Voltage (typ)
3/5/9V
Dual Supply Voltage (typ)
±3/±5V
Power Supply Rejection Ratio
70dB
Power Dissipation
550mW
Rail/rail I/o Type
No
Single Supply Voltage (min)
2.7V
Single Supply Voltage (max)
11V
Dual Supply Voltage (min)
±1.4V
Dual Supply Voltage (max)
±5.5V
Operating Temp Range
-40C to 85C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
8
Package Type
MSOP
Lead Free Status / RoHS Status
Not Compliant

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HIGH PERFORMANCE ADC DRIVING
The circuit in Figure 46 shows a simplified front-end
connection for an AD8138 driving an AD9224, a 12-bit,
40 MSPS ADC. The ADC works best when driven differentially,
which minimizes its distortion. The AD8138 eliminates the
need for a transformer to drive the ADC and performs single-
ended-to-differential conversion, common-mode level-shifting,
and buffering of the driving signal.
The positive and negative outputs of the AD8138 are connected
to the respective differential inputs of the
49.9 Ω resistors to minimize the effects of the switched-capacitor
front end of the AD9224. For best distortion performance, it
runs from supplies of ±5 V.
The AD8138 is configured with unity gain for a single-ended,
input-to-differential output. The additional 23 Ω, 523 Ω total, at
the input to −IN is to balance the parallel impedance of the
50 Ω source and its 50 Ω termination that drives the
noninverting input.
SOURCE
50Ω
49.9Ω
0.1pF
499Ω
AD9224
523Ω
Figure 46. AD8138 Driving an AD9224, a 12-Bit, 40 MSPS ADC
8
2
1
via a pair of
+
AD8138
+5V
–5V
V
3
6
OCM
499Ω
499Ω
5
4
Rev. F | Page 21 of 24
49.9Ω
49.9Ω
The signal generator has a ground-referenced, bipolar output,
that is, it drives symmetrically above and below ground.
Connecting V
common-mode of the AD8138 at 2.5 V, which is the midsupply
level for the AD9224. This voltage is bypassed by a 0.1 μF
capacitor.
The full-scale analog input range of the
4 V p-p, by shorting the SENSE terminal to AVSS. This has
been determined to be the scaling to provide minimum
harmonic distortion.
For the AD8138 to swing at 4 V p-p, each output swings 2 V p-p
while providing signals that are 180° out of phase. With a
common-mode voltage at the output of 2.5 V, each AD8138
output swings between 1.5 V and 3.5 V.
A ground-referenced 4 V p-p, 5 MHz signal at D
test the circuit in Figure 46. When the combined-device circuit
was run with a sampling rate of 20 MSPS, the spurious-free
dynamic range (SFDR) was measured at −85 dBc.
24
23
VINB
VINA
0.1pF
AVSS
AVDD
15 26
16 25
OCM
+5V
AD9224
DRVDD
SENSE
to the CML pin of the
28
17
0.1pF
CML
22
DRVSS
27
DIGITAL
OUTPUTS
AD9224
AD9224
IN
is set to
sets the output
+ was used to
AD8138

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