ADA4937-1YCPZ-RL Analog Devices Inc, ADA4937-1YCPZ-RL Datasheet - Page 24

• Manufacturer Part Number: ADA4937-1YCPZ-RL
• Description: IC,Differential Amplifier,SINGLE,BIPOLAR,LLCC,16PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Type: ADC Driverr

Specifications of ADA4937-1YCPZ-RL

• Design Resources: Driving AD9233/46/54 ADCs in AC-Coupled Baseband Appls (CN0051)
• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADA4937-1/ADA4937-2
The circuit in Figure 66 shows a simplified front-end connection
for an ADA4937-1 driving an AD9246, 14-bit, 125 MSPS ADC.
The AD9246 achieves its optimum performance when driven
differentially. The ADA4937-x performs the single-ended-to-
differential conversion, eliminating the need for a transformer
to drive the ADC.
The ADA4937-x is configured with a single 5 V supply and a
gain of ~2 V/V for a single-ended input to differential output.
The 76.8 Ω termination resistor, in parallel with the single-ended
input impedance of 137 Ω, provides a 50 Ω ac termination for the
source. The additional 30 Ω (120 Ω total) at the inverting input
balances the parallel ac impedance of the 50 Ω source and the
termination resistor driving the noninverting input.
The signal generator has a symmetric, ground-referenced bipolar
output. The V
therefore, the internal pull-ups set the output common-mode
voltage to midsupply. A portion of this is fed back to the summing
nodes, biasing −IN and +IN at 0.55 V. For a common-mode vol-
tage of 2.5 V, each ADA4937-x output swings between 2.0 V and
3.0 V, providing a 2 V p-p differential output.
The output is ac-coupled to a single-pole, low-pass filter. This
reduces the noise bandwidth of the amplifier and provides some
level of isolation from the switched capacitor inputs of the ADC.
OCM
pin of the ADA4937-x remains unconnected;
50Ω
V
IN
50Ω
10µF
76.8Ω
10µF
76.8Ω
90Ω
90Ω
Figure 66. Driving an AD9246, 14-Bit, 125 MSPS ADC
ADA4937-1
+
200Ω
200Ω
5V
Rev. C | Page 24 of 28
10µF
10µF
200Ω
200Ω
33Ω
33Ω
10pF
The AD9246 is set for a 2 V p-p full-scale input by connecting
the SENSE pin to AGND. The inputs of the AD9246 are biased
at 1 V by connecting the CML output, as shown in Figure 66.
The circuit was tested with a −1 dBFS signal at various frequencies .
Figure 65 shows a plot of the second- and third-order harmonic
distortion (HD2/HD3) vs. frequency.
Figure 65. HD2/HD3 for Combination of ADA4937-x and AD9246 ADC
–100
–75
–80
–85
–90
–95
VIN–
VIN+
0
G = +2
AGND
AVDD
AD9246
1.8V
20
SENSE
DRVDD
CML
40
FREQUENCY (MHz)
D13 TO
D0
60
HD3
80
HD2
100
120