ada4937-2 Analog Devices, Inc., ada4937-2 Datasheet - Page 25

• Manufacturer Part Number: ada4937-2
• Description: Ultralow Distortion Differential Adc Driver
• Manufacturer: Analog Devices, Inc.

3.3 V OPERATION
The ADA4937 provides excellent performance in 3.3 V single-
supply applications. Significant power savings can be realized
when the ADA4937 is used in combination with a low
voltage ADC.
The circuit in Figure 64 is an example of the ADA4937 driving
an AD9230, 12-bit, 250 MSPS ADC that is specified to operate
with a single 1.8 V supply. The performance of the ADC is
optimized when it is driven differentially, making the best use of
the signal swing available within the 1.8 V supply. The ADA4937
performs the single-ended-to-differential conversion, common-
mode level-shifting, and buffering of the driving signal.
The ADA4937 is configured with a single 3.3 V supply and a
gain of 2 V/V for a single-ended input to differential output. The
50Ω
V
IN
59Ω
Figure 64. ADA4937 Driving an AD9230, a 12-Bit, 250 MSPS ADC
200Ω
226Ω
V
OCM
ADA4937
+
453Ω
453Ω
3.3V
Rev. A | Page 25 of 28
33Ω
33Ω
10pF
56nH
56nH
59 Ω termination resistor, in parallel with the single-ended input
impedance of 306 Ω, provides a 50 Ω termination for the source.
The additional 26 Ω (226 Ω total) at the inverting input balances
the parallel impedance of the 50 Ω source and termination
resistor driving the noninverting input. The signal generator has
a symmetric, ground-referenced bipolar output. The V
connected to the CML output of the AD9230, and sets the output
common mode of the ADA4937 at 1.4 V. One third of the output
common-mode voltage of the amplifier is fed back to the
summing nodes, biasing −IN and +IN at ~0.5 V. For a common-
mode voltage of 1.4 V, each ADA4937 output swings between
1.09 V and 1.71 V, providing a 1.25 V p-p differential output.
A third-order, 125 MHz, low-pass filter between the ADA4937
and the AD9230 reduces the noise bandwidth of the amplifier
and isolates the driver outputs from the ADC inputs.
30pF
VIN–
VIN+
AVDD
AGND
AD9230
1.8V
DRVDD
CML
ADA4937-1/ADA4937-2
D11 TO
D0
OCM
pin is