Rainbow Electronics MAX1425 - Manual (Page 13)

MAX1425
10-Bit, 20Msps ADC
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octal D-latched flip-flop (74ALS374), or use octal
buffers such as the 74ALS541.
Typical Application Using an
External Reference
Figure 7 depicts an application circuit that shuts down
the internal reference, allowing an external reference to
be used for selecting a different common-mode volt-
age. This added flexibility also allows for ratiometric
conversions, as well as for calibration.
Using Transformer Coupling
A small transformer (Figure 8) provides isolation and
AC-coupling to the ADC’s input. Connecting the trans-
former’s center tap to CML provides a +2.25VDC level
shift to the input. Transformer coupling reduces the
need for high-speed op amps, thereby reducing cost.
Although a 1:1 transformer is shown, a step-up trans-
former may be selected to reduce the drive require-
ments.
Single-Ended DC-Coupled Input Signal
Figure 9 shows an AC-coupled, single-ended applica-
tion. The MAX4108 quad op amp provides high speed,
high bandwidth, low noise, and low distortion to main-
tain the integrity of the input signal.
4.5k
CMLP
INP
INN
CMLN
4.5k
TO T/H INPUT
5.5k 5.5k
Figure 6. Analog Input DC Bias Circuit
Figure 7. Using an External Reference for REFP, REFN, and CML (internal reference shut down)
MAX1425
REFIN
REFN
R
50 Ω
R
R
R
R
+1V
R
50 Ω
50 Ω
R
R
V DD
V DD
2
CML
0.1 µF
0.1 µF
0.1 µF
AGND
V DD
2
V DD
2
V DD
4
V DD
4
MAX4284
MAX4284
( )
V DD
2
- 1V
( )
REFP
V DD
2
+ 1V
( )