EVAL-CED1Z3 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-CED1Z3' PDF : 28 Pages View PDF
AD7626
DRIVING THE AD7626
Differential Analog Input Source
Figure 33 shows an ADA4899-1 driving each differential input
to the AD7626.
Single-Ended-to-Differential Driver
For applications using unipolar analog signals, a single-
ended-to-differential driver (as shown in Figure 32) allows
for a differential input into the part. This configuration, when
provided with an input signal of 0 V to 4.096 V, produces a
differential ±4.096 V with midscale at 2.048 V. The one-pole
filter using R = 20 Ω and C = 56 pF provides a corner frequency
of 140 MHz. The VCM output of the AD7626 can be buffered
and then used to provide the required 2.048 V common-mode
voltage.
Single-Ended or Fully Differential High Frequency Driver
In applications that require higher input frequency tones, the
ADA4932-1 can be used to drive the inputs to the AD7626. The
ADA4932-1 is a differential driver, which also allows the user
the option of single-ended-to-differential conversion.
Figure 34 shows the typical circuit for a 50 Ω source impedance
(ac-coupled in this example). The input to the ADA4932-1 is
configured to be balanced to the source impedance (in this case
50 Ω). Further information on balancing the input impedance
to the source impedance can be found on the ADA4932-1
datasheet. The circuit shown in Figure 34 operates with an
overall gain of ~0.5 when the termination input termination
is taken into account.
Alternatively, the ADA4932-1 can be used with a fully diffe-
rential source—it acts as an inverting differential driver.
ANALOG INPUT
(UNIPOLAR 0V TO 4.096V)
ADA4899-1
U1
100nF
590Ω
20Ω
590Ω
56pF
IN+
AD7626
20Ω
U2
ADA4899-1
V+
IN–
VCM
56pF
100nF
50Ω
AD8031, AD8032
V–
Figure 32. Single-Ended-to-Differential Driver Circuit Using ADA4899-1
REF1
CREF
10µF2
+VS
CREF
10µF2
REF1
0V TO VREF
ADA4899-1 –VS
+VS
VREF TO 0V
ADA4899-1 –VS
20Ω
56pF
20Ω
56pF
+VS
REF REFIN
IN+
AD7626
IN–
GND
VCM
2.048V
VCM
BUFFERED VCM PIN OUTPUT
GIVES THE REQUIRED 2.048V
COMMON-MODE SUPPLY FOR
ANALOG INPUTS.
0.1µF
AD8031, AD8032
–VS
1SEE THE VOLTAGE REFERENCE OPTIONS SECTION. CONNECTION TO EXTERNAL REFERENCE SIGNALS
IS DEPENDENT ON THE EN1 AND EN0 SETTINGS.
2CREF IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESL AND ESR.
DECOUPLE REF AND REFIN PINS AS PER THE EN1 AND EN0 RECOMMENDATIONS
Figure 33. Driving the AD7626 from a Differential Analog Source Using ADA4899-1
Rev. A | Page 18 of 8
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