Datasheet

AD9653 Data Sheet
Rev. 0 | Page 24 of 40
Figure 56. Differential Double Balun Input Configuration for Baseband Applications
Figure 57. Differential Transformer-Coupled Configuration
for Baseband Applications
If the internal reference of the AD9653 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 58 and
Figure 59 show how the internal reference voltage is affected by
loading.
Figure 58. V
REF
= 1.0 V Error vs. Load Current
Figure 59. V
REF
=1.3 V Error vs. Load Current
External Reference Operation
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift charac-
teristics. Figure 60 and Figure 61 show the typical drift characteris-
tics of the internal reference in 1.0 V mode and programmable
1.3 V mode, respectively.
ADC
R0.1µF
0.1µF
2V p-p
VCM
C
*C1
*C1
C
R
0.1µF
0.1µF 0.1µF
33Ω
200Ω
33Ω
33Ω
33Ω
VIN+x
VIN–x
ET1-1-I3
C
C
5pF
R
*C1 IS OPTIONAL
10538-056
2Vp-p
R
R
*C1
*C1 IS OPTIONAL
49.9Ω
0.1μF
ADT1-1WT
1:1 Z RATIO
VIN–x
ADC
VIN+x
*C1
C
VCM
33Ω
33Ω
200Ω
0.1µF
5pF
10538-057
0
–0.5
–1.0
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
–4.5
–5.0
0 3.02.52.01.51.00.5
V
REF
ERROR (%)
LOAD CURRENT (mA)
INTERNAL V
REF
= 1.0V
10538-058
0
–1
–2
–3
–4
–5
–6
–7
–8
–9
0 3.02.52.01.51.00.5
V
REF
ERROR (%)
LOAD CURRENT (mA)
INTERNAL V
REF
= 1.3V
10538-059