Datasheet
MAX19707
10-Bit, 45Msps, Ultra-Low-Power
Analog Front-End
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Reference Configurations
The MAX19707 features an internal precision 1.024V
bandgap reference that is stable over the entire power-
supply and temperature ranges. The REFIN input pro-
vides two modes of reference operation. The voltage at
REFIN (V
REFIN
) sets the reference operation mode
(Table 17).
In internal reference mode, connect REFIN to V
DD
.
V
REF
is an internally generated 0.512V ±4%. COM,
REFP, and REFN are low-impedance outputs with
V
COM
= V
DD
/ 2, V
REFP
= V
DD
/ 2 + V
REF
/ 2, and
V
REFN
= V
DD
/ 2 - V
REF
/ 2. Bypass REFP, REFN, and
COM each with a 0.33µF capacitor. Bypass REFIN to
GND with a 0.1µF capacitor.
In buffered external reference mode, apply 1.024V
±10% at REFIN. In this mode, COM, REFP, and REFN
are low-impedance outputs with V
COM
= V
DD
/ 2,
V
REFP
= V
DD
/ 2 + V
REFIN
/ 4, and V
REFN
= V
DD
/ 2 -
V
REFIN
/ 4. Bypass REFP, REFN, and COM each with a
0.33µF capacitor. Bypass REFIN to GND with a 0.1µF
capacitor. In this mode, the Tx DAC full-scale output is
proportional to the external reference. For example, if
the V
REFIN
is increased by 10% (max), the Tx DAC full-
scale output is also increased by 10% or ±440mV.
Applications Information
Using Balun Transformer AC-Coupling
An RF transformer (Figure 8) provides an excellent
solution to convert a single-ended signal source to a
fully differential signal for optimum ADC performance.
Connecting the center tap of the transformer to COM
provides a V
DD
/ 2 DC level shift to the input. A 1:1
transformer can be used, or a step-up transformer can
be selected to reduce the drive requirements. In gener-
al, the MAX19707 provides better SFDR and THD with
fully differential input signals than single-ended signals,
especially for high input frequencies. In differential
mode, even-order harmonics are lower as both inputs
(IAP, IAN, QAP, QAN) are balanced, and each of the
Rx ADC inputs only requires half the signal swing com-
pared to single-ended mode. Figure 9 shows an RF
transformer converting the MAX19707 Tx DAC differen-
tial analog outputs to single-ended.
Table 17. Reference Modes
V
REFIN
REFERENCE MODE
> 0.8V x V
DD
Internal Reference Mode. V
REF
is internally generated to be 0.512V. Bypass REFP, REFN, and COM each
with a 0.33µF capacitor.
1.024V ±10%
Buffered External Reference Mode. An external 1.024V ±10% reference voltage is applied to REFIN. V
REF
is
internally generated to be V
REFIN
/ 2. Bypass REFP, REFN, and COM each with a 0.33µF capacitor. Bypass
REFIN to GND with a 0.1µF capacitor.
Figure 8. Balun Transformer-Coupled Single-Ended-to-
Differential Input Drive for Rx ADC
COM
IAP
IAN
25
Ω
0.1
μ
F
0.33
μ
F
25
Ω
0.1
μ
F
V
IN
MAX19707
22pF
22pF
QAP
QAN
25
Ω
0.1
μ
F
0.33
μ
F
25
Ω
0.1
μ
F
V
IN
22pF
22pF