MAX1192 Datasheet, PDF (21/28 Pages) Maxim Integrated Products – Ultra-Low-Power, 22Msps, Dual 8-Bit ADC

Ultra-Low-Power, 22Msps, Dual 8-Bit ADC
25Ω
22pF
0.1µF
V_IN
1 T1 6
N.C. ²
5
2.2µF 0.1µF
3
4
MINICIRCUITS
TT1-6-KK81
25Ω
22pF
25Ω
22pF
0.1µF
V_IN
1 T1 6
N.C. ²
5
2.2µF 0.1µF
3
4
MINICIRCUITS
TT1-6-KK81
25Ω
22pF
INA+
COM
INA-
MAX1192
INB+
INB-
REFP
V_IN
MAX4108
100Ω
0.1µF
1kΩ _RISO
50Ω
C_IN
1kΩ
22pF
100Ω
REFN
REFP
0.1µF
R_ISO
50Ω
C_IN
22pF
V_IN
0.1µF
MAX4108
100Ω
1kΩ RISO
50Ω
C_IN
1kΩ
22pF
100Ω
REFN
0.1µF
R_ISO
50Ω
C_IN
22pF
INA+
COM
INA-
MAX1192
INB+
INB-
Figure 8. Transformer-Coupled Input Drive
Using Transformer Coupling
An RF transformer (Figure 8) provides an excellent
solution to convert a single-ended source signal to a
fully differential signal, required by the MAX1192 for
optimum performance. Connecting the center tap of the
transformer to COM provides a V_DD/2 DC level shift to
the input. Although a 1:1 transformer is shown, a step-
up transformer can be selected to reduce the drive
requirements. A reduced signal swing from the input
driver, such as an op amp, can also improve the overall
distortion.
In general, the MAX1192 provides better SFDR and
THD with fully differential input signals than single-
ended drive, especially for high input frequencies. In
differential input mode, even-order harmonics are lower
as both inputs (INA+, INA- and/or INB+, INB-) are bal-
Figure 9. Using an Op Amp for Single-Ended, AC-Coupled
Input Drive
anced, and each of the ADC inputs only requires half
the signal swing compared to single-ended mode.
Single-Ended AC-Coupled Input Signal
Figure 9 shows an AC-coupled, single-ended applica-
tion. Amplifiers such as the MAX4108 provide high
speed, high bandwidth, low noise, and low distortion to
maintain the input signal integrity.
Buffered External Reference Drives
Multiple ADCs
The buffered external reference mode allows for more
control over the MAX1192 reference voltage and allows
multiple converters to use a common reference. To
drive one MAX1192 in buffered external reference
mode, the external circuit must sink 0.7µA, allowing one
reference circuit to easily drive the REFIN of multiple
converters to 1.024V ±10%.
______________________________________________________________________________________ 21