MAX1190 Datasheet, PDF (16/21 Pages) Maxim Integrated Products – Dual 10-Bit, 120Msps, 3.3V, Low-Power ADC with Internal Reference and Parallel Outputs

Dual 10-Bit, 120Msps, 3.3V, Low-Power ADC
with Internal Reference and Parallel Outputs
REFP
V_IN
0.1µF
1kΩ _RISO
50Ω
MAX4108
100Ω
C_IN
1kΩ
22pF
100Ω
REFN _0.1µF
REFP
R_ISO
50Ω
C_IN
22pF
V_IN
0.1µF
1kΩ RISO
50Ω
MAX4108
100Ω
C_IN
1kΩ
22pF
INA+
COM
INA-
MAX1190
INB+
100Ω
REFN _0.1µF
R_ISO
50Ω
INB-
C_IN
22pF
Figure 7. Using an Op Amp for Single-Ended, AC-Coupled Input Drive
high-gain accuracy) and a low noise level. The passive
10Hz filter following the buffer attenuates noise pro-
duced in the voltage reference and buffer stages. This
filtered noise density, which decreases for higher fre-
quencies, meets the noise levels specified for preci-
sion-ADC operation.
Unbuffered External Reference Drives
Multiple ADCs
Connecting each REFIN to analog ground disables the
internal reference of each device, allowing the internal
reference ladders to be driven directly by a set of exter-
nal reference sources. Followed by a 10Hz lowpass fil-
ter and precision voltage-divider, the MAX6066
generates a DC level of 2.500V. The buffered outputs of
this divider are set to 2.0V, 1.5V, and 1.0V, with an
accuracy that depends on the tolerance of the divider
resistors (Figure 9).
Those three voltages are buffered by the MAX4252,
which provides low noise and low DC offset. The indi-
vidual voltage followers are connected to 10Hz lowpass
filters, which filter both the reference voltage and ampli-
fier noise to a level of 3nV/√Hz. The 2.0V and 1.0V refer-
ence voltages set the differential full-scale range of the
associated ADCs at 2V_P-P. The 2.0V and 1.0V buffers
drive the ADCs’ internal ladder resistances between
them. Note that the common power supply for all active
components removes any concern regarding power-
supply sequencing when powering up or down.
With the outputs of the MAX4252 matching better than
0.1%, the buffers and subsequent lowpass filters can
be replicated to support as many as 32 ADCs. For
applications that require more than 32 matched ADCs,
a voltage reference and divider string common to all
converters is highly recommended.
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