MAX1190
Dual 10-Bit, 120Msps, 3.3V, Low-Power ADC
with Internal Reference and Parallel Outputs
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Using Transformer Coupling
An RF transformer (Figure 6) provides an excellent solu-
tion to convert a single-ended source signal to a fully dif-
ferential signal, required by the MAX1190 for optimum
performance. Connecting the center tap of the trans-
former 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 require-
ments. A reduced signal swing from the input driver, such
as an op amp, can also improve the overall distortion.
In general, the MAX1190 provides better SFDR and
THD with fully differential input signals than single-
ended drive, especially for very high input frequencies.
In differential input mode, even-order harmonics are
lower as both inputs (INA+, INA- and/or INB+, INB-) are
balanced, and each of the ADC inputs only requires
half the signal swing compared to single-ended mode.
Single-Ended AC-Coupled Input Signal
Figure 7 shows an AC-coupled, single-ended applica-
tion. Amplifiers like the MAX4108 provide high speed,
high bandwidth, low noise, and low distortion to main-
tain the integrity of the input signal.
Buffered External Reference Drives
Multiple ADCs
Multiple-converter systems based on the MAX1190 are
well suited for use with a common reference voltage.
The REFIN pin of those converters can be connected
directly to an external reference source.
A precision bandgap reference like the MAX6062 gen-
erates an external DC level of 2.048V (Figure 8), and
exhibits a noise voltage density of 150nV/√Hz. Its output
passes through a 1-pole lowpass filter (with 10Hz cutoff
frequency) to the MAX4250, which buffers the reference
before its output is applied to a second 10Hz lowpass
filter. The MAX4250 provides a low offset voltage (for
