Figure 4 displays the timing relationship between output
enable and data output valid, as well as power-
down/wake-up and data output valid.
Power-Down (PD) and Sleep
(SLEEP) Modes
The MAX1183 offers two power-save modes—sleep and
full power-down modes. In sleep mode (SLEEP = 1), only
the reference bias circuit is active (both ADCs are
disabled), and current consumption is reduced to 2.8mA.
To enter full power-down mode, pull PD high. With OE
simultaneously low, all outputs are latched at the last
value prior to the power down. Pulling OE high forces
the digital outputs into a high-impedance state.
Applications Information
Figure 5 depicts a typical application circuit containing
two single-ended to differential converters. The internal
reference provides a V
DD
/2 output voltage for level-
shifting purposes. The input is buffered and then split
to a voltage follower and inverter. One lowpass filter per
ADC suppresses some of the wideband noise associat-
ed with high-speed op amps follows the amplifiers. The
user may select the R
ISO
and C
IN
values to optimize
the filter performance, to suit a particular application.
For the application in Figure 5, a R
ISO
of 50Ω is placed
before the capacitive load to prevent ringing and
oscillation. The 22pF C
IN
capacitor acts as a small
bypassing capacitor.
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 MAX1183 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 may be selected to reduce the drive require-
ments. A reduced signal swing from the input driver, such
as an op amp, may also improve the overall distortion.
In general, the MAX1183 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.
Typical QAM Demodulation Application
The most frequently used modulation technique for dig-
ital communications applications is probably the quad-
rature amplitude modulation (QAM). Typically found in
spread-spectrum-based systems, a QAM signal repre-
sents a carrier frequency modulated in both amplitude
and phase. At the transmitter, modulating the base-
band signal with quadrature outputs, a local oscillator
followed by subsequent up-conversion can generate
the QAM signal. The result is an in-phase (I) and
a quadrature (Q) carrier component, where the Q
MAX1183
Dual 10-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
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