MAX1419
15-Bit, 65Msps ADC with -79.3dBFS
Noise Floor for Baseband Applications
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Detailed Description
Figure 1 provides an overview of the MAX1419 archi-
tecture. The MAX1419 employs an input T/H amplifier,
which has been optimized for low thermal noise and
low distortion. The high-impedance differential inputs to
the T/H amplifier (INP and INN) are self-biased at
3.38V, and support a full-scale differential input voltage
of 2.56V
P-P
. The output of the T/H amplifier is fed to a
multistage pipelined ADC core, which has also been
optimized to achieve a very low thermal noise floor and
low distortion.
A clock buffer receives a differential input clock wave-
form and generates a low-jitter clock signal for the input
T/H. The signal at the analog inputs is sampled at the
rising edge of the differential clock waveform. The dif-
ferential clock inputs (CLKP and CLKN) are high-
impedance inputs, are self-biased at 2.4V, and support
differential clock waveforms from 0.5V
P-P
to 3.0V
P-P
.
The outputs from the multistage pipelined ADC core
are delivered to error correction and formatting logic-
which in turn, deliver the 15-bit output code in two’s-
complement format to digital output drivers. The output
drivers provide CMOS-compatible outputs with levels
programmable over a 2.3V to 3.5V range.
Analog Inputs and
Common Mode (INP, INN, CM)
The signal inputs to the MAX1419 (INP and INN) are
balanced differential inputs. This differential configura-
tion provides immunity to common-mode noise coupling
and rejection of even-order harmonic terms. The differ-
ential signal inputs to the MAX1419 should be AC-cou-
pled and carefully balanced in order to achieve the best
dynamic performance (see the Applications Information
section for more detail). AC-coupling of the input signal
is easily accomplished because the MAX1419 inputs
are self-biasing as illustrated in Figure 2. Although the
T/H inputs are high impedance, the actual differential
input impedance is nominally 1kΩ because of the two
500Ω bias resistors connected from each input to the
common-mode reference.
The CM pin provides a monitor of the input common-
mode self-bias potential. In most applications, in which
the input signal is AC-coupled, this pin is not connect-
ed. If DC-coupling of the input signal is required, this
pin may be used to construct a DC servo loop to con-
trol the input common-mode potential. See the
Applications Information section for more details.
