MAX1184ECM+TD Maxim Integrated Products, MAX1184ECM+TD Datasheet - Page 17

• Manufacturer Part Number: MAX1184ECM+TD
• Description: IC ADC 10BIT 20MSPS DL 48-TQFP
• Manufacturer: Maxim Integrated Products

Specifications of MAX1184ECM+TD

• Number Of Bits: 10
• Sampling Rate (per Second): 20M
• Data Interface: Parallel
• Number Of Converters: 2
• Power Dissipation (max): 150mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-TQFP Exposed Pad, 48-eTQFP, 48-HTQFP, 48-VQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The most frequently used modulation technique for digi-
tal communications applications is probably the quadra-
ture 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 baseband
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 component is 90 degree
phase-shifted with respect to the in-phase component. At
the receiver, the QAM signal is divided down into it’s I
and Q components, essentially representing the modula-
tion process reversed. Figure 8 displays the demodula-
tion process performed in the analog domain, using the
dual matched 3V, 10-bit ADC (MAX1184), and the
MAX2451 quadrature demodulator to recover and digi-
tize the I and Q baseband signals. Before being digitized
by the MAX1184, the mixed down-signal components
may be filtered by matched analog filters, such as
Nyquist or pulse-shaping filters, which remove any
unwanted images from the mixing process, thereby
enhancing the overall signal-to-noise (SNR) performance
and minimizing intersymbol interference.
The MAX1184 requires high-speed board layout design
techniques. Locate all bypass capacitors as close to the
device as possible, preferably on the same side as the
ADC, using surface-mount devices for minimum induc-
tance. Bypass V
Figure 8. Typical QAM Application, Using the MAX1184
Typical QAM Demodulation Application
Dual 10-Bit, 20Msps, 3V, Low-Power ADC with
Grounding, Bypassing, and
DD
______________________________________________________________________________________
Internal Reference and Parallel Outputs
, REFP, REFN, and COM with two
Board Layout
DOWNCONVERTER
MAX2451
parallel 0.1µF ceramic capacitors and a 2.2µF bipolar
capacitor to GND. Follow the same rules to bypass the
digital supply (OV
separated ground and power planes produce the high-
est level of signal integrity. Consider the use of a split
ground plane arranged to match the physical location of
the analog ground (GND) and the digital output driver
ground (OGND) on the ADC’s package. The two ground
planes should be joined at a single point such that the
noisy digital ground currents do not interfere with the
analog ground plane. The ideal location of this connec-
tion can be determined experimentally at a point along
the gap between the two ground planes, which pro-
duces optimum results. Make this connection with a low-
value, surface-mount resistor (1Ω to 5Ω), a ferrite bead,
or a direct short. Alternatively, all ground pins could
share the same ground plane, if the ground plane is suf-
ficiently isolated from any noisy, digital systems ground
plane (e.g., downstream output buffer or DSP ground
plane). Route high-speed digital signal traces away
from the sensitive analog traces of either channel. Make
sure to isolate the analog input lines to each respective
converter to minimize channel-to-channel crosstalk.
Keep all signal lines short and free of 90 degree turns.
Integral nonlinearity is the deviation of the values on an
actual transfer function from a straight line. This straight
line can be either a best straight-line fit or a line drawn
between the endpoints of the transfer function, once
offset and gain errors have been nullified. The static lin-
earity parameters for the MAX1184 are measured using
the best straight-line fit method.
÷ 8
Static Parameter Definitions
0°
90°
DD
) to OGND. Multilayer boards with
Integral Nonlinearity (INL)
INA+
INA-
INB+
INB-
MAX1184
PROCESSING
POST
DSP
17