MAX1438B Datasheet, PDF (18/21 Pages) Maxim Integrated Products – Octal, 12-Bit, 64Msps, 1.8V ADC with Serial LVDS Outputs

Octal, 12-Bit, 64Msps, 1.8V ADC
with Serial LVDS Outputs
ADC FULL-SCALE = REFT - REFB
REFERENCE-
SCALING
REFT
AMPLIFIER
G
REFB
REFERENCE
BUFFER
REFIO
1V
CONTROL LINE TO
DISABLE REFERENCE
BUFFER
REFADJ
0.1µF
25kΩ
TO 250kΩ
25kΩ
TO 250kΩ
MAX1438B
AV_CC AV_CC/2
Figure 8. Circuit Suggestions to Adjust the ADC’s Full-Scale
Range
Using Transformer Coupling
An RF transformer (Figure 9) provides an excellent
solution to convert a single-ended input source signal
to a fully differential signal. The MAX1438B input com-
mon-mode voltage is internally biased to 0.76V (typ)
with f_CLK = 64MHz. Although a 1:1 transformer is
shown, a step-up transformer can be selected to
reduce the drive requirements. A reduced signal swing
from the input driver, such as an op amp, can also
improve the overall distortion.
Grounding, Bypassing, and Board Layout
The MAX1438B requires high-speed board layout
design techniques. Refer to the MAX1438B EV kit data
sheet for a board layout reference. Locate all bypass
capacitors as close as possible to the device, prefer-
ably on the same side as the ADC, using surface-mount
devices for minimum inductance. Bypass AVDD to GND
with a 0.1µF ceramic capacitor in parallel with a 0.1µF
ceramic capacitor. Bypass OVDD to GND with a 0.1µF
ceramic capacitor in parallel with a ≥ 2.2µF ceramic
capacitor. Bypass CVDD to GND with a 0.1µF ceramic
capacitor in parallel with a ≥ 2.2µF ceramic capacitor.
Multilayer boards with ample ground and power planes
produce the highest level of signal integrity. Connect
0.1µF
V_IN
1
6
T1
N.C. ²
5
3
4
MINICIRCUITS
ADT1-1WT
10Ω
39pF
0.1µF
10Ω
39pF
IN_P
MAX1438B
IN_N
Figure 9. Transformer-Coupled Input Drive
the MAX1438B ground pins and the exposed backside
pad to the same ground plane. The MAX1438B relies
on the exposed-backside-pad connection for a low-
inductance ground connection. Isolate the ground
plane from any noisy digital system ground planes.
Route high-speed digital signal traces away from the
sensitive analog traces. Keep all signal lines short and
free of 90° turns.
Ensure that the differential analog input network layout
is symmetric and that all parasitics are balanced equal-
ly. Refer to the MAX1438B EV kit data sheet for an
example of symmetric input layout.
Parameter Definitions
Integral Nonlinearity (INL)
INL is the deviation of the values on an actual transfer
function from a straight line. For the MAX1438B, this
straight line is between the end points of the transfer
function, once offset and gain errors have been nulli-
fied. INL deviations are measured at every step and the
worst-case deviation is reported in the Electrical
Characteristics table.
Differential Nonlinearity (DNL)
DNL is the difference between an actual step width and
the ideal value of 1 LSB. A DNL error specification of
less than 1 LSB guarantees no missing codes and a
monotonic transfer function. For the MAX1438B, DNL
deviations are measured at every step and the worst-
case deviation is reported in the Electrical
Characteristics table.
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