Instruction Manual

MAX1198
requirements. A reduced signal swing from the input
driver, such as an op amp, can also improve the overall
distortion.
In general, the MAX1198 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 MAX1198 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 out-
put 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 volt-
age (for high gain accuracy) and a low noise level. The
passive 10Hz filter following the buffer attenuates noise
produced in the voltage reference and buffer stages.
This filtered noise density, which decreases for higher
frequencies, meets the noise levels specified for preci-
sion ADC operation.
Dual, 8-Bit, 100Msps, 3.3V, Low-Power ADC
with Internal Reference and Parallel Outputs
16 ______________________________________________________________________________________
MAX1198
T1
N.C.
V
IN
6
1
5
2
43
22pF
22pF
0.1
µ
F
0.1
µ
F
2.2
µ
F
25
Ω
25
Ω
MINICIRCUITS
TT1–6-KK81
T1
N.C.
V
IN
6
1
5
2
4
3
22pF
22pF
0.1
µ
F
0.1
µ
F
2.2
µ
F
25
Ω
25
Ω
MINICIRCUITS
TT1-6-KK81
INA-
INA+
INB-
INB+
COM
MAX1198
0.1µF
1kΩ
1kΩ
100Ω
100Ω
C
IN
22pF
C
IN
22pF
INB+
INB-
COM
INA+
INA-
0.1µF
R
ISO
50Ω
R
ISO
50Ω
REFP
REFN
V
IN
MAX4108
0.1µF
1kΩ
1kΩ
100Ω
100Ω
C
IN
22pF
C
IN
22pF
0.1µF
R
ISO
50Ω
R
ISO
50Ω
REFP
REFN
V
IN
MAX4108
Figure 6. Transformer-Coupled Input Drive
Figure 7. Using an Op Amp for Single-Ended, AC-Coupled
Input Drive