Datasheet

MAX1184
Dual 10-Bit, 20Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
16 ______________________________________________________________________________________
MAX1184
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 7: Using an Op Amp for Single-Ended, AC-Coupled
Input Drive
Using Transformer Coupling
A RF transformer (Figure 6) provides an excellent solu-
tion to convert a single-ended source signal to a fully
differential signal, required by the MAX1184 for opti-
mum performance. Connecting the center tap of the
transformer 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
requirements. A reduced signal swing from the input
driver, such as an op amp, may also improve the over-
all distortion.
In general, the MAX1184 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 a 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.
Figure 6. Transformer-Coupled Input Drive
MAX1184
T1
N.C.
V
IN
6
1
5
2
43
22pF
22pF
0.1µF
0.1µF
2.2µF
25Ω
25Ω
MINICIRCUITS
TT1–6
T1
N.C.
V
IN
6
1
5
2
4
3
22pF
22pF
0.1µF
0.1µF
2.2µF
25Ω
25Ω
MINICIRCUITS
TT1–6
INA-
INA+
INB-
INB+
COM