Maxim recommends using microstrip and stripline tech-
niques to obtain full bandwidth. To ensure that the PC
board does not degrade the amplifier’s performance,
design it for a frequency greater than 1GHz. Pay care-
ful attention to inputs and outputs to avoid large para-
sitic capacitance. Whether or not you use a constant-
impedance board, observe the following guidelines
when designing the board:
•Don’t use wire-wrap boards because they are too
inductive.
•Don’t use IC sockets because they increase parasitic
capacitance and inductance.
•Use surface-mount instead of through-hole compo-
nents for better high-frequency performance.
•Use a PC board with at least two layers; it should be
as free from voids as possible.
•Keep signal lines as short and as straight as possi-
ble. Do not make 90° turns; round all corners.
Rail-to-Rail Outputs,
Ground-Sensing Input
The input common-mode range extends from
(VEE - 200mV) to (VCC - 2.25V) with excellent common-
mode rejection. Beyond this range, the amplifier output
is a nonlinear function of the input, but does not under-
go phase reversal or latchup.
The output swings to within 60mV of either power-
supply rail with a 2kΩload. The input ground-sensing
and the rail-to-rail output substantially increase the
dynamic range. With a symmetric input in a single 5V
application, the input can swing 2.95VP-P, and the out-
put can swing 4.9VP-P with minimal distortion.
Enable Input and Disabled Output
The enable feature (EN_) allows the amplifier to be
placed in a low-power, high-output-impedance state.
Typically, the EN_ logic low input current (IIL) is small.
However, as the EN voltage (VIL) approaches the nega-
tive supply rail, IIL increases (Figure 2). A single resis-
tor connected as shown in Figure 3 prevents the rise in
the logic-low input current. This resistor provides a
feedback mechanism that increases VIL as the logic
input is brought to VEE. Figure 4 shows the resulting
input current (IIL).
When the MAX4018 is disabled, the amplifier’s output
impedance is 35kΩ. This high resistance and the low
2pF output capacitance make this part ideal in
RF/video multiplexer or switch applications. For larger
arrays, pay careful attention to capacitive loading. See
the Output Capacitive Loading and Stability section for
more information.
MAX4012/MAX4016/MAX4018/MAX4020
Low-Cost, High-Speed, Single-Supply
Op Amps with Rail-to-Rail Outputs
______________________________________________________________________________________ 11
RF(Ω)24 500
RG(Ω)∞500
COMPONENT
RS(Ω)— 0
RTIN (Ω)49.9 56
Small-Signal -3dB Bandwidth (MHz) 200 90
RTO (Ω)49.9 49.9
Table 1. Recommended Component Values
Note: RL= RO+ RTO; RTIN and RTO are calculated for 50Ωapplications. For 75Ωsystems, RTO = 75Ω; calculate RTIN from the
following equation:
500
500
—
49.9
105
49.9
500
250
0
62
60
49.9
500
124
—
49.9
25
49.9
500
100
0
100
33
49.9
500
56
—
49.9
11
49.9
500
50
0
∞
25
49.9
500
20
—
49.9
6
49.9
GAIN (V/V)
1200
50
0
∞
10
49.9
+1 -1 +2 -2 +5 -5 +10 -10 +25 -25