Ultra-Small, Low-Cost, 210MHz, Single-Supply
Op Amps with Rail-to-Rail Outputs
Table 1. Recommended Component Values
GAIN (V/V)
COMPONENT
+1
±4
-1
500
500
0
+2
500
500
—
-2
500
±50
0
+5
500
1±4
—
-5
500
100
0
+10
500
56
-10
500
50
+25
500
±0
-25
1±00
50
R (Ω)
F
∞
R
(Ω)
G
R (Ω)
S
—
—
0
—
0
∞
∞
R
R
(Ω)
(Ω)
49.9
49.9
±10
56
49.9
49.9
95
6±
49.9
49.9
±5
100
49.9
±5
49.9
49.9
11
49.9
49.9
5
TIN
TO
49.9
100
49.9
50
49.9
15
49.9
10
Small-Signal -3dB Bandwidth (MHz)
Note:
R
= R + R ; R
and R
are calculated for 50Ω applications. For 75Ω systems, R
TO
= 75Ω; calculate R from the
TIN
L
O
TO
TIN
TO
following equation:
75
R
=
Ω
TIN
75
1-
R
G
0.1µF capacitor as close to the pin as possible. If operat-
ing with dual supplies, bypass each supply with a 0.1µF
capacitor.
and the rail-to-rail output substantially increase the
dynamic range. With a symmetric input in a single +5V
application, the input can swing ±.95Vp-p and the out-
put can swing 4.9Vp-p with minimal distortion.
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 design guide-
lines:
Output Capacitive Loading and Stability
The MAX4450/MAX4451 are optimized for AC perfor-
mance. They are not designed to drive highly reactive
loads, which decrease phase margin and may produce
excessive ringing and oscillation. Figure ± shows a cir-
cuit that eliminates this problem. Figure 3 is a graph of
the optimal isolation resistor (R ) vs. capacitive load.
S
• Don’t use wire-wrap boards; they are too inductive.
Figure 4 shows how a capacitive load causes exces-
sive peaking of the amplifier’s frequency response if
the capacitor is not isolated from the amplifier by a
resistor. A small isolation resistor (usually ±0Ω to 30Ω)
placed before the reactive load prevents ringing and
oscillation. At higher capacitive loads, AC performance
is controlled by the interaction of the load capacitance
and the isolation resistor. Figure 5 shows the effect of a
±7Ω isolation resistor on closed-loop response.
• Don’t use IC sockets; they increase parasitic capaci-
tance 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.
Coaxial cable and other transmission lines are easily
driven when properly terminated at both ends with their
characteristic impedance. Driving back-terminated
transmission lines essentially eliminates the line’s
capacitance.
Rail-to-Rail Outputs,
Ground-Sensing Input
The input common-mode range extends from
(V - ±00mV) to (V
EE
- ±.±5V) with excellent common-
CC
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 55mV of either power-
supply rail with a ±kΩ load. The input ground sensing
8
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
