
MAX4180–MAX4187
Single/Dual/Quad, 270MHz, 1mA, SOT23,
Current-Feedback Amplifiers with Shutdown
18
______________________________________________________________________________________
The MAX4180–MAX4187 have a very low, 2nV/
√Hz
noise voltage. The current noise at the positive input
(in+) is 4pA/
√Hz, and the current noise at the inverting
input is 5pA/
√Hz.
An example of the DC error calculations, using the
MAX4180 typical data and typical operating circuit
where RF = RG = 1.2k
(RF || RG = 600) and
RS = 37.5
, gives the following:
Calculating the total output noise in a similar manner
yields:
With a 200MHz system bandwidth, this calculates to
102VRMS (approximately 612Vp-p, choosing the six-
sigma value).
Video Line Driver
The MAX4180–MAX4187 are well suited to drive coaxi-
al transmission lines when the cable is terminated at
both ends, as shown in Figure 6. Cable-frequency
response can cause variations in the signal’s flatness.
See Table 1 for optimum RF and RG values.
Driving Capacitive Loads
The MAX4180–MAX4187 are optimized for AC perfor-
mance. They are not designed to drive highly capaci-
tive loads. Reactive loads decrease phase margin and
may produce excessive ringing and oscillation. Figure
7a shows a circuit that eliminates this problem. Placing
the small (usually 5
to 22) isolation resistor, RS,
before the reactive load prevents ringing and
oscillation. At higher capacitive loads, the interaction of
the load capacitance and isolation resistor controls AC
performance. Figures 7b and 7c show the MAX4180
and MAX4181 frequency response with a 47pF capaci-
e1 1
4 x 10
x 37.5
5 x 10
x 255
2x10
e
4.8nV/ Hz
n(OUT)
12
2
12
2
9
2
n(OUT)
=+
()
+
+
=
V
1x10
x37.5
2x10
x 600
1.5x10
x 1 1
V
4.1mV
OUT
66
3
=+
+
=
()
()
VIDEO
IN
VIDEO
OUT
75
75
CABLE
VIDEO LINE DRIVER
75
CABLE
RF
820
RG
820
75
75
+5V
-5V
MAX4180
0.1F
Figure 6. Video Line Driver
VOUT
RG
RS
VOUT = -(RF / RG) x VIN
VIN
RF
RO
RT
MAX4180–MAX4187
Figure 4a. Inverting Gain Configuration
VOUT
RG
RS
VOUT = [1+ (RF / RG) VIN
VIN
RF
RO
RT
MAX4180–MAX4187
Figure 4b. Noninverting Gain Configuration
RG
IB-
IB+
VOUT
RF
RS
MAX4180–MAX4187
Figure 5. Output Offset Voltage