Datasheet

APPLICATION INFORMATION
WIDEBAND BUFFER OPERATION
1/3
OPA3695
+5V
-5V
50 LoadW
50W
50W
50 SourceW
R
G
R
F
+
6.8 Fm0.1 Fm
+
6.8 Fm0.1 Fm
V
I
V
O
DIS
OPA3695
www.ti.com ............................................................................................................................................... SBOS355A – APRIL 2008 – REVISED SEPTEMBER 2008
The OPA3695 gives the exceptional ac performance
of a wideband current-feedback op amp with a highly
linear output stage. Requiring only 12.9mA/channel
supply current, the OPA3695 achieves a 900MHz
small-signal bandwidth (G = +2V/V); the high slew
rate capability of up to 4300V/ µ s supports a 600MHz
2V
PP
large signal into a 100 Ω load. The low output
headroom of 1V from either supply in a very
high-speed amplifier gives very good single +5V
operation. The OPA3695 delivers a 2V
PP
swing with
greater than 400MHz bandwidth operating on a single
+5V supply. The primary advantage of a
current-feedback video buffer (as opposed to a
slew-enhanced, low-gain, stable voltage-feedback
implementation) is a higher slew rate with lower
quiescent power and output noise.
Figure 35. DC-Coupled, Noninverting,
Figure 35 shows the dc-coupled, noninverting, dual
Bipolar-Supply, Specification and Test Circuit
power-supply circuit configuration used as the basis
for the ± 5V Electrical Characteristics table and
Typical Characteristics curves. For test purposes, the Figure 36 illustrates the dc-coupled, inverting
input impedance is set to 50 Ω with a resistor to configuration used as the basis of the Inverting
ground; the output impedance is set to 50 Ω with a Typical Characteristic curves. Inverting operation
series output resistor. Voltage swings reported in the offers several performance benefits. Since there is no
specifications are taken directly at the input and common-mode signal across the input stage, the slew
output pins while load powers (dBm) are defined at a rate for inverting operation is higher and the distortion
matched 50 Ω load. For the circuit of Figure 35 , the performance is slightly improved. An additional input
total effective amplifier loading is 100 Ω || (R
F
+ R
G
) . resistor, R
M
, is included in Figure 36 to set the input
For example, with a gain of +2V/V with R
F
and R
G
impedance equal to 50 Ω . The parallel combination of
equal to 604 Ω , the equivalent amplifier loading is R
M
and R
G
sets the input impedance. Both the
100 Ω || 1208 Ω = 92.3 Ω . The disable control line noninverting and inverting applications of Figure 35
( DIS) is typically left open to ensure normal amplifier and Figure 36 benefit from optimizing the feedback
operation. Note that while most of the information resistor (R
F
) value for bandwidth (see the discussion
presented in this data sheet was characterized with in the Gain Setting section). The typical design
100 Ω loading, performance with a standard video sequence is to select the R
F
value for best
loading of 150 Ω has negligible impact on bandwidth, set R
G
for the gain, and then set R
M
for
performance. Any changes in performance are the desired input impedance. As the gain increases
typically improved over 100 Ω loading because of for the inverting configuration, a point is reached
lower output current demands. where R
G
equals 50 Ω and R
M
is removed; thus, the
input match is set by R
G
only. With R
G
fixed to
achieve an input match to 50 Ω , R
F
is simply
increased to increase gain. This approach, however,
quickly reduces the achievable bandwidth at such
high gains. For gains greater than 10V/V,
noninverting operation is recommended to maintain
broader bandwidth.
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