Datasheet
1/3
OPA3695
+5V
DIS
50W
V
O
R
F
R
G
R
M
+
6.8 Fm0.1 Fm
50 LoadW
-5V
+
6.8 Fm0.1 Fm
50 SourceW
V
I
1/3
OPA3695
+5V
+V
S
DIS
V /2
S
604W
100WV
O
V
I
604W
R
G
49.9W
R
F
348W
0.1 Fm
0.1 Fm
+
6.8 Fm0.1 Fm
50 SourceW
60.4W
SINGLE-SUPPLY OPERATION
OPA3695
SBOS355A – APRIL 2008 – REVISED SEPTEMBER 2008 ...............................................................................................................................................
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simple resistive divider from the +5V supply (two
604 Ω resistors). The input signal is then ac-coupled
into this midpoint voltage bias. The input voltage can
swing to within 1.6V of either supply pin, giving a
1.8V
PP
input signal range centered between the
supply pins. The input impedance matching resistor
(60.4 Ω ) used for testing is adjusted to give a 50 Ω
input match when the parallel combination of the
biasing divider network is included. The gain resistor
(R
G
) is ac-coupled, giving the circuit a dc gain of
+1V/V, which puts the input dc bias voltage (2.5V) on
the output as well. Again, on a single +5V supply, the
output voltage can swing to within 1V of either supply
pin while delivering ± 90mA output current. A
demanding 100 Ω load to a midpoint bias is used in
this characterization circuit. The new output stage
used in the OPA3695 can deliver large bipolar output
Figure 36. DC-Coupled, Inverting, Bipolar-Supply,
current into this midpoint load with minimal crossover
Specification and Test Circuit
distortion, as illustrated by the +5V supply,
third-harmonic distortion plots.
Notice that in this configuration (shown in Figure 36 ),
the noninverting input is tied directly to ground.
Because the internal design for the OPA3695 is
current-feedback, trying to achieve improved dc
accuracy by including a resistor on the noninverting
input to ground is ineffective. Using a direct short to
ground on the noninverting input reduces both the
contribution of the dc bias current and the noise
current to the output error. While the external R
M
is
used here to match with the 50 Ω source from the test
equipment, the input impedance in this configuration
is limited to the R
G
resistor. Removing R
M
does not
strongly impact the dc operating point because the
short on the noninverting input of Figure 36 provides
the dc operating voltage. This application of the
OPA3695 provides a very broadband, high-output
signal inverter.
Figure 37. AC-Coupled, G = +8V/V, Single-Supply
Specification and Test Circuit
The OPA3695 may be used over a single-supply
range of +3.5V to +12V. Though not a rail-to-rail
While the circuit of Figure 37 shows +5V
output design, the OPA3695 requires minimal input
single-supply operation, this same circuit may be
and output voltage headroom compared to other
used for single supplies that range as high as +12V
very-wideband video buffer amplifiers. The key
nominal. The noninverting input bias resistors are
requirement of broadband single-supply operation is
relatively low in Figure 37 to minimize output dc offset
to maintain input and output signal swings within the
as a result of noninverting input bias current. At
useable voltage ranges at both the input and the
higher signal-supply voltages, these resistors should
output.
be increased in order to limit the added supply
current drawn through this path.
The circuit of Figure 37 shows the single-supply
ac-coupled, gain of +8V/V, video buffer circuit used
as the basis for the Electrical Characteristics table
and Typical Characteristics curves. The circuit of
Figure 37 establishes an input midpoint bias using a
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