Datasheet

OPA694
+5V
+V
S
-V
S
-5V
50 LoadW
50W
20W
R
T
66.5W
R
G
200W
+
6.8 Fm0.1 Fm
+
6.8 Fm0.1 Fm
Optional
0.01 Fm
V
I
50 SourceW
R
F
402W
V
O
OPA694
+5V
+
-5V
-V
S
+V
S
50 LoadW
50W
50WV
O
V
I
50 SourceW
R
G
402W
RF
402W
+
6.8 Fm
0.1 Fm 6.8 Fm
0.1 Fm
0.1 Fm
OPA694
SBOS319G –SEPTEMBER 2004–REVISED JANUARY 2010 www.ti.com
APPLICATION INFORMATION
rate for inverting operation is higher and the distortion
performance is slightly improved. An additional input
WIDEBAND CURRENT FEEDBACK
resistor, R
T
, is included in Figure 32 to set the input
OPERATION
impedance equal to 50Ω. The parallel combination of
The OPA694 provides exceptional AC performance
R
T
and R
G
sets the input impedance. Both the
for a wideband, low-power, current-feedback
noninverting and inverting applications of Figure 31
operational amplifier. Requiring only 5.8mA quiescent
and Figure 32 will benefit from optimizing the
current, the OPA694 offers a 690MHz bandwidth at a
feedback resistor (R
F
) value for bandwidth (see the
gain of +2, along with a 1700V/ms slew rate. An
discussion in the Setting Resistor Values to Optimize
improved output stage provides ±80mA output drive,
Bandwidth section). The typical design sequence is to
along with < 1.5V output voltage headroom. This
select the R
F
value for best bandwidth, set R
G
for the
combination of low power and high bandwidth can
gain, then set R
T
for the desired input impedance. As
benefit high-resolution video applications.
the gain increases for the inverting configuration, a
point will be reached where R
G
will equal 50Ω, where
Figure 31 shows the DC-coupled, gain of +2, dual
R
T
is removed and the input match is set by R
G
only.
power-supply circuit configuration used as the basis
With R
G
fixed to achieve an input match to 50Ω, R
F
is
of the ±5V Electrical Characteristics table and Typical
simply increased, to increase gain. This will, however,
Characteristic curves. For test purposes, the input
quickly reduce the achievable bandwidth, as shown
impedance is set to 50Ω with a resistor to ground and
by the inverting gain of –10 frequency response in the
the output impedance is set to 50Ω with a series
Typical Characteristic curves. For gains > 10V/V
output resistor. Voltage swings reported in the
(14dB at the matched load), noninverting operation is
Electrical Characteristics are taken directly at the
recommended to maintain broader bandwidth.
input and output pins, while load powers (dBm) are
defined at a matched 50Ω load. For the circuit of
Figure 31, the total effective load will be 100Ω || 804Ω
= 89Ω. One optional component is included in
Figure 31. In addition to the usual power-supply
decoupling capacitors to ground, a 0.1mF capacitor is
included between the two power-supply pins. In
practical printed circuit board (PCB) layouts, this
optional added capacitor will typically improve the
2nd-harmonic distortion performance by 3dB to 6dB.
Figure 32. DC-Coupled, G = −2V/V,
Bipolar-Supply Specification and Test Circuit
ADC DRIVER
Figure 31. DC-Coupled, G = +2, Bipolar-Supply
Most modern, high-performance analog-to-digital
Specification and Test Circuit
converters (ADCs) require a low-noise, low-distortion
driver. The OPA694 combines low-voltage noise
(2.1nV/√Hz) with low harmonic distortion. See
Figure 32 shows the DC-coupled, gain of −2V/V, dual
Figure 33 for an example of a wideband, AC-coupled,
power-supply circuit used as the basis of the inverting
12-bit ADC driver.
Typical Characteristic curves. Inverting operation
offers several performance benefits. Since there is no
common-mode signal across the input stage, the slew
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Product Folder Link(s): OPA694