Datasheet

OPA2694
SBOS320D − SEPTEMBER 2004 − REVISED APRIL 2013
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11
APPLICATION INFORMATION
WIDEBAND CURRENT FEEDBACK OPERATION
The OPA2694 provides exceptional AC performance for a
wideband, low-power, current-feedback operational
amplifier. Requiring only 5.8mA/ch quiescent current, the
OPA2694 offers a 690MHz bandwidth at a gain of +2,
along with a 1700V/μs slew rate. An improved output stage
provides ±70mA output drive, along with < 1.5V output
voltage headroom. This combination of low power and
high bandwidth can benefit high-resolution video
applications.
Figure 1 shows the DC-coupled, gain of +2, dual power-
supply circuit configuration used as the basis of the ±5V
Electrical Characteristic tables and Typical Characteristic
curves. For test purposes, the input impedance is set to
50Ω with a resistor to ground and the output impedance is
set to 50Ω with a series output resistor. Voltage swings
reported in the Electrical Charateristics are taken directly
at the input and output pins, while load powers (dBm) are
defined at a matched 50Ω load. For the circuit of Figure 1,
the total effective load will be 100Ω || 804Ω = 89Ω. One
optional component is included in Figure 1. In addition to
the usual power-supply decoupling capacitors to ground,
a 0.01μF capacitor is included between the two
power-supply pins. In practical PCB layouts, this optional
added capacitor will typically improve the 2nd-harmonic
distortion performance by 3dB to 6dB.
+5V
−
5V
−
V
S
+V
S
50
Ω
Load
50
Ω
50
Ω
V
O
V
I
50
Ω
Source
R
G
402
Ω
R
F
402
Ω
+
6.8
μ
F 0.1
μ
F
Optional
0.01
μ
F
1/2
OPA2694
+
6.8
μ
F0.1
μ
F
Figure 1. DC-Coupled, G = +2, Bipolar-Supply
Specification and Test Circuit
Figure 2 shows the DC-coupled, gain of −2V/V, dual
power-supply circuit used as the basis of the inverting
Typical Characteristic curves. Inverting operation offers
several performance benefits. Since there is no
common-mode signal across the input stage, the slew rate
for inverting operation is higher and the distortion
performance is slightly improved. An additional input
resistor, R
T
, is included in Figure 2 to set the input
impedance equal to 50Ω. The parallel combination of R
T
and R
G
sets the input impedance. Both the noninverting
and inverting applications of Figure 1 and Figure 2 will
benefit from optimizing the feedback resistor (R
F
) value for
bandwidth (see the discussion in Setting Resistor Values
to Optimize Bandwidth). The typical design sequence is to
select the R
F
value for best bandwidth, set R
G
for the gain,
then set R
T
for the desired input impedance. As the gain
increases for the inverting configuration, a point will be
reached where R
G
will equal 50Ω, where R
T
is removed
and the input match is set by R
G
only. With R
G
fixed to
achieve an input match to 50Ω, R
F
is simply increased, to
increase gain. This will, however, quickly reduce the
achievable bandwidth, as shown by the inverting gain of
–10 frequency response in the Typical Characteristic
curves. For gains > 10V/V (14dB at the matched load),
noninverting operation is recommended to maintain
broader bandwidth.
1/2
OPA2694
+5V
+V
S
−
V
S
−
5V
50
Ω
Load
50
Ω
20
Ω
R
T
66.5
Ω
R
G
200
Ω
+
6.8
μ
F0.1
μ
F
+
6.8
μ
F0.1
μ
F
Optional
0.01
μ
F
V
I
50
Ω
Source
R
F
402
Ω
V
O
Figure 2. DC-Coupled, G = −2V/V, Bipolar-Supply
Specification and Test Circuit