OPA682N BURR-BROWN [Burr-Brown Corporation], OPA682N Datasheet - Page 13

• Manufacturer Part Number: OPA682N
• Description: Wideband, Fixed Gain BUFFER AMPLIFIER With Disable
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

APPLICATIONS INFORMATION
WIDEBAND BUFFER OPERATION
The OPA682 gives the exceptional AC performance of a
wideband current feedback op amp with a highly linear, high
power output stage. It features internal R
which make it easy to select a gain of +2, +1 or –1 without
any external resistors. Requiring only 6mA quiescent cur-
rent, the OPA682 will swing to within 1V of either supply
rail and deliver in excess of 135mA guaranteed at room
temperature. This low output headroom requirement, along
with supply voltage independent biasing, gives remarkable
single (+5V) supply operation. The OPA682 will deliver
greater than 200MHz bandwidth driving a 2Vp-p output into
100 on a single +5V supply. Previous boosted output stage
amplifiers have typically suffered from very poor crossover
distortion as the output current goes through zero. The
OPA682 achieves a comparable power gain with much
better linearity. The primary advantage of a current feedback
op amp over a voltage feedback op amp is that AC perfor-
mance (bandwidth and distortion) is relatively independent
of signal gain.
Figure 1 shows the DC coupled, gain of +2, dual power
supply circuit configuration used as the basis of the 5V
Specifications and Typical Performance Curves. For test
purposes, the input impedance is set to 50
to ground and the output impedance is set to 50
series output resistor. Voltage swings reported in the speci-
fications are taken directly at the input and output pins while
load powers (dBm) are defined at a matched 50
the circuit of Figure 1, the total effective load will be 100
|| 800 = 89 . The disable control line (DIS) is typically left
open to guarantee normal amplifier operation. In addition to
the usual power supply decoupling capacitors to ground, a
0.1 F capacitor can be included between the two power
supply pins. This optional added capacitor will typically
improve the 2nd harmonic distortion performance by 3dB to
6dB.
FIGURE 1. DC-Coupled, G = +2, Bipolar Supply, Specifi-
50 Source
V
IN
50
cation and Test Circuit.
400
R
G
DIS
OPA682
400
R
F
+5V
–5V
0.1 F
0.1 F
F
and R
50
with a resistor
+
+
6.8 F
50 Load
6.8 F
G
load. For
resistors
with a
13
Figure 2 shows the AC coupled, gain of +2, single-supply
circuit configuration used as the basis of the +5V Specifica-
tions and Typical Performance Curves. Though not a “rail-
to-rail” design, the OPA682 requires minimal input and
output voltage headroom compared to other very wideband
current feedback op amps. It will deliver a 3Vp-p output
swing on a single +5V supply with greater than 150MHz
bandwidth. The key requirement of broadband single-supply
operation is to maintain input and output signal swings
within the usable voltage ranges at both the input and the
output. The circuit of Figure 2 establishes an input midpoint
bias using a simple resistive divider from the +5V supply
(two 806
into this midpoint voltage bias. The input voltage can swing
to within 1.5V of either supply pin, giving a 2Vp-p input
signal range centered between the supply pins. The input
impedance matching resistor (57.6 ) used for testing is
adjusted to give a 50
combination of the biasing divider network is included. The
gain resistor (R
gain of +1—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 more than 80mA output current. A demanding
100 load to a midpoint bias is used in this characterization
circuit. The new output stage used in the OPA682 can
deliver large bipolar output currents into this midpoint load
with minimal crossover distortion, as shown by the +5V
supply, 3rd harmonic distortion plots.
FIGURE 2. AC-Coupled, G = +2, Single Supply Specifica-
SINGLE-SUPPLY A/D CONVERTER INTERFACE
Most modern, high performance A/D converters (such as the
Burr-Brown ADS8xx and ADS9xx series) operate on a
single +5V (or lower) power supply. It has been a consider-
able challenge for single-supply op amps to deliver a low
distortion input signal at the ADC input for signal frequen-
V
50 Source
IN
57.6
0.1 F
resistors). The input signal is then AC-coupled
tion and Test Circuit.
G
806
806
) is AC-coupled, giving the circuit a DC
400
0.1 F
R
G
+V
input match when the parallel
S
OPA682
+5V
OPA682
400
R
F
0.1 F
V
O
+
DIS
6.8 F
100
V
S
/2
®