OPA2677 Datasheet, PDF (12/12 Pages) Burr-Brown (TI) – Dual, Wideband, High Output Current OPERATIONAL AMPLIFIER

APPLICATIONS INFORMATION
WIDEBAND CURRENT FEEDBACK OPERATION
The OPA2677 gives the exceptional AC performance of a
wideband current feedback op amp with a highly linear, high
power output stage. Requiring only 9mA/ch. quiescent cur-
rent, the OPA2677 will swing to within 1V of either supply
rail and deliver in excess of 380mA guaranteed at room
temperature. This low output headroom requirement, along
with supply voltage independent biasing, gives remarkable
single (+5V) supply operation. The OPA2677 will deliver
greater than 150MHz bandwidth driving a 2Vp-p output into
100Ω 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
OPA2677 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 +4, dual power
supply circuit configuration used as the basis of the ±6V
Specifications and Typical Performance 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 speci-
fications 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
|| 537Ω = 84Ω.
Figure 2 shows the AC coupled, gain of +4, 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 OPA2677 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 100MHz
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 806Ω resistors). The input signal is then AC coupled
into this midpoint voltage bias. The input voltage can swing
to within 1.3V of either supply pin, giving a 2.4Vp-p input
signal range centered between the supply pins. The input
impedance matching resistor (57.6Ω) used for testing is
adjusted to give a 50Ω 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 +1—which puts the input DC bias voltage (2.5V) on
the output as well. The feedback resistor value has been
adjusted from the bipolar supply condition to re-optimize for
a flat frequency response in +5V, gain of +4, operation.
Again, on a single +5V supply, the output voltage can swing
to within 1V of either supply pin while delivering more than
200mA output current. A demanding 100Ω load to a mid-
point bias is used in this characterization circuit. The new
output stage used in the OPA2677 can deliver large bipolar
output currents into this midpoint load with minimal cross-
over distortion, as shown by the +5V supply, harmonic
distortion plots.
+6V
0.1µF
+V_S
6.8µF
+
50Ω Source
V_I
50Ω
1/2
OPA2677
50Ω Load
V_O 50Ω
R_F
402Ω
R_G
133Ω
–V_S
–6V
6.8µF
0.1µF
+5V
+V_S
0.1µF
806Ω
+
0.1µF
6.8µF
V_I
57.6Ω 806Ω
1/2
V_O 100Ω
OPA2677
V_S/2
R_F
453Ω
R_G
150Ω
0.1µF
FIGURE 1. DC-Coupled, G = +4, Bipolar Supply, Specifi-
cation and Test Circuit.
FIGURE 2. AC-Coupled, G = +4, Single Supply Specifica-
tion and Test Circuit.
®
OPA2677
12