OPA2690 Datasheet, PDF (13/30 Pages) Burr-Brown (TI) – Dual, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable

OPA2690
www.ti.com
APPLICATIONS INFORMATION
WIDEBAND VOLTAGE-FEEDBACK OPERATION
The OPA2690 provides an exceptional combination of
high output power capability in a dual, wideband,
unity-gain stable, voltage-feedback op amp using a new
high slew rate input stage. Typical differential input stages
used for voltage-feedback op amps are designed to steer
a fixed-bias current to the compensation capacitor, setting
a limit to the achievable slew rate. The OPA2690 uses a
new input stage which places the transconductance
element between two input buffers, using their output
currents as the forward signal. As the error voltage
increases across the two inputs, an increasing current is
delivered to the compensation capacitor. This provides
very high slew rate (1800V/µs) while consuming relatively
low quiescent current (5.5mA/ch). This exceptional
full-power performance comes at the price of a slightly
higher input noise voltage than alternative architectures.
The 5.5nV/√Hz input voltage noise for the OPA2690 is
exceptionally low for this type of input stage.
Figure 1 shows the DC-coupled, gain of +2, dual power-
supply circuit configuration used as the basis of the ±5V
Electrical Characteristics and Typical Characteristics.
This is for one channel; the other channel is connected
similarly. 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 characteristics are taken directly
at the input and output pins, while output powers (dBm)
are at the matched 50Ω load. For the circuit of Figure 1, the
total effective load will be 100Ω 804Ω. The disable
control line (SO-14 package only) is typically left open for
normal amplifier operation. Two optional components are
included in Figure 1. An additional resistor (175Ω) is
included in series with the noninverting input. Combined
with the 25Ω DC source resistance looking back towards
the signal generator, this gives an input bias current
cancelling resistance that matches the 200Ω source
resistance seen at the inverting input (see the DC
Accuracy and Offset Control section). In addition to the
usual power-supply decoupling capacitors to ground, a
0.1µF capacitor is included between the two power-supply
pins. In practical PC board layouts, this optional-added
capacitor will typically improve the 2nd-harmonic
distortion performance by 3dB to 6dB.
Figure 2 shows the AC-coupled, gain of +2, single-supply
circuit configuration used as the basis of the +5V Electrical
and Typical Characteristics. Though not a rail-to-rail
design, the OPA2690 requires minimal input and output
voltage headroom compared to other very wideband
voltage-feedback op amps. It will deliver a 3V_PP output
swing on a single +5V supply with > 150MHz bandwidth.
The key requirement of broadband single-supply
operation is to maintain input and output signal swings
SBOS238D − JUNE 2002 − REVISED DECEMBER 2004
within the useable 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 698Ω resistors). Separate bias networks
would be required at each input. The input signal is then
AC-coupled into the midpoint voltage bias. The input
voltage can swing to within 1.5V of either supply pin, giving
a 2V_PP input signal range centered between the supply
pins. The input impedance matching resistor (59Ω) used
for testing is adjusted to give a 50Ω input load when the
parallel combination of the biasing divider network is
included.
+5V
+V_S
0.1µ F
6.8µ F
+
50Ω Source
175Ω
V_I
50Ω
V_D
1/2
OPA2690
DIS
50Ω Load
V_O 50Ω
0.1µF
R_F
402Ω
R_G
402Ω
− V_S
−5V
6.8µ F
0.1µF
Figure 1. DC-Coupled, G = +2, Bipolar Supply,
Specification and Test Circuit
+5V
+V_S
698Ω
0.1µF 6.8µF
0.1µ F
50Ω
DIS
V_I
59Ω
698Ω
V_D
1/2
OPA2690
V_O 100Ω
V_S/2
R_F
402Ω
R_G
402Ω
0.1µF
Figure 2. DC-Coupled, G = +2, Single-Supply,
Specification and Test Circuit
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