OPA2673 Datasheet, PDF (23/40 Pages) Texas Instruments – Dual, Wideband, High Output Current Operational Amplifier with Active Off-Line Control

OPA2673
www.ti.com..................................................................................................................................................... SBOS382A – JUNE 2008 – REVISED OCTOBER 2008
Where two outputs are switched (see Figure 77), the
output line is always under the control of one
amplifier or the other as a result of the
make-before-break disable timing. In this case, the
switching glitches for two 0V inputs drop to less than
20mV.
HIGH-SPEED ACTIVE FILTERS
Wideband current-feedback op amps make ideal
elements for implementing high-speed active filters
where the amplifier is used as a fixed gain block
inside a passive RC circuit network. The relatively
constant bandwidth versus gain provides low
interaction between the actual filter poles and the
required gain for the amplifier. Figure 78 shows an
example single-supply buffered filter application. In
this case, one of the OPA2673 channels is used to
set up the dc operating point and provide impedance
isolation from the signal source into the second-stage
filter. That stage is set up to implement a 20MHz,
maximally flat Butterworth frequency response and
provide an ac gain of +4V/V.
The 51Ω input matching resistor is optional in this
case. The input signal is ac-coupled to the 5V dc
reference voltage developed through the resistor
divider from the +10V power supply. This first stage
acts as a gain of +1V/V voltage buffer for the signal
where the 600Ω feedback resistor is required for
stability. This first stage easily drives the low input
resistors required at the input of this high-frequency
filter. The second stage is set for a dc gain of +1V/V,
carrying the 5V operating point through to the output
pin, and an ac gain of +4V/V. The feedback resistor
has been adjusted to optimize bandwidth for the
amplifier itself. As the single-supply frequency
response plots show, the OPA2673 in this
configuration gives greater than 400MHz small-signal
bandwidth. The capacitor values were chosen as low
as possible but adequate to override the parasitic
input capacitance of the amplifier. The resistor values
were slightly adjusted to give the desired filter
frequency response while accounting for the
approximate 1ns propagation delay through each
channel of the OPA2673.
HIGH-POWER TWISTED-PAIR DRIVER
A very demanding application for a high-speed
amplifier is to drive a low load impedance while
maintaining a high output voltage swing to high
frequencies. Using the dual current-feedback op amp
OPA2673, an 8V_PP output signal swing into a
twisted-pair line with a typical impedance of 50Ω can
be realized. Configured as shown on the front page,
the two amplifiers of the OPA2673 drive the output
transformer in a push-pull configuration, thus doubling
the peak-to-peak signal swing at each op amp output
to 8V_PP. The transformer has a turns ratio of 1.4. The
total load seen by the amplifier is 35Ω.
Line driver applications usually have a high demand
for transmitting the signal with low distortion.
Current-feedback amplifiers such as the OPA2673
are ideal for delivering low-distortion performance to
higher gains. The example shown is set for a
differential gain of 4V/V. This circuit can deliver the
maximum 8V_PP signal with over 200MHz bandwidth.
+10V
Power-supply
decoupling not shown.
5kW
0.1mF
V_I
51W
5kW
1/2
OPA2673
32.3W
100pF
105W
150pF
1/2
OPA2673
4V_I
600W
40W
20MHz, Second-Order Butterworth
Low-Pass Filter
133W
0.1mF
12
8
4
0
-4
-8
-12
0.1
20MHz, SECOND-ORDER BUTTERWORTH
LOW-PASS FREQUENCY RESPONSE
1
10
100
Frequency (MHz)
Figure 78. Buffered Single-Supply Active Filter
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): OPA2673
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