Datasheet

12
8
4
0
-4
-8
-12
Frequency(MHz)
20MHz,SECOND-ORDERBUTTERWORTH
LOW-PASSFREQUENCYRESPONSE
0.1 100101
Gain(dB)
600W
20MHz,Second-OrderButterworth
Low-PassFilter
1/2
OPA2673
+10V
Power-supply
decouplingnotshown.
32.3W 105W
5kW
5kW51W
V
I
0.1 Fm
402W
1/2
OPA2673
4V
I
100pF
133W
0.1 Fm
150pF
OPA2673
www.ti.com SBOS382F –JUNE 2008–REVISED MAY 2010
Where two outputs are switched (see Figure 77), the has been adjusted to optimize bandwidth for the
output line is always under the control of one amplifier itself. As the single-supply frequency
amplifier or the other as a result of the response plots show, the OPA2673 in this
make-before-break disable timing. In this case, the configuration gives greater than 400MHz small-signal
switching glitches for two 0V inputs drop to less than bandwidth. The capacitor values were chosen as low
20mV. as possible but adequate to override the parasitic
input capacitance of the amplifier. The resistor values
were slightly adjusted to give the desired filter
HIGH-SPEED ACTIVE FILTERS
frequency response while accounting for the
Wideband current-feedback op amps make ideal
approximate 1ns propagation delay through each
elements for implementing high-speed active filters
channel of the OPA2673.
where the amplifier is used as a fixed gain block
inside a passive RC circuit network. The relatively
HIGH-POWER TWISTED-PAIR DRIVER
constant bandwidth versus gain provides low
interaction between the actual filter poles and the A very demanding application for a high-speed
required gain for the amplifier. Figure 78 shows an amplifier is to drive a low load impedance while
example single-supply buffered filter application. In maintaining a high output voltage swing to high
this case, one of the OPA2673 channels is used to frequencies. Using the dual current-feedback op amp
set up the dc operating point and provide impedance OPA2673, an 8V
PP
output signal swing into a
isolation from the signal source into the second-stage twisted-pair line with a typical impedance of 50Ω can
filter. That stage is set up to implement a 20MHz, be realized. Configured as shown on the front page,
maximally flat Butterworth frequency response and the two amplifiers of the OPA2673 drive the output
provide an ac gain of +4V/V. transformer in a push-pull configuration, thus doubling
the peak-to-peak signal swing at each op amp output
The 51Ω input matching resistor is optional in this
to 8V
PP
. The transformer has a turns ratio of 1.4. The
case. The input signal is ac-coupled to the 5V dc
total load seen by the amplifier is 35Ω.
reference voltage developed through the resistor
divider from the +10V power supply. This first stage Line driver applications usually have a high demand
acts as a gain of +1V/V voltage buffer for the signal for transmitting the signal with low distortion.
where the 600Ω feedback resistor is required for Current-feedback amplifiers such as the OPA2673
stability. This first stage easily drives the low input are ideal for delivering low-distortion performance to
resistors required at the input of this high-frequency higher gains. The example shown is set for a
filter. The second stage is set for a dc gain of +1V/V, differential gain of 4V/V. This circuit can deliver the
carrying the 5V operating point through to the output maximum 8V
PP
signal with over 200MHz bandwidth.
pin, and an ac gain of +4V/V. The feedback resistor
Figure 78. Buffered Single-Supply Active Filter
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