參數(shù)資料
型號(hào): OPA2674
英文描述: Dual Wideband, High Output Current Operational Amplifier with Current Limit
中文描述: 雙寬帶,高輸出電流運(yùn)算放大器,具有電流限制
文件頁數(shù): 17/30頁
文件大小: 472K
代理商: OPA2674
"#$%
SBOS270 AUGUST 2003
www.ti.com
17
1/2
OPA2674
+5V
+V
S
V
S
/2
806
100
V
O
V
I
57.6
806
R
F
453
R
G
150
0.1
μ
F
0.1
μ
F
6.8
μ
F
+
0.1
μ
F
Figure 3. AC-Coupled, G = +4, Single-Supply,
Specification and Test Circuit
The last configuration used as the basis of the +5V
Electrical and Typical Characteristics is shown in Figure 4.
Design considerations for this inverting, bipolar supply
configuration are covered either in single-supply
configuration (as shown in Figure 3) or in the Inverting
Amplifier Operation discussion.
1/2
OPA2674
+5V
V
S
/2
806
V
I
100
V
O
806
R
F
453
R
88.7
6.8
μ
F
+
0.1
μ
F
0.1
μ
F
R
G
113
Figure 4. AC-Coupled, G = 4, Single-Supply,
Specification and Test Circuit
SINGLE-SUPPLY ADSL UPSTREAM DRIVER
Figure 5 shows a single-supply ADSL upstream driver.
The dual OPA2674 is configured as a differential gain
stage to provide signal drive to the primary of the
transformer (here, a step-up transformer with a turns ratio
of 1:1.7). The main advantage of this configuration is the
reduction of even-order harmonic distortion products.
Another important advantage for ADSL is that each
amplifier needs only half of the total output swing required
to drive the load.
R
82.5
2k
2k
1
μ
F
0.1
μ
F
0.1
μ
F
17.4
R
M
100
AFE
2V
PP
Max
Assumed
R
F
324
20
20
R
F
324
1/2
OPA2674
1/2
OPA2674
+12V
1:1.7
17.7V
PP
I
P
= 128mA
I
P
= 128mA
17.4
R
M
+6V
Z
Line
Figure 5. Single-Supply ADSL Upstream Driver
The analog front-end (AFE) signal is AC-coupled to the
driver and the noninverting input of each amplifier is biased
to the mid-supply voltage (in this case, +6V). Furthermore,
by providing the proper biasing to the amplifier, this
scheme also provides high-pass filtering with a corner
frequency set here at 5kHz. As the upstream signal
bandwidth starts at 26kHz, this high-pass filter does not
generate any problems and has the advantage of filtering
out unwanted lower frequencies.
The input signal is amplified with a gain set by the following
equation:
G
D
1
2
R
F
R
G
With R
F
= 324
and R
G
= 82.5
, the gain for this
differential amplifier is 8.85. This gain boosts the AFE
signal, assumed to be a maximum of 2V
PP
, to a maximum
of 17.7V
PP
.
Refer to the Setting Resistor Values to Optimize
Bandwidth section for a discussion on which feedback
resistor value to choose.
The two back-termination resistors (17.4
each) added at
each input of the transformer make the impedance of the
modem match the impedance of the phone line, and also
provide a means of detecting the received signal for the
receiver. The value of these resistors (R
M
) is a function of
the line impedance and the transformer turns ratio (n),
given by the following equation:
R
M
Z
LINE
2n
2
(1)
(2)
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