OPA2830_08 Datasheet, PDF (24/41 Pages) Burr-Brown (TI) – Dual, Low-Power, Single-Supply, Wideband OPERATIONAL AMPLIFIER

OPA2830
SBOS309C – AUGUST 2004 – REVISED MARCH 2006
50Ω Source
V_IN
348Ω
50Ω
+5V
0.1µF
6.8µF
+
1/2
OPA2830
V_O
150Ω
0.01µF
R_F
750Ω
R_G
750Ω
6.8µF
+
0.1µF
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voltage range. Given the desired signal gain (G), and
the amount V_OUT needs to be shifted up (∆V_OUT)
when V_IN is at the center of its range, the following
equations give the resistor values that produce the
desired performance. Assume that R₄ is between
200Ω and 1.5kΩ.
• NG = G + V_OUT/V_S
• R₁ = R₄/G
• R₂ = R₄/(NG – G)
• R₃ = R₄/(NG – 1)
where:
• NG = 1 + R₄/R₃
• V_OUT = (G)V_IN + (NG – G)V_S
Make sure that V_IN and V_OUT stay within the specified
input and output voltage ranges.
−5V
Figure 72. DC-Coupled, G = +2, Bipolar Supply
Specification and Test Circuit
SINGLE-SUPPLY ADC INTERFACE
The ADC interface of Figure 73 shows a
DC-coupled, single-supply ADC driver circuit. Many
systems are now requiring +3V to +5V supply
capability of both the ADC and its driver. The
OPA2830 provides excellent performance in this
demanding application. Its large input and output
voltage ranges and low distortion support converters
such as the ADS5203 shown in the figure on page 1.
The input level-shifting circuitry was designed so that
V_IN can be between 0V and 0.5V, while delivering an
output voltage of 1V to 2V for the ADS5203.
+3V
2.26kΩ
374Ω
V_IN
1/2
O P A 2 8 30
562Ω
750Ω
100Ω
22pF
+3V
1/2
ADS5203
10−Bit
30MSPS
Figure 73. DC-Coupled, +3V ADC Driver
DC LEVEL-SHIFTING
Figure 74 shows the general form of Figure 73 as a
DC-coupled noninverting amplifier that level-shifts
the input up to accommodate the desired output
R₁
V_IN
+V_S
R₂
1/2
OPA2830
V_OUT
R₃
R₄
Figure 74. DC Level-Shifting
The circuit of Figure 73 is a good example of this
type of application. It was designed to take V_IN
between 0V and 0.5V and produce V_OUT between 1V
and 2V when using a +3V supply. This means G =
2.00, and ∆V_OUT = 1.50V – G × 0.25V = 1.00V.
Plugging these values into the above equations (with
R₄ = 750Ω) gives: NG = 2.33, R₁ = 375Ω, R₂ =
2.25kΩ, and R₃ = 563Ω. The resistors were changed
to the nearest standard values for the circuit of
Figure 73.
AC-COUPLED OUTPUT VIDEO LINE DRIVER
Low-power and low-cost video line drivers often
buffer digital-to-analog converter (DAC) outputs with
a gain of 2 into a doubly-terminated line. Those
interfaces typically require a DC blocking capacitor.
For a simple solution, that interface often has used a
very large value blocking capacitor (220µF) to limit
tilt, or SAG, across the frames. One approach to
creating a very low high-pass pole location using
much lower capacitor values is shown in Figure 76.
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