OPA2830 Datasheet, PDF (23/43 Pages) National Semiconductor (TI) – Dual, Low-Power, Single-Supply, Wideband OPERATIONAL AMPLIFIER

OPA2830
www.ti.com.................................................................................................................................................. SBOS309D – AUGUST 2004 – REVISED AUGUST 2008
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
+
−5V
0.1µF
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.
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 voltage
range. Given the desired signal gain (G), and the
amount V_OUT needs to be shifted up (ΔV_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.
R₁
V_IN
+V_S
R₂
1/2
OPA2830
V_OUT
R₃
R₄
+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
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
ΔV_OUT = 1.50V – G נ0.25V = 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.
Copyright © 2004–2008, Texas Instruments Incorporated
Product Folder Link(s): OPA2830
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