Datasheet
DC LEVEL-SHIFTING
1/2
OPA2830
+5V
−
5V
V
O
50
Ω
V
IN
R
F
750
Ω
348
Ω
50
Ω
Source
150
Ω
R
G
750
Ω
6.8
µ
F
+
6.8
µ
F
+
0.1
µ
F
0.1
µ
F
0.01
µ
F
SINGLE-SUPPLY ADC INTERFACE
1/2
OPA2830
+V
S
V
OUT
V
IN
R
3
R
2
R
1
R
4
1/2
OPA2830
V
IN
750
Ω
562
Ω
2.26k
Ω
374
Ω
22pF
+3V
100
Ω
+3V
1/2
ADS5203
10−Bit
30MSPS
OPA2830
www.ti.com
.................................................................................................................................................. SBOS309D – AUGUST 2004 – REVISED AUGUST 2008
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 ( Δ 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 R
4
is between
200 Ω and 1.5k Ω .
• NG = G + V
OUT
/V
S
• R
1
= R
4
/G
• R
2
= R
4
/(NG – G)
• R
3
= R
4
/(NG – 1)
where:
• NG = 1 + R
4
/R
3
• 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.
Figure 72. DC-Coupled, G = +2, Bipolar Supply
Specification and Test Circuit
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.
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
Δ V
OUT
= 1.50V – G נ 0.25V = 1.00V. Plugging these
values into the above equations (with R
4
= 750 Ω )
gives: NG = 2.33, R
1
= 375 Ω , R
2
= 2.25k Ω , and R
3
=
563 Ω . The resistors were changed to the nearest
standard values for the circuit of Figure 73 .
Figure 73. DC-Coupled, +3V ADC Driver
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