Datasheet
DC LEVEL-SHIFTING
NG=G+V /V
R =R /G
R =R /(NG G)
R =R /(NG 1)
OUT S
1 4
2
3
4
4
-
-
(1)
NG=1+R /R
V =(G)V +(NG G)V
4 3
OUT IN S
-
(2)
1/4
OPA4830
+V
S
V
OUT
V
IN
R
3
R
2
R
1
R
4
1/4
OPA4830
+5V
-5V
V
O
50W
V
IN
R
F
750W
348W
50 SourceW
150W
R
G
750W
6.8 Fm
+
6.8 Fm
+
0.1 Fm
0.1 Fm
0.01 Fm
OPA4830
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.................................................................................................................................................... SBOS350A – DECEMBER 2006 – REVISED MAY 2008
Figure 74 illustrates the dc-coupled, gain of +2V/V,
dual power-supply circuit configuration used as the
Figure 75 shows a DC-coupled noninverting amplifier
basis of the ± 5V Electrical Characteristics and Typical
that level-shifts the input up to accommodate the
Characteristics . For test purposes, the input
desired output voltage range. Given the desired
impedance is set to 50 Ω with a resistor to ground and
signal gain (G), and the amount V
OUT
needs to be
the output impedance is set to 150 Ω with a series
shifted up ( Δ V
OUT
) when V
IN
is at the center of its
output resistor. Voltage swings reported in the
range, Equation 1 and Equation 2 give the resistor
specifications are taken directly at the input and
values that produce the desired performance.
output pins. For the circuit of Figure 74 , the total
Assume that R
4
is between 200 Ω and 1.5k Ω .
effective load is 150 Ω 1.5k Ω . Two optional
components are included in Figure 74 . An additional
resistor (348 Ω ) is included in series with the
noninverting input. Combined with the 25 Ω dc source
resistance looking back towards the signal generator,
this gives an input bias current cancelling resistance
that matches the 375 Ω source resistance seen at the
where:
inverting input (see the DC Accuracy and Offset
Control section). In addition to the usual power-supply
decoupling capacitors to ground, a 0.01 µ F capacitor
is included between the two power-supply pins. In
Make sure that V
IN
and V
OUT
stay within the specified
practical printed circuit board layouts, this optional
input and output voltage ranges.
capacitor typically improves the 2nd-harmonic
distortion performance by 3dB to 6dB.
Figure 75. DC Level-Shifting
The circuit on the front page 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
Figure 74. DC-Coupled, G = +2V/V, Bipolar Supply
and 2V when using a +3V supply. This output means
Specification and Test Circuit
G = 2.00, and Δ V
OUT
= 1.50V – G × 0.25V = 1.00V.
Plugging these values into Equation 1 and Equation 2
(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 front page
circuit .
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