OPA4830 Datasheet, PDF (27/45 Pages) National Semiconductor (TI) – Quad, Low-Power, Single-Supply, Wideband Operational Amplifier

OPA4830
www.ti.com.................................................................................................................................................... SBOS350A – DECEMBER 2006 – REVISED MAY 2008
DC-COUPLED SINGLE-TO-DIFFERENTIAL
CONVERSION
The previous differential output circuits were set up to
receive a differential input as well as provide a
differential output. Figure 82 illustrates one way to
provide a single-to-differential conversion, with dc
coupling, and independent output common-mode
control using a quad op amp.
The circuit of Figure 82 provides several useful
features for isolating the input signal from the final
outputs. Using the first amplifier as a simple
noninverting stage gives an independent adjustment
on R_I (to set the source loading) while the gain can
be easily adjusting in this stage using the R_G resistor.
The next stage allows a separate output
common-mode level to be set up. The desired output
common-mode voltage, V_CM, is cut in half and applied
to the noninverting input of the second stage. The
signal path in this stage sees a gain of –1V/V while
this (1/2 × V_CM) voltage sees a gain of +2V/V. The
output of this second stage is then the original
common-mode voltage plus the inverted signal from
the output of the first stage. The 2nd stage output
appears directly at the output of the noninverting final
stage. The inverting node of the inverting output
stage is also biased to the common-mode voltage,
equal to the common-mode voltage appearing at the
output of the second stage, creating no current flow
and placing the desired V_CM at the output of this
stage as well.
V_I
R_I
1/4
OPA4830
0.1mF
+5V
1.5V
V_CM
200W
750W _VCM
2
750W
1/4
OPA4830
402W
1/4
OPA4830
402W
+V_OUT
=
V_CM
+
V_I (1
+
402W
R_G
)
402W
R_G
750W
750W
50W
200W
1/4
OPA4830
250W
-V_OUT
=
V_CM
-
V_I (1
+
402W
R_G
)
-5V
Figure 82. Wideband, DC-Coupled, Single-to-Differential Conversion
Copyright © 2006–2008, Texas Instruments Incorporated
Product Folder Link(s): OPA4830
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