Datasheet

OPA835
Signal and bias to
next stage
Signal and bias
from previous stage
2.5 V
2.5 V
5 V
R
1
R ’
G
R ”
G
R
F
R
O
V
OUT
GV
SIG
5 V
V
SIG
OPA835
Signal and bias to
next stage
Signal and bias
from previous stage
C
V
SIG
2.5 V
R
1
R
G
5 V
R
F
R
O
2.5 V
V
OUT
GV
SIG
5 V
2.5 V
REF
OPA835
OPA2835
SLOS713E –JANUARY 2011–REVISED JULY 2013 www.ti.com
Figure 63. Non-Inverting Single Supply with Reference
Figure 64 shows a similar non-inverting single supply scenario with the reference generator replaced by the
Thevenin equivalent using resistors and the positive supply. R
G
’ and R
G
” form a resistor divider from the 5V
supply and are used to bias the negative side with their parallel sum equal to the equivalent R
G
to set the gain.
To cancel the voltage offset that would otherwise be caused by the input bias currents, R
1
in is chosen to be
equal to R
F
in parallel with R
G
’ in parallel with R
G
” (R
1
= R
F
||R
G
’||R
G
”). For example if gain of 2 is required and R
F
= 2 kΩ, selecting R
G
’ = R
G
” = 4 kΩ gives equivalent parallel sum of 2 kΩ, sets the gain to 2, and references the
input to mid supply (2.5 V). R
1
is then set to 1kΩ for bias current cancellation. This can be lower cost, but note
the extra current draw required in the resistor divider.
Figure 64. Non-Inverting Single Supply with Resistors
Figure 65 shows a typical inverting amplifier situation. With 5V single supply, a mid supply reference generator is
needed to bias the positive side via R
1
. To cancel the voltage offset that would otherwise be caused by the input
bias currents, R
1
is chosen to be equal to R
F
in parallel with R
G
. For example if gain of -2 is required and R
F
= 2
kΩ, select R
G
= 1 kΩ to set the gain and R
1
= 665 Ω for bias current cancellation. The value for C is dependent
on the reference, but at least 0.1µF is recommended to limit noise into the op amp.
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