Datasheet

OFFSET VOLTAGE
V
OO
+ V
IO
ǒ1 )
R
F
R
G
Ǔ" I
IB)
R
S
ǒ1 )
R
F
R
G
Ǔ" I
IB*
R
F
+
−
V
IO
+
R
G
R
S
R
F

I
IB− V
O
−

I
IB+
NOISE CALCULATIONS
_
+
R
F
R
S
R
G
e
Rg
e
Rf
e
Rs
e
n
IN+
Noiseless
IN−
e
ni
e
no
THS6184
www.ti.com ................................................................................................................................................. SLLS635D – AUGUST 2005 – REVISED JANUARY 2009
The output offset voltage, (V
OO
) is the sum of the input offset voltage (V
IO
) and both input bias currents (I
IB
) times
the corresponding gains. The following schematic and formula can be used to calculate the output offset voltage:
Figure 53. Output Offset Voltage Model
Noise can cause errors on very small signals. This is especially true for the amplifying small signals. The noise
model for current feedback amplifiers (CFB) is the same as voltage feedback amplifiers (VFB). The only
difference between the two is that the CFB amplifiers generally specify different current noise parameters for
each input while VFB amplifiers usually only specify one noise current parameter. The noise model is shown in
Figure 54 . This model includes all of the noise sources as follows:
• e
n
= Amplifier internal voltage noise (nV/ √ Hz)
• IN+ = Noninverting current noise (pA/ √ Hz)
• IN- = Inverting current noise (pA/ √ Hz)
• e
RX
= Thermal voltage noise associated with each resistor (e
RX
= √ 4 kTR
x
)
Figure 54. Noise Model
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