Datasheet

R
F
+V
IN
R
G+
R
G-
-V
IN
FB
R
G
R
S
e
O
VCA820
*
e
O
i
n
4kTR
S
R
S
*
i
n
4kTR
S
NOTE:R andR arenoiseless.
F G
e =A ´
O VMAX
2 (R i ) +e +2 4kTR´ ´ ´
S n n S
2 2
+V
IN
R
G+
R
G-
-V
IN
FB
R
G
50W
10kW
1kW
50W
V
IN
VCA820
R
F
0.1 Fm
0.1 Fm
10kW
4kW
+5V
-5V
V
OUT
+5V
-5V
InputStageandMultiplexerCore
OffsetCompensationCircuit
OutputStageOffset
CompensationCircuit
VCA820
SBOS395C –OCTOBER 2007–REVISED OCTOBER 2009............................................................................................................................................ www.ti.com
NOISE
The VCA820 offers 8.2nV/√Hz input-referred voltage
noise density at a gain of 20dB and 1.8pA/√Hz
input-referred current noise density. The
input-referred voltage noise density considers that all
noise terms, except the input current noise but
including the thermal noise of both the feedback
resistor and the gain resistor, are expressed as one
term.
This model is formulated in Equation 5 and Figure 87.
(5)
Figure 87. Simple Noise Model
A more complete model is illustrated in Figure 89. For
additional information on this model and the actual
modeled noise terms, please contact the High-Speed
Product Application Support team at www.ti.com.
Figure 88. Adjusting the Input and Output Voltage Sources
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Product Folder Link(s): VCA820