Datasheet
DISTORTION PERFORMANCE
4kT
R
G
R
G
R
F
R
S
1/4
OPA4830
I
BI
E
O
I
BN
4kT=1.6E 20J-
at290 K°
E
RS
E
NI
4kTR
S
4kTR
F
NOISE PERFORMANCE
E =
O
(E +(I R ) +4kTR )NG +(I R ) +4kTR NG
NI BN S BI FS F
2 2 2 2
E =
N
E +(I R ) +4kTR +
NI BN S S
2 2
I R
BI F
NG
2
+
4kTR
F
NG
OPA4830
SBOS350A – DECEMBER 2006 – REVISED MAY 2008 ....................................................................................................................................................
www.ti.com
The OPA4830 provides good distortion performance
into a 150 Ω load. Relative to alternative solutions, it
provides exceptional performance into lighter loads
and/or operating on a single +3V supply. Generally,
until the fundamental signal reaches very high
frequency or power levels, the 2nd-harmonic
dominates the distortion with a negligible
3rd-harmonic component. Focusing then on the
2nd-harmonic, increasing the load impedance
improves distortion directly. Remember that the total
load includes the feedback network; in the
noninverting configuration (see Figure 74 ) this is sum
of R
F
+ R
G
, while in the inverting configuration, only
R
F
needs to be included in parallel with the actual
Figure 89. Noise Analysis Model
load. Running differential suppresses the
2nd-harmonic, as shown in the Differential Typical
The total output spot noise voltage can be computed
Characteristics .
as the square root of the sum of all squared output
noise voltage contributors. Equation 8 shows the
general form for the output noise voltage using the
High slew rate, unity-gain stable, voltage-feedback op
terms shown in Figure 89 :
amps usually achieve their slew rate at the expense
of a higher input noise voltage. The 9.2nV/ √ Hz input
voltage noise for the OPA4830 however, is much
(8)
lower than comparable amplifiers. The input-referred
voltage noise and the two input-referred current noise
terms (2.8pA/ √ Hz) combine to give low output noise
Dividing this expression by the noise gain [ NG = (1 +
under a wide variety of operating conditions.
R
F
/R
G
) ] gives the equivalent input-referred spot noise
Figure 89 shows the op amp noise analysis model
voltage at the noninverting input; this result is shown
with all the noise terms included. In this model, all
in Equation 9 :
noise terms are taken to be noise voltage or current
density terms in either nV/ √ Hz or pA/ √ Hz.
(9)
Evaluating these two equations for the circuit and
component values shown in Figure 72 gives a total
output spot noise voltage of 19.3nV/ √ Hz and a total
equivalent input spot noise voltage of 9.65nV/ √ Hz.
This value is including the noise added by the
resistors. This total input-referred spot noise voltage
is not much higher than the 9.2nV/ √ Hz specification
for the op amp voltage noise alone.
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