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參數(shù)資料
| 型號(hào)： | OP634 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | Wideband, Single-Supply Operational Amplifier(寬帶,單電源運(yùn)算放大器) |
| 中文描述： | 寬帶，單電源運(yùn)算放大器（寬帶，單電源運(yùn)算放大器） |
| 文件頁(yè)數(shù)： | 15/18頁(yè) |
| 文件大?。?/td> | 284K |
| 代理商： | OP634 |
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OPA634, OPA635
SBOS097A
15
The criterion for setting this R
S
resistor is a maximum
bandwidth, flat frequency response at the load. For a gain of
+2, the frequency response at the output pin is already
slightly peaked without the capacitive load, requiring rela-
tively high values of R
S
to flatten the response at the load.
Increasing the noise gain will also reduce the peaking (see
Figure 4).
DISTORTION PERFORMANCE
The OPA634 and OPA635 provide good distortion perfor-
mance into a 150
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 will dominate 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 non-inverting configuration
(Figure 1) 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 load.
NOISE PERFORMANCE
High slew rate, unity gain stable, voltage-feedback op amps
usually achieve their slew rate at the expense of a higher
input noise voltage. The 5.6nV/
√
Hz input voltage noise for
the OPA634 and OPA635 is, however, much 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 under a wide variety of
operating conditions. Figure 6 shows the op amp noise
analysis model with all the noise terms included. In this
model, all noise terms are taken to be noise voltage or
current density terms in either nV/
√
Hz or pA/
√
Hz.
The total output spot noise voltage can be computed as the
square root of the sum of all squared output noise voltage
contributors. Equation 1 shows the general form for the
output noise voltage using the terms shown in Figure 6:
(1)
E
O
=
E
NI
2
+
I
BN
R
S
(
)
2
+ 4
kTR
S
(
)
NG
2
+
I
BI
R
F
(
)
2
+ 4
kTR
F
NG
Dividing this expression by the noise gain (NG = (1 + R
F
/R
G
))
will give the equivalent input-referred spot noise voltage at
the non-inverting input, as shown in Equation 2:
(2)
E
N
=
E
NI
2
+
I
BN
R
S
(
)
2
+ 4
kTR
S
+
I
BI
R
F
NG
2
+4
kTR
F
NG
Evaluating these two equations for the circuit and compo-
nent values shown in Figure 1 will give a total output spot
noise voltage of 12.5nV/
√
Hz and a total equivalent input
spot noise voltage of 6.3nV/
√
Hz. This is including the noise
added by the resistors. This total input-referred spot noise
voltage is not much higher than the 5.6nV/
√
Hz specification
for the op amp voltage noise alone. This will be the case as
long as the impedances appearing at each op amp input are
limited to the previously recommend maximum value of
400
, and the input attenuation is low.
DC ACCURACY AND OFFSET CONTROL
The balanced input stage of a wideband voltage-feedback op
amp allows good output DC accuracy in a wide variety of
applications. The power-supply current trim for the OPA634
and OPA635 gives even tighter control than comparable
products. Although the high-speed input stage does require
relatively high input bias current (typically 25
μ
A out of each
input terminal), the close matching between them may be
used to reduce the output DC error caused by this current.
This is done by matching the DC source resistances appear-
ing at the two inputs. Evaluating the configuration of
Figure 1 (which has matched DC input resistances), using
worst-case +25
°
C input offset voltage and current specifica-
tions, gives a worst-case output offset voltage equal to:
(NG = non-inverting signal gain at DC)
±
(NG V
OS(MAX)
)
±
(R
F
I
OS(MAX)
)
=
±
(1 7.0mV)
±
(750
2.25
μ
A)
=
±
8.7mV
A fine scale output offset null, or DC operating point
adjustment, is often required. Numerous techniques are
available for introducing DC offset control into an op amp
circuit. Most of these techniques are based on adding a DC
current through the feedback resistor. In selecting an offset
trim method, one key consideration is the impact on the
desired signal path frequency response. If the signal path is
FIGURE 6. Noise Analysis Model.
4kT
R
G
R
G
R
F
R
S
OPA63x
I
BI
E
O
I
BN
4kT = 1.6E
–
20J
at 290
°
K
E
RS
E
NI
4kTR
S
√
4kTR
F
√
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