ADA4817-1ACP-EBZ 查看數據表（PDF） - Analog Devices
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ADA4817-1ACP-EBZ Datasheet PDF : 28 Pages
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ADA4817-1/ADA4817-2
Data Sheet
THEORY OF OPERATION
The ADA4817-1/ADA4817-2 are voltage feedback operational
amplifiers that combine new architecture for FET input operational
amplifiers with the eXtra Fast Complementary Bipolar (XFCB)
process from Analog Devices, resulting in an outstanding
combination of speed and low noise. The innovative high speed
FET input stage handles common-mode signals from the negative
supply to within 2.7 V of the positive rail. This stage is combined
with an H-bridge to attain a 870 V/μs slew rate and low distortion,
in addition to 4 nV/√Hz input voltage noise. The amplifier
features a high speed output stage capable of driving heavy loads
sourcing and sinking up to 40 mA of linear current. Supply current
and offset current are laser trimmed for optimum performance.
These specifications make the ADA4817-1/ ADA4817-2 a great
choice for high speed instrumentation and high resolution data
acquisition systems. Its low noise, picoamp input current, precision
offset, and high speed make them superb preamps for fast photo-
diode applications.
CLOSED-LOOP FREQUENCY RESPONSE
The ADA4817-1/ADA4817-2 are classic voltage feedback
amplifiers with an open-loop frequency response that can be
approximated as the integrator response shown in Figure 43. Basic
closed-loop frequency response for inverting and noninverting
configurations can be derived from the schematics shown in
Figure 41 and Figure 42.
RF
RG
VIN
VE A
VOUT
Figure 41. Noninverting Configuration
RF
VIN
RG
VE A
VOUT
Figure 42. Inverting Configuration
NONINVERTING CLOSED-LOOP FREQUENCY
RESPONSE
Solving for the transfer function,
( ) VO =
2π × fCROSSOVER RG + RF
( ) VI RF + RG S + 2π × fCROSSOVER × RG
(4)
where fCROSSOVER is the frequency where the amplifier’s open-loop
gain equals 0 dB.
At dc,
VO = RF + RG
(5)
VI
RG
Closed-loop −3 dB frequency
f −3dB
=
f CROSSOVER
×
RG
RF + RG
(6)
INVERTING CLOSED-LOOP FREQUENCY RESPONSE
Solving for the transfer function,
( ) VO =
−2π × fCROSSOVER × RF
VI RF + RG S + 2π × fCROSSOVER × RG
(7)
At dc VO = − RF
(8)
VI
RG
Solve for closed-loop −3 dB frequency by,
f −3dB
=
f CROSSOVER
×
RG
RF + RG
(9)
80
A = (2π × fCROSSOVER)/s
60
40
20
fCROSSOVER = 410MHz
0
0.1
1
10
100
FREQUENCY (MHz)
1000
Figure 43. Open-Loop Gain vs. Frequency and Basic Connections
The closed-loop bandwidth is inversely proportional to the noise
gain of the op amp circuit, (RF + RG)/RG. This simple model is
accurate for noise gains above 2. The actual bandwidth of circuits
with noise gains at or below 2 is higher than those predicted
with this model due to the influence of other poles in the
frequency response of the real op amp.
Figure 44 shows a voltage feedback amplifier’s dc errors. For
both inverting and noninverting configurations,
VOUT
(error) = Ib+ × RS
RG +
RG
RF
− Ib− × RF
+
VOS
RG + RF
RG
(10)
RF
RG
+VOS –
RS
VIN
Ib– A
Ib+
VOUT
Rev. B | Page 14 of 28
Figure 44. Voltage Feedback Amplifier’s DC Errors
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