AD509S データシートの表示（PDF） - Analog Devices
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AD509S Datasheet PDF : 4 Pages
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- ANALOGDEVICES fAX-ON-DEMAND HOTLINE
Page 15
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AD509
The O.lIlF cetatnic power supply bypass capacitors are
considerably more important for the AD509 than for low
frequency general purpose amplifiers. Their main purpose
is to convert the distributed high frequency ground to a
'lumped singJe point (the V+ point). The V+ to V- O.lIlF
capacitor equalizes the supply grounds while the O.lIlF
capacitor from V+ to signal ground should be returned to
signal common. The signal common, which is bypassed to
pin 7, is defined as that point at which the input signal
source, tltc feedback network, and tbe retUrn side of the load
are joined to the power common,
Note that the diagram shows each individual capacitor
directly connected to the appropriate terminal (pin 7 [V+).
[n addition, it is suggested that all connections be sbort and
direct, and as physically dose to the case as possible, so that
the length of any conducting path shared by external
components will be minimized.
.
COMPONENTS. Resistors are preferably metal fIlm types.
because they have less capacitance and stray inductance
than wire wound types, and are available with excellent
accuracies and temperatUre coefficients.
Diodes are hot carrier types for the very fastest-settling
applications, but lN914 types are suitable for more
routine uses.
Capacitors in critical locations are polystyrene, teflon, or
polycarbonate to minimize dielectric absorption.
CIRCUIT. For the fastest settling times, keep leads short,
INVERTING
INPUT
_INVERTING
INPUT
TO SIGNAL
COMMON POINT
OUTPUT
O O.,..F
CEIlAMIe OISe
B Figunt 5. Configuration for Unity Gain Applications
SO DYNAMIC RESPONSE OF ADS09
120
L ,100
30'
..! E 8'
T z'"
1800
~:i... <10
E ~ 20
orient components to minimize stray capacitance, keep
circuit impedance levels as low as consistent with the out-
put capabilities of the amplifier and the signal source,
reduce all extemalload capacitances to the absolute
minimum. Don't overlook sockets or printed circuit
board mounting as possible sources of dielectric absorption.
Avoid pole-zero mismatches in any feedback networks used
with the amplifier. Minimize noise pickup,
II
-20
.0
100
..
1011 1OOOt 1M
10M 100M
FREQUENCY-II,
-20.0
100
..
- 101< IOOIt
FREQUENCY H.
1M
10M 100M
Figure 6. Open Loop Frequency and Phase Response
Figure7. Open Loop Frequency Response for VariousCc's
THE ADS09 AS AN OUTPUT AMPLIFIER FOR FAST
CURRENT -OUTPUT D-TO-A CONVERTERS
Most fast integrated circuit digital to analog converters have
current outputs. That is, the digital input code is translated
to an output current proportional to the digital code. In
many applications, that output current is converted to a volt-
age by connecting an operational amplifier in the current-to-
voltage convc:;rsionmode. '
, The senling time of the combination depends on the settling
time of the DAC and the output amplifier. A good approxima-
tion is:
= Is TOTAL .JCt~DAC) 2 + ( ts AMP) 2
Figure 8 shows the AD509K connected as an output amplifier
with the ADS65K, high speed 12-bit IC digital-to-analog con-
verter. The 10 picofarad capacitor, Cl, compensates for the
2SpF AD56S output capacitance. The voltage output of the
AD565K/ADS09K combination settles to :to.Ol% in one
microsecond. The low input voltage drift and high open loop
gain of the ADSO9K assures 12-bit accuracy over the operating
temperature range.
AD566K
SkU
~
Some IC DACs settle to final output value in 100-500 nano-
seconds. Since most IC op amps require a longer time to settle
to :1:0.1%or :1:0.01%of final value, amplifier settling time can
dominate total settling time. And for a 12-bit DAC, one least
significant bit is only 0,024% of full-scale, so low drift and
high linearity and precision are also required of tbe output
amplifier.
Figure8. AD509 as an Output Amplifier for B Fast Current-
Output D-tO-AConvert",
-4-
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