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參數資料
| 型號： | AD546 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 1 pA Monolithic Electrometer Operational Amplifier(單片靜電計運算放大器) |
| 中文描述： | 靜電計1功率放大器單片運算放大器（單片靜電計運算放大器） |
| 文件頁數： | 8/12頁 |
| 文件大?。?/td> | 465K |
| 代理商： | AD546 |
AD546
REV. A
–8–
Figure 28. Input Pin to Insulating Standoff
Leakage through the bulk of the circuit board will still occur
with the guarding schemes shown in Figures 27a and 27b. Stan-
dard “G10” type printed circuit board material may not have
high enough volume resistivity to hold leakages at the sub-
picoampere level particularly under high humidity conditions.
One option that eliminates all effects of board resistance
is shown in Figure 28. The AD546’s sensitive input pin (either
Pin 2 when connected as an inverter, or Pin 3 when connected
as a follower) is bent up and soldered directly to a Teflon* insu-
lated standoff. Both the signal input and feedback component
leads must also be insulated from the circuit board by Teflon
standoffs or low-leakage shielded cable.
Contaminants such as solder flux on the board’s surface and on
the amplifier’s package can greatly reduce the insulation resis-
tance between the input pin and those traces with supply or sig-
nal voltages. Both the package and the board must be kept clean
and dry. An effective cleaning procedure is to first swab the sur-
face with high grade isopropyl alcohol, then rinse it with deion-
ized water and, finally, bake it at 80
°
C for 1 hour. Note that if
either polystyrene or polypropylene capacitors are used on the
printed circuit board, a baking temperature of 70
°
C is safer,
since both of these plastic compounds begin to melt at approxi-
mately +85
°
C.
Other guidelines include making the circuit layout as compact
as possible and reducing the length of input lines. Keeping cir-
cuit board components rigid and minimizing vibration will re-
duce triboelectric and piezoelectric effects. All precision high
impedance circuitry requires shielding from electrical noise and
interference. For example, a ground plane should be used under
all high value (i.e., greater than 1 M
) feedback resistors. In
some cases, a shield placed over the resistors, or even the entire
amplifier, may be needed to minimize electrical interference
originating from other circuits. Referring to the equation in Fig-
ure 26, this coupling can take place in either, or both, of two
different forms—coupling via time varying fields:
dTC
P
or by injection of parasitic currents by changes in capacitance
due to mechanical vibration:
dTV
Both proper shielding and rigid mechanical mounting of compo-
nents help minimize error currents from both of these sources.
Table I lists various insulators and their properties.
Table I. Insulating Materials and Characteristics
Volume
Resistivity
(
V
–CM)
Minimal
Triboelectric
Effects
Minimal
Piezoelectric to Water
Effects
Resistance
Material
1
Absorption
Teflon*
Kel-F**
Sapphire
Polyethylene
Polystyrene
Ceramic
Glass Epoxy
PVC
Phenolic
10
17
–10
18
10
17
–10
18
10
16
–10
18
10
14
–10
18
10
12
–10
18
10
12
–10
14
10
10
–10
17
10
10
–10
15
10
5
–10
12
W
W
M
M
W
W
W
G
W
W
M
G
G
M
M
M
M
G
G
G
G
M
M
W
W
G
W
G–Good with Regard to Property.
M–Moderate with Regard to Property.
W–Weak with Regard to Property.
1
Electronic Measurements,
pp.15-17, Keithley Instruments, Inc., Cleveland,
Ohio, 1977.
*Teflon is a registered trademark of E.I. du Pont Co.
**Kel-F is a registered trademark of 3M Company.
OFFSET NULLING
The AD546’s input offset voltage can be nulled by using balance
Pins 1 and 5, as shown in Figure 29. Nulling the input offset
voltage in this fashion will introduce an added input offset volt-
age drift component of 2.4
μ
V/
°
C per millivolt of nulled offset.
Figure 29. Standard Offset Null Circuit
The circuit in Figure 30 can be used when the amplifier is used
as an inverter. This method introduces a small voltage in series
with the amplifier’s positive input terminal. The amplifier’s
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相關代理商/技術參數 |
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| AD546J | 制造商:AD 制造商全稱:Analog Devices 功能描述:1 pA Monolithic Electrometer Operational Amplifier |
| AD546JN | 制造商:AD 制造商全稱:Analog Devices 功能描述:1 pA Monolithic Electrometer Operational Amplifier |
| AD546K | 制造商:AD 制造商全稱:Analog Devices 功能描述:1 pA Monolithic Electrometer Operational Amplifier |
| AD546KN | 制造商:AD 制造商全稱:Analog Devices 功能描述:1 pA Monolithic Electrometer Operational Amplifier |
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