AD795KN データシートの表示（PDF） - Analog Devices
部品番号
コンポーネント説明
メーカー
AD795KN Datasheet PDF : 16 Pages
| |||
AD795
10µV
is & if
SIGNAL BANDWIDTH
1µV
in
WITH FILTER
NO FILTER
100nV
en
en
10nV
1
10
100
1k
10k
100k
FREQUENCY – Hz
Figure 46. Voltage Noise Spectral Density of the Circuit of
Figure 45 With and Without an Output Filter
10pF
RG
10kΩ
Rf
108 Ω
Ri
1.1kΩ
PHOTODIODE
AD795
VOUT
VOUT
=
I D Rf
(1+
RG
Ri
)
Figure 47. A Photodiode Preamp Employing a “T”
Network for Added Gain
Using a “T” Network
A “T” network, shown in Figure 47, can be used to boost the
effective transimpedance of an I-to-V converter, for a given
feedback resistor value. However, amplifier noise and offset
voltage contributions are also amplified by the “T” network
gain. A low noise, low offset voltage amplifier, such as the
AD795, is needed for this type of application.
A pH Probe Buffer Amplifier
A typical pH probe requires a buffer amplifier to isolate its 106
to 109 Ω source resistance from external circuitry. Just such an
amplifier is shown in Figure 48. The low input current of the
AD795 allows the voltage error produced by the bias current
and electrode resistance to be minimal. The use of guarding,
shielding, high insulation resistance standoffs, and other such
standard methods used to minimize leakage are all needed to
maintain the accuracy of this circuit.
The slope of the pH probe transfer function, 50 mV per pH
unit at room temperature, has a +3300 ppm/°C temperature
coefficient. The buffer of Figure 48 provides an output voltage
equal to 1 volt/pH unit. Temperature compensation is provided
by resistor RT which is a special temperature compensation
resistor, part number Q81, 1 kΩ, 1%, +3500 ppm/°C, available
from Tel Labs Inc.
PH
PROBE
GUARD
V OS ADJUST
100kΩ
–VS
1
4
3
5
AD795
2
7
8
+VS
+VS
+15V
0.1µF
COM
0.1µF
–VS
–15V
OUTPUT
6
1VOLT/pH UNIT
19.6kΩ
RT
1kΩ
+3500ppm/ °C
Figure 48. A pH Probe Amplifier
–14–
REV. A
Share Link: 