AD623
APPLICATIONS INFORMATION
The input voltage, which can be either single-ended (tie either
−IN or +IN to ground), or differential is amplified by the
programmed gain. The output signal appears as the voltage
difference between the OUTPUT pin and the externally applied
voltage on the REF input. For a ground-referenced output, REF
should be grounded.
BASIC CONNECTION
Figure 42 and Figure 43 show the basic connection circuits for
the AD623. The +VS and −VS terminals are connected to the
power supply. The supply can be either bipolar (VS = 2.5 V to
6 V) or single supply (−VS = 0 V, +VS = 3.0 V to 12 V). Power
supplies should be capacitively decoupled close to the power pins of
the device. For the best results, use surface-mount 0.1 μF ceramic
chip capacitors and 10 μF electrolytic tantalum capacitors.
GAIN SELECTION
The gain of the AD623 is resistor programmed by RG, or more
precisely, by whatever impedance appears between Pin 1 and
Pin 8. The AD623 is designed to offer accurate gains using 0.1%
to 1% tolerance resistors. Table 5 shows the required values of
RG for the various gains. Note that for G = 1, the RG terminals
are unconnected (RG = ∞). For any arbitrary gain, RG can be
calculated by
+V
S
0.1µF
10µF
+2.5V TO +6V
R
G
V
V
R
OUTPUT
REF
OUT
IN
G
R
G
REF (INPUT)
RG = 100 kΩ/(G − 1)
0.1µF
10µF
REFERENCE TERMINAL
–V
S
–2.5V TO –6V
The reference terminal potential defines the zero output voltage
and is especially useful when the load does not share a precise
ground with the rest of the system. It provides a direct means of
injecting a precise offset to the output. The reference terminal is
also useful when bipolar signals are being amplified because it
can be used to provide a virtual ground voltage. The voltage on
the reference terminal can be varied from −VS to +VS.
Figure 42. Dual-Supply Basic Connection
+V
S
0.1µF
10µF
+3V TO +12V
R
R
G
V
V
R
OUTPUT
REF
OUT
IN
G
G
REF (INPUT)
Figure 43. Single-Supply Basic Connection
Table 5. Required Values of Gain Resistors
Desired Gain
1% Standard Table Value of RG (Ω)
100 k
Calculated Gain Using 1% Resistors
2
2
5
10
20
33
40
50
65
100
200
500
1000
24.9 k
11 k
5.02
10.09
20.12
33.36
40.21
49.78
64.29
99.04
201.4
501
5.23 k
3.09 k
2.55 k
2.05 k
1.58 k
1.02 k
499
200
100
1001
Rev. D | Page 16 of 24
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