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AD623

Rev. D | Page 16 of 24

APPLICATIONS INFORMATION

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.

VIN

OUTPUT

VOUT

REF

REF (INPUT)

+2.5V TO +6V

+VS

10µF

0.1µF

–2.5V TO –6V

–VS

10µF

0.1µF

Figure 42. Dual-Supply Basic Connection

VIN

OUTPUT

VOUT

REF

REF (INPUT)

+3V TO +12V

+VS

10µF

0.1µF

Figure 43. Single-Supply Basic Connection

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.

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

= 100 kΩ/(G − 1)

REFERENCE TERMINAL

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.

Table 5. Required Values of Gain Resistors

Desired Gain

1% Standard Table Value of RG (Ω)

Calculated Gain Using 1% Resistors

100 k

24.9 k

5.02

11 k

10.09

5.23 k

20.12

3.09 k

33.36

2.55 k

40.21

2.05 k

49.78

1.58 k

64.29

100

1.02 k

99.04

200

499

201.4

500

200

501

1000

100

1001

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