AD707JR-REEL7 Ver la hoja de datos (PDF) - Analog Devices

Número de pieza

componentes Descripción

Fabricante

AD707JR-REEL7

Ultralow Drift Op Amp

Analog Devices 

AD707

OFFSET NULLING

The input offset voltage of the AD707 is the lowest available in

a bipolar op amp, but if additional nulling is required, the

circuit shown in Figure 19 offers a null range of 200 µV. For

wider null capability, omit R1 and substitute a 20 kΩ potenti-

ometer for R2.

OPERATION WITH A GAIN OF 100

Demonstrating the outstanding dc precision of the AD707 in

practical applications, Table I shows an error budget calculation

for the gain of –100 configuration shown in Figure 21.

Table I. Error Budget

+VS

0.1µF

R1

10kΩ

OFFSET

ADJUST

Error Source

Maximum Error Contribution

Av = 100 (C Grade)

(Full Scale: VOUT = 10 V, VIN = 100 mV)

7

2

R2

1 2kΩ

VOS

15 µV/100 mV

= 150 ppm

IOS

(100 Ω)(1 nA)/100 mV = 1 ppm

OBSOLETE 8

AD707

6

3

4 0.1µF

–VS

Figure 19. External Offset Nulling and Power Supply

Bypassing

GAIN LINEARITY INTO A 1 kΩ LOAD

The gain and gain linearity of the AD707 are the highest

available among monolithic bipolar amplifiers. Unlike other dc

precision amplifiers, the AD707 shows no degradation in gain or

gain linearity when driving loads in excess of 1 kΩ over a ± 10 V

output swing. This means high gain accuracy is assured over the

output range. Figure 20 shows the gain of the AD707, OP07, and

the OP77 amplifiers when driving a 1 kΩ load.

The AD707 will drive 10 mA of output current with no signifi-

cant effect on its gain or linearity.

Gain (2 kΩ Load) (100 V/8 × 106)100 mV

Noise

0.35 µV/100 mV

VOS Drift

(0.1 V/°C)/100 mV

= 13 ppm

= 4 ppm

= 1 ppm/°C

= 168 ppm

+1 ppm/°C

Total Unadjusted Error

@ +25°C

@ –55°C to +125°C

With Offset Calibrated Out

@ +25°C

@ –55°C to +125°C

= 168 ppm > 12 Bits

= 268 ppm > 11 Bits

= 17 ppm > 15 Bits

= 117 ppm > 13 Bits

100Ω

VIN

10kΩ

+VS 0.1µF

2

7

AD707

6

VOUT

AD707

3

99Ω

4

0.1µF

–VS

OP07

OP77

@ +25°C

RLOAD = 1kΩ

–15

–10

–5

0

5

10

15

OUTPUT VOLTAGE – V

Figure 20. Gain Linearity of the AD707 vs.

Other DC Precision Op Amps

Figure 21. Gain of –100 Configuration

Although the initial offset voltage of the AD707 is very low, it is

nonetheless the major contributor to system error. In cases

requiring additional accuracy, the circuit shown in Figure 19

can be used to null out the initial offset voltage. This method

will also cancel the effects of input offset current error. With the

offsets nulled, the AD707C will add less than 17 ppm of error.

This error budget assumes no error in the resistor ratio and no

errors from power supply variation (the 120 dB minimum PSRR

of the AD707C makes this a good assumption). The external

resistors can cause gain error from mismatch and drift over

temperature.

–6–

REV. B

Share Link: