AD820BN View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

AD820BN

Single Supply, Rail to Rail Low Power FET-Input Op Amp

Analog Devices 

Prev 11 12 13 14 15 16

R1

100k⍀

R2

100k⍀

+VS

+VS

0.01␮F

A

0.01␮F

37

7

3

6

C

VIN

6

A1

2

A2

2

4 AD820

FULL-WAVE

RECTIFIED OUTPUT

4 AD820

B

HALF-WAVE

RECTIFIED OUTPUT

A

B

C

Figure 44. Single Supply Half- and Full-Wave Rectifier

4.5 Volt Low Dropout, Low Power Reference

The rail-to-rail performance of the AD820 can be used to pro-

vide low dropout performance for low power reference circuits

powered with a single low voltage supply. Figure 45 shows a

4.5 volt reference using the AD820 and the AD680, a low power

2.5 volt bandgap reference. R2 and R3 set up the required gain

of 1.8 to develop the 4.5 volt output. R1 and C2 form a low-

pass RC filter to reduce the noise contribution of the AD680.

+5V

2

3 U1 6

AD680

C1

4

0.1␮F

U2 6

AD820

7

4

+2.5V ؎10mV

R1

100k⍀

32

C2

0.1␮F FILM

R2

80k⍀

(20k⍀)

+2.5V

OUTPUT

+4.5V

OUTPUT

R3

100k⍀

(25k⍀)

C3

10␮F/25V

REF

COMMON

AD820

Low Power Three-Pole Sallen Key Low-Pass Filter

The AD820’s high input impedance makes it a good selection

for active filters. High value resistors can be used to construct

low frequency filters with capacitors much less than 1 µF. The

AD820’s picoamp level input currents contribute minimal dc

errors.

Figure 46 shows an example, a 10 Hz three-pole Sallen Key

Filter. The high value used for R1 minimizes interaction with

signal source resistance. Pole placement in this version of the

filter minimizes the Q associated with the two-pole section of

the filter. This eliminates any peaking of the noise contribution

of resistors R1, R2, and R3, thus minimizing the inherent out-

put voltage noise of the filter.

C2

0.022␮F

R1

243k⍀

R2

R3

243k⍀ 243k⍀

+VS 0.01␮F

37

VIN

C1

0.022␮F

C3

0.022␮F AD820

6

2

4 0.01␮F

–VS

0

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

0.1

1

10

100

FREQUENCY – Hz

VOUT

1k

Figure 46. 10 Hz Sallen Key Low-Pass Filter

Figure 45. Single Supply 4.5 Volt Low Dropout Reference

With a 1 mA load, this reference maintains the 4.5 volt output

with a supply voltage down to 4.7 volts. The amplitude of the

recovery transient for a 1 mA to 10 mA step change in load

current is under 20 mV, and settles out in a few microseconds.

Output voltage noise is less than 10 µV rms in a 25 kHz noise

bandwidth.

REV. B

–15–

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