AD8605(RevD) 查看數據表（PDF） - Analog Devices

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AD8605
(Rev.:RevD)

Precision Low Noise CMOS Rail-to-Rail Input/Output Operational Amplifiers

Analog Devices 

AD8605/AD8606/AD8608

I-V CONVERSION APPLICATIONS

PHOTODIODE PREAMPLIFIER APPLICATIONS

The low offset voltage and input current of the AD8605 make it

an excellent choice for photodiode applications. In addition, the

low voltage and current noise make the amplifier ideal for

application circuits with high sensitivity.

CF

10pF

RF

10MΩ

PHOTODIODE

RD

ID

CD

50pF

+VOS–

AD8605

VOUT

Figure 51. Equivalent Circuit for Photodiode Preamp

The input bias current of the amplifier contributes an error

term that is proportional to the value of RF.

The offset voltage causes a dark current induced by the shunt

resistance of the diode RD. These error terms are combined at

the output of the amplifier. The error voltage is written as

EO

= VOS

⎜⎜⎝⎛1 +

RF

RD

⎟⎟⎠⎞

+

RF IB

Typically, RF is smaller than RD, thus RF/RD can be ignored.

At room temperature, the AD8605 has an input bias current of

0.2 pA and an offset voltage of 100 µV. Typical values of RD are

in the range of 1 GΩ.

For the circuit shown in Figure 9, the output error voltage is

approximately 100 µV at room temperature, increasing to about

1 mV at 85°C.

Where ft is the unity gain frequency of the amplifier, the

maximum achievable signal bandwidth is

fMAX =

ft

2πRFCT

AUDIO AND PDA APPLICATIONS

The AD8605’s low distortion and wide dynamic range make it a

great choice for audio and PDA applications, including

microphone amplification and line output buffering.

Figure 52 shows a typical application circuit for headphone/line

out amplification.

R1 and R2 are used to bias the input voltage at half the supply.

This maximizes the signal bandwidth range. C1 and C2 are used

to ac couple the input signal. C1 and R2 form a high-pass filter

whose corner frequency is 1/2πR1C1.

The high output current of the AD8605 allows it to drive heavy

resistive loads.

The circuit of Figure 52 was tested to drive a 16 W headphone.

The THD + N is maintained at approximately −60 dB

throughout the audio range.

5V

R1

C1 10kΩ

1µF

R2

V1

10kΩ

500mV

8

3 1/2

AD8606

2

4

C3

R4

100µF 20Ω

1

R3 HEADPHONES

1kΩ

C2

1µF

V2

500mV

5V

8

5 1/2

AD8606

6

4

C4

R6

100µF 20Ω

7

R5

1kΩ

Figure 52. Single-Supply Headphone/Speaker Amplifier

Rev. D | Page 16 of 20

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