Datasheet AD8605, AD8606, AD8608 (Analog Devices) - 19

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Data Sheet AD8605/AD8606/AD8608 I-V CONVERSION APPLICATIONS PHOTODIODE PREAMPLIFIER APPLICATIONS
At room temperature, the AD8605 has an input bias current of The low offset voltage and input current of the AD8605 make 0.2 pA and an offset voltage of 100 µV. Typical values of RD are it an excellent choice for photodiode applications. In addition, in the range of 1 GΩ. the low voltage and current noise make the amplifier ideal for For the circuit shown in Figure 52, the output error voltage is application circuits with high sensitivity. approximately 100 µV at room temperature, increasing to about
C
1 mV at 85°C.
F 10pF
The maximum achievable signal bandwidth is
RF 10MΩ
ft f = MAX R π 2 FCF
PHOTODIODE VOS
where ft is the unity gain frequency of the amplifier.
C R D AD8605 AUDIO AND PDA APPLICATIONS D ID 50pF VOUT
The low distortion and wide dynamic range of the AD860x 051 make it a great choice for audio and PDA applications, 02731- including microphone amplification and line output buffering. Figure 52. Equivalent Circuit for Photodiode Preamp Figure 53 shows a typical application circuit for headphone/ The input bias current of the amplifier contributes an error line-out amplification. term that is proportional to the value of RF. R1 and R2 are used to bias the input voltage at half the supply, The offset voltage causes a dark current induced by the shunt which maximizes the signal bandwidth range. C1 and C2 are resistance of the Diode RD. These error terms are combined at used to ac couple the input signal. C1, R1, and R2 form a high- the output of the amplifier. The error voltage is written as pass filter whose corner frequency is 1/[2π(R1||R2)C1].  R  The high output current of the AD8606 al ows it to drive heavy F E = 1+ + O OS V R   F I B  R resistive loads. D  Typically, R The circuit in Figure 53 is tested to drive a 16 Ω headphone. The F is smaller than RD, thus RF/RD can be ignored. THD + N is maintained at approximately −60 dB throughout the audio range.
5V R1 C1 20kΩ 8 1µF C3 R4 R2 3 1/2 100µF 20Ω V1 20kΩ AD8606 1 500mV R3 HEADPHONES 2 1kΩ 4 5V C2 R7 8 1µF 20kΩ C4 R6 5 R8 1/2 100µF 20Ω V2 20kΩ AD8606 7 500mV R5 6 1kΩ 4
052 02731- Figure 53. Single-Supply Headphone/Speaker Amplifier Rev. N | Page 19 of 24 Document Outline Features Applications General Description Pin Configurations Revision History 5 V Electrical Specifications 2.7 V Electrical Specifications Absolute Maximum Ratings ESD Caution Typical Performance Characteristics Applications Information Output Phase Reversal Maximum Power Dissipation Input Overvoltage Protection THD + Noise Total Noise Including Source Resistors Channel Separation Capacitive Load Drive Light Sensitivity WLCSP Assembly Considerations I-V Conversion Applications Photodiode Preamplifier Applications Audio and PDA Applications Instrumentation Amplifiers DAC Conversion Outline Dimensions Ordering Guide