link to page 19 link to page 19 link to page 19 Data SheetAD8605/AD8606/AD8608I-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. F10pF The maximum achievable signal bandwidth is RF10MΩ ft f = MAX R π 2 FCF PHOTODIODEVOS where ft is the unity gain frequency of the amplifier. CRDAD8605AUDIO AND PDA APPLICATIONSDID50pFVOUT 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. 5VR1C120kΩ81µFC3R4R231/2100µF20ΩV120kΩAD86061500mVR3HEADPHONES21kΩ45VC2R781µF20kΩC4R65R81/2100µF20ΩV220kΩAD86067500mVR561kΩ4 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