Dual-Channel Colorimeter with Programmable Gain Transimpedance Amplifiers and Synchronous Detectors (CN0312.pdf)
* OpAmp AD8615
Switch ADG633
Switch ADG733
* OpAmp AD8271
OpAmp AD8618


5 kHz LED Clock

Note that the feedback capacitor, CFx, is required for stability to compensate for the pole introduced by the total input capacitance (diode capacitance plus op amp input capacitance) and the feedback resistor, RFx. For details of this analysis, see Section 5 of Practical Design Techniques for Sensor Signal Conditioning.

The output voltage of the photodiode amplifier swings between 2.5 V and 5.0 V.
For the 33 kOhm range, this 2.5 V output span corresponds to a full-scale photodiode current of 75.8 µA.
For the 1 MOhm range, it corresponds to a full-scale photodiode current of 2.5 µA.

The next stage is a simple buffered ac-coupled filter. The cutoff frequency of the filter is set at 7.2 Hz.

2016

Application Note Analog Devices
CN0312 Dual-Channel Colorimeter with Programmable Gain Transimpedance Amplifiers and Synchronous Detectors
Video:
Video

2020 Nachfolgeprodukt

Analog Devices CN0363 Dual-Channel Colorimeter 24.3.2020
Video

TIA Amplifier R1 = 1 MOhm, VDD = 5V, Vref = 2.5 V Uout(IPh) = - IPh · R1 + Vref \( I_{Phmax} = - \frac{U_{out} - V_{ref}}{R_1} = - \frac{V_{DD} - V_{ref}}{R_1} = - \frac{2.5}{10M \Omega} = 2.5 \mu A \)
Hochpass C = 0.22 µF, R = 10 kΩ \( \frac{\underline{U_a}}{\underline{U_e}} = \frac{R}{\frac{1}{j \omega C} + R } = \frac{j \omega C R}{1 + j \omega C R } \) \( f = \frac{1}{2 \pi C R } = 72.3 Hz \)
AD8271 \( V_x = \frac{V_2 - V_{ref}}{2} + V_{ref} \) \( V_x = \frac{V_2}{2} + \frac{V_{ref}}{2} \) \( \frac{V_1 - V_x }{R} = I_1 = \frac{V_x - V_{out} }{R} \) Vout = 2 Vx - V1 Vout = V2 + Vref - V1 Schalterstellung 1 (hoher Pegel Vin): Vout = Vin + Vref - Vref = Vin Schalterstellung 2 (niedriger Pegel Vin): Vout = Vvref + Vvref - Vin = 2 Vvref - Vin
Tiefpass C = 1 µF, R = 10 kΩ \( \frac{\underline{U_a}}{\underline{U_e}} = \frac{\frac{1}{j \omega C}}{R + \frac{1}{j \omega C}} = \frac{1}{1 + j \omega C R } \) \( f = \frac{1}{2 \pi C R } = 15.9 Hz \)

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SYMATTR Value AD8615
SYMATTR Prefix X
SYMATTR SpiceModel AD8615.cir
SYMATTR Value2 AD8615
SYMATTR Description Precision Operational Amplifier

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