Photo Diode Amplifier

This small module is a photodiode amplifier. The circuit consists of an OPAMP configured as a transimpedance amplifier for amplifying the light-dependent current of the photodiode. A small bias voltage is derived from the positive supply and applied to the op amp’s non-inverting input. This prevents the output from saturating at the negative supply rail in the absence of input current. For this design, the photodiode operates in photoconductive mode: exposure to light will cause a reverse current through the photodiode. The diode is connected such that this current causes the OPAMP output voltage to increase. The feedback capacitor C5 helps to maintain stability. This capacitor compensates for the photodiode capacitance at the inverting input of the OPAMP. Finally, in the absence of any photodiode current, the amplifier output will attempt to settle at the voltage applied to the non-inverting input. If the non-inverting input is grounded, the output voltage would ideally be 0V. However, the output voltage can never reach 0V because this is also the value of the negative power supply. Therefore, the OPAMP output will “saturate” near its negative power supply. This condition is undesirable and can delay the amplifier’s response to an input signal. To avoid saturation, a resistor divider R1 and R2 from the positive supply is used to bias the amplifier input above ground. The output swing of this amplifier is from 0.1V to 4.9V. The project was built using OPA320 OPAMP which is a new generation of precision, low-voltage CMOS operational amplifiers optimized for very low noise and wide bandwidth while operating on a low quiescent current of only 1.45 mA.

Features

• Supply Voltage 5V DC
• Supply Current 2mA
• Input current 0 – 90μA
• Output: 100mV – 4.9V
• PCB Dimensions 21.11 x 15.24 mm

Schematic

Parts List

Connections

Gerber View

Photos

Video

OPA320 Datasheet

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