Design Description

Transimpedance amplifiers (TIA) are commonly used to amplify the output of current-based sensors like photodiodes. Applications in spacecraft can range from scientific instruments like precision UV spectrometers, to precision optical encoders for motor driver feedback. TIA circuits can be deceptively simple; the proper design of a single-supply photodiode amplifier requires the consideration of many factors including stability and input and output voltage range limitations. Furthermore, the effects of DC error sources such as input bias current and input offset voltage are often ignored and can degrade the accuracy of the circuit.

This application brief examines the proper design process for a rad hard photodiode transimpedance amplifier (TIA) using the QMLV, radiation-hardness-assured (RHA) LMP7704-SP precision op amp as the TIA. The system is assumed to only offer a single 5.0-V supply and the TIA maximum output voltage is determined by the ADC maximum input voltage which is assumed to be 2.5 V.