TABLE OF CONTENTS Many popular sensors have output impedances greater than several M ?, and the associated signal conditioning circuitry must be carefully designed to meet the challenges of low bias current, low noise, and high gain. A large portion of this section is devoted to the analysis of a photodiode preamplifier. This application points out many of the problems associated with high impedance sensor signal conditioning circuits and offers practical solutions which can be applied to practically all such sensors. Other examples of high impedance sensors discussed are piezoelectric sensors, charge output sensors, and charge coupled devices (CCDs).
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Photodiodes generate a small current which is proportional to the level of illumination. They have many applications ranging from precision light meters to high-speed fiber optic receivers.
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The equivalent circuit for a photodiode is shown in Figure 4.4.3. One of the standard methods for specifying the sensitivity of a photodiode is to state its short circuit photocurrent (I SC) at a given light level from...
