
Principles of Analog Electronics
364
energy in a form of a current at high impedance. A
photomultiplier or a capacitive sensor or a solar cell
are also current-producing devices, but their current
can have a very low value. It is possible to convert
the input current to an analog output voltage simply
by using a load resistor, but the voltage available is
often only a few tens of millivolts. A transresistance
amplier can solve the problem.
Let’s go deeper. We want to reveal a weak light
radiation. A photodiode PD is useful to convert light
into a current converted into a voltage by means of
a resistor R. This voltage feeds a load impedance Z