Biomedical Engineering Reference
In-Depth Information
FIGURE 5-29
Current-to-voltage
converter.
(LTI) system exactly. The outputs of the various integrators therefore correspond to the
state-space model's state variables and become the low-pass, high-pass, and band-pass
filter outputs.
Design of these filters is mostly done using any of a large number of web-based
packages or applets supplied with electronic design automation (EDA) software.
5.4.3 Other Analog Circuits
5.4.3.1 Current-to-Voltage Converter
Many sensor types output a current rather than a voltage and include photomultiplier- and
photodiode-based devices. However, it is inconvenient to process currents using the analog
techniques discussed in this section or to digitize them for further processing. The circuit
shown in Figure 5-29, based on the inverting amplifier, is a simple method to convert a
current to a voltage
V
out
=
I
in
R
(5.23)
The advantage of using this circuit rather than a simple resistor is that the current
flows into a virtual ground, eliminating the effects of the internal resistance of the current
source.
5.4.3.2 Summing Amplifier
The circuit shown in Figure 5-30 operates in a similar manner to the standard inverting
amplifier except that the current at node A comprises the currents from the three inputs
and that fed back from the output. With all resistor values equal, the currents through each
of the three resistors will be proportional to their respective input voltages. Since those
FIGURE 5-30
Summing amplifier.
