12 Biomedical Engineering Fundamentals
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Fig. 12.19 Schematic block diagram of signal acquisition [11]
12.3.3 Signal Acquisition
Signal acquisition is a process in which we study how the physical signals collected
from the sensors get into the computers or digitized for the processing of signal
in computers and machines. The main blocks of signal acquisition process contain
signal conditioning which is mainly possible with a sample and hold circuit and
ADC by which a physical analog signal can be converted into a digital signal.
The block diagram of signal acquisition process along with sensor and computer
interface units is shown in Fig. 12.19. In this Fig. 12.19, sensor senses the physical
signal and then signal conditioning is applied with the help of sample and hold
circuit, and in order to get this signal in digital domain, an ADC is used. Thus,
the converted signal has a number of bits which represent the analog signal at a
particular instant of time and which can be stored in a computer with this interfacing
mechanism [11].
The typical signal acquisition process has some additional processing units
because the sensors have multiple channels. Therefore, a multiplexing unit with
sample and hold circuit which quickly scans all the channels and provides data to
sample and hold circuit in the short interval of time is required. On the other hand,
each ADC has a certain dynamic range of working. The violation of dynamic range
of ADC leads to approximation errors during analog to digital conversion process.
Thus, it is necessary to amplify the signal to increase the resolution of the ADC.
The isolation is also a part of signal acquisition process because the electric and
magnetic fields may affect the signal properties. Therefore, a good signal acquisition
process should be properly isolated in order to get less interference of external
factors. In addition to these abovementioned units, an anti-aliasing filter just after
the multiplexer unit is also required because the outputs from the multiplexer are
very closely placed in time and the sample and hold circuit with ADC will also take
some time to complete the analog to digital conversation process [11].
12.3.4 Time- and Frequency-Domain Representations
The digital signals stored in computer have significant information which enable us
to extract the desired information present in the signal. These signals physically exist
in time domain and we can analyze the behavior for most of the signals by visual
inspection. However, the frequency-domain characterization is equally important for
565
Fig. 12.19 Schematic block diagram of signal acquisition [11]
12.3.3 Signal Acquisition
Signal acquisition is a process in which we study how the physical signals collected
from the sensors get into the computers or digitized for the processing of signal
in computers and machines. The main blocks of signal acquisition process contain
signal conditioning which is mainly possible with a sample and hold circuit and
ADC by which a physical analog signal can be converted into a digital signal.
The block diagram of signal acquisition process along with sensor and computer
interface units is shown in Fig. 12.19. In this Fig. 12.19, sensor senses the physical
signal and then signal conditioning is applied with the help of sample and hold
circuit, and in order to get this signal in digital domain, an ADC is used. Thus,
the converted signal has a number of bits which represent the analog signal at a
particular instant of time and which can be stored in a computer with this interfacing
mechanism [11].
The typical signal acquisition process has some additional processing units
because the sensors have multiple channels. Therefore, a multiplexing unit with
sample and hold circuit which quickly scans all the channels and provides data to
sample and hold circuit in the short interval of time is required. On the other hand,
each ADC has a certain dynamic range of working. The violation of dynamic range
of ADC leads to approximation errors during analog to digital conversion process.
Thus, it is necessary to amplify the signal to increase the resolution of the ADC.
The isolation is also a part of signal acquisition process because the electric and
magnetic fields may affect the signal properties. Therefore, a good signal acquisition
process should be properly isolated in order to get less interference of external
factors. In addition to these abovementioned units, an anti-aliasing filter just after
the multiplexer unit is also required because the outputs from the multiplexer are
very closely placed in time and the sample and hold circuit with ADC will also take
some time to complete the analog to digital conversation process [11].
12.3.4 Time- and Frequency-Domain Representations
The digital signals stored in computer have significant information which enable us
to extract the desired information present in the signal. These signals physically exist
in time domain and we can analyze the behavior for most of the signals by visual
inspection. However, the frequency-domain characterization is equally important for