Biomedical Engineering Reference
In-Depth Information
-41.3 dBm / MHz
4 GHz
Fig. 5.18
Transmit spectrum at 40 MHz PRF
sections during an intermittent data transmission situation to reduce the power
consumption of the sensor node. The micro-controller also acts as the mediator for
analog and digital data inputs. It performs the analog to digital conversion using a
ten-bit ADC, determines the transmission format and the modulation scheme, and
sets the data rate.
The ADC of the sensor node can operate at 20 kHz sampling rate, which is
sufficient for physiological signals, such as ECG. The ADC can operate during the
sleep mode without consuming much power, hence sensor data acquisition can be
performed in between the data transmission periods. The micro-controller runs an
internal clock that can operate at a maximum frequency of 60 MHz. IR-UWB
pulse rate is independent of the data rate and is arranged by the pulse generator.
The UWB pulses generated by the pulse generator are multiplied with the binary
data bits created by the micro-controller using an AND gate. The micro-controller
used in this design can generate data up to a data rate of 5 Mbps using its digital
output pins. Hence, the maximum data rate that can be generated by a sensor node
is limited to 5 Mbps. It should be noted that higher data rates could be achieved by
choosing a micro-controller with higher performance at the cost of slightly higher
power consumption. The implementation of the MAC protocol in the micro-
controller is discussed further in
Chap. 6
.
