| As an important part of the brain-machine interface,implantable biomedical electronic devices are responsible for the acquisition,processing,and transmission of bioelectric signals.Wireless Transmitter is a important part in biomedical electronic systems.the traditional narrow-band communication method transmit signals through carrier by up-conversion is not conducive to realize low-voltage and low-power supply.Ultra-wideband(UWB)wireless communication is more suitable to transmit data in biomedical electronic devices due to its low power consumtion and simpler structure.In order to reduce system power consumption,rencently studies have shown that under power constraints,when the supply voltage is reduced to 1-V,the amplitude of output pulse will be significantly reduced,only tens of millivolts,which is too diffcuclt for receiver to capture the wireless signals.At the same time,with the speed of data processing,we should consider more on the transmission rate.In order to optimize the maximum transmission rate of the transmitter and improve the amplitude of output pulse amplitude under low voltage supply,in this paper,based on the existing research,a new multi-pulse combining method of ultra-wide band communication is proposed,which has the technical advantages that a controllable delay unit and the enhancement pulse amplitude.Its design parameter and innovations includes:1.Output enhancement technology: The proposed pulse generator based on the multiple-pulse combination technology.In order to improve the amplitude of output pulse at low power supply,a pulse amplitude enhancement circuit has been designed,which raises the amplitude of 2nd and 3rd pulse due to the charge between the two capacitor plates cannot be changed suddenly.In the same time of charg and discharg,the raised pulse decreases the equivalent resistance of the MOS transistor and increases the equivalent current of the MOS transistor as well,So that the amplitude of generated UWB pulse can me improved.And it will facilitates the capture of wireless signals by the receiver.2.Optimization of transmission rate based on different coding: Barker code has better coding gain and can effectively reduce the bit error rate.The proposed UWB transmitter is designed with 11-bit and 7-bit Barker encoder,the transmitted as the ctrl signal to select the generated Barker sequence to complete the coding.The maximum transmission rate RB is 1/11 and 1/7 of the frequency of main clock,but the introduction of multi-stage D flip-flops in the Barker coder,a large amount of layout area is occupied.In order to increase the transmission rate and reduce the chip area,an Manchester encoder is designed,it increases RB to 1/2 of the frequency of main clock.And the chip area is significantly reduced.3.Pulse width tunning technology: The generation of narrow pulses is the key of ultra-wideband pulses.In order to against the variation of temperature,process,and environment,and generate a more stable UWB pulses,a controllable delay circuit is proposed in this paper,through the turn-on and turn-off of MOS transistors.Each branch is selectively incorporated into the circuit,which will chang the equivalent current by change the equivalent resistance,thereby changing the delay time,realizaing the pulse width regulation.The proposed UWB transmitter in this paper is designed using a 0.18?m CMOS process.The the smallest chip area(89.7?m*74.8?m)Manchester-encoded transmitter which has the highest transmission rate is streamed.The test result shows that under maximum transmission rate 50 MHz,the system power consumtion is only 559?W,the amplitude of output pulse is increased from 43.15 mV which is generated by traditional system to 105.32 mV,the pulse width achieves an eight-level,range from 7.2ns to 9.4ns controllable.The power spectral density of generated UWB pulse is sub-GHz,causing little damage to the human body,and it could meet the FCC(Federal Communications Commission)requirements for UWB communications. |
PDF Full Text Request