When the transmitter is configured to operate with gating control at 25 percent duty cycle during transmission of baseband signals from a transmitter to a target, the impulse UWB transmitter can achieve up to four times better performance.
This gated signal can then achieve the same average transmit power as a continuous signal while occupying only a fraction of the channel time available for transmissions in the UWB system. The core component of the pulse generator is the edge generator, as shown in Figure 5.
The edge generator generates the basic element which is the Gaussian pulse. The pulse width and pulse amplitude are controlled through the delay elements. The pulse generation logic is that when one XOR input is slower than the other XOR input, the time difference between these input produces a positive normally distributed voltage pulse usually represented by Gaussian distribution , and when the inverted NAND input is slower than the other NAND input, the time difference of these two input produces a negative normally distributed voltage pulse.
The polarity of the edge generator output is control by Vctrl. The Vctrl select either the positive pulse or the negative pulse to pass to the output through the AND and OR logic gates. Edge generator circuit with edge tuning capability. Block diagram of the pulse generator. The Gaussian derivative pulse generator, as shown in Fig. Each edge generator produces a single pulse with different amplitude and the same pulse width T delay. The delay in each edge generator is adjusted based on the shape factor of the tenth derivative of the Gaussian pulse.
The control signal is inverted at the 2nd, 4th, 6th, and 8th edge generators to produce pulses with negative polarity at these locations. The final output of the tenth derivative Gaussian pulse is constructed based on each single edge generator output. The design is a transmitter prototype.
It not only can generate tenth-order Gaussian derivative, but any pulse combinations, either Gaussian derivatives or rectangular or Gaussian modulated sine pulses by controlling the delay elements in each edge generator and the number of edge generators used based on different orders of derivative of Gaussian pulse, the bandwidth, and the center frequency.
The base-band signal was generated at Mbps to leave enough headroom for pulse generation. The positive and negative tenth derivative Gaussian pulses were generated, as shown in Figure 7. The pulse width was adjusted to 0. The transmitter output peak-to-peak amplitude is mV, and the amplitude ranges from 35mV to mV. A Monte Carlo simulation was performed to validate the robustness of the transmitter circuit against process voltage and temperature variations and mismatches.
The Monte Carlos simulation results of the tenth-order Gaussian derivative pulses are shown in Figure 8. The simulated power spectral density plot of the transmitter output with simulated white noise added is shown in Figure 9.
The layout of the proposed transmitter is shown in Figure The transmitter core occupies a chip area of um by um. Simulating on a 1V voltage supply, the transmitter draws average 9.
The pulse width is 0. The transmitter has output pulse energy of 3. The proposed impulse-based UWB technique enormously reduces the circuitry complexity and power consumption. Figure 11 shows the block diagram of the transmitter which consists of a modulator, a pulse generator, and a variable gain amplifier VGA driver, and a ring oscillator.
The VGA and driver are used to amplify and adjust the output pulse, as well as for impedance matching. The incoming data V d a t a is modulated with clock train generated by the ring oscillator, yielding a sequence of clock pulse, which then enters the pulse generator to produce a pulse train. This pulse train is passed onto a driver amplifier and then to an.
Simulated tenth order Gaussian derivative pulses. Monte Carlo simulation of the transmitter. Simulated power spectral density of the pulse. Layout of the proposed digital transmitter. UWB antenna. The output pulse amplitude is adjustable through the variable gain amplifier in the driver. The transmitter is fabricated using CMOS 90nm process, and the whole design consumes less than 0.
The clock signal Clk, generated by a ring oscillator, has a period of 1ns and a pulse width of ps. The number of pulses in one bit of data is determined by both the bit length and the clock frequency.
For radar sensing purpose, it is the best interest of the energy-collecting receiver to include more pulses in a single pulse train sent to the target for a good SNR and easy detection. In communication cases, the number of pulses representing one bit is set less for higher data transmission rate. The clock rate is higher than the data rate to ensure reliable modulation and demodulation. Figure 12 b illustrates the pulse generator and modulator in the transistor level. Pulse generator and modulator circuit in transistor level.
Timing waveforms of the transmitter. The signal flow at each block of the proposed transmitter is illustrated in Figure The transmitter clock signal is represented by A. B is the input digital sequence. The modulated clock train C passes through an inverter chain to sharpen the rising and falling edge of the each clock signal. The modulated clock train is then split into two signal paths and fed into a NOR gate. Signals in one path is delayed and inverted, as shown by D.
The NOR gate only outputs high when both inputs are low, and the time for both inputs be low is the delay time set by the inverter chain in the delay path. The signal E represents the output pulses. The output pulse width is determined by this delay time. The output pulse width can be adjusted by changing the delay of the inverters, which in turn, by varying the load capacitance of the inverters.
Figure 14 shows the simulated pulses with various pulse widths when changing the load capacitance of the inverters C L. On the y-axis is the time of flight ToF calculated from the following parameters: i number of captured samples, ii sampling rate of the ADC, iii time stretch ratio of the sampler.
From the ToF it is possible to calculate the penetrating depth of the RF signal according to the surrounding material, since the propagation velocity of an RF signal is dependent on the dielectric constant of the material. The pulse generator and sampler designs were improved and implemented using commercially available low cost electronic components.
An existing design of a pulse-based radar using SRD was improved by removing the negative power supply, resulting in a reduced number of electronic components. To receive ultra wide band pulses, a signal stretcher was improved by using the improved pulse generator as a strobe pulse generator, which made the design much simpler, and enabled us to acquire a received signal using a much lower sample rate.
A micro controller with a Linux operating system called Red Pitaya was used for all signal manipulations, acquisition, signal processing, and communication with peripheral devices. Conceptualization, M. All authors have read and agreed to the published version of the manuscript. National Center for Biotechnology Information , U. Journal List Sensors Basel v. Sensors Basel. Published online May Author information Article notes Copyright and License information Disclaimer.
Received Mar 24; Accepted May Abstract This paper proposes an improved design of a pulse-based radar. Keywords: ultra-wide-band, pulse radar, ground penetrating radar, sampling mixer, pulse generator. Introduction Ultra-wide-band UWB radars produce very short radio-frequency RF pulses in the range of a sub-nanosecond order and are used for sensing and imaging applications.
Open in a separate window. Figure 1. Development of the Sub-Nanosecond Pulse Generator This section presents a pulse-based generator using step recovery diodes SRD , due to its simple implementation and ability to produce pulses in the range of hundreds of picoseconds with an amplitude of mV.
Figure 2. Figure 3. Figure 4. Development of the Sampling Mixer The design of a sub-nanoseconds pulse generator is much simpler compared to design of the UWB receiver. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure Picture of the proposed radar attached on the Red Pitaya micro-controller. Author Contributions Conceptualization, M.
Conflicts of Interest The authors declare no conflict of interest. References 1. IEEE Trans. Theory Tech. Oloumi D. Feghhi R. Nicolaescu I. Sugak V. Charvat G. Small and Short-Range Radar Systems. CRC Press Inc. Liu L. IEEE Sens. Beev N. Note: An avalanche transistor-based nanosecond pulse generator with 25 MHz repetition rate. Huang Z. Matiss A. Johnson J. Han J. On the development of a compact sub-nanosecond tunable monocycle pulse transmitter for UWB applications.
Jeongwoo H. Coupled-slotline-hybrid sampling mixer integrated with step-recovery-diode pulse generator for UWB applications. Zou L. IEEE Microw. Texas Instruments, Inc. Venkatachalam A. IEEE J. Earth Obs. Remote Sens. The spectrum of a very narrow-width pulse has a very large frequency spectrum approaching that of white noise as the pulse becomes narrower and narrower.
These very short pulses need a wider receiver bandwidth as conventional radar systems. The amount of spectrum occupied by a signal transmitted by a UWB-radar i. The data from the conducted actuator experiments were used for testing the presented algorithm. Figure 22 shows the SD values for the proposed method using the data from experiment 4 and the corresponding range and frequency estimation results are given in Figs 23 and 24 , respectively.
The frequency estimate from Fig. The frequency estimate using the CSD method from Fig. The FFT method provides the worst performance as the frequency estimate from Fig. Compared with the actual frequency of 0. The frequency estimates using the outdoor data from experiment iii is shown in Fig. The frequency estimates and corresponding deviations are given in Table 4 for three trials of the experiment. All these results indicate that the presented algorithm has the smallest deviation and significantly outperforms the other algorithms.
Vital sign detection was considered in this paper for applications such as after a natural disaster. The respiration and heartbeat frequencies were estimated using an impulse UWB radar. The discrete short-time Fourier transform DSFT of the calculated standard deviation SD values was used to estimate the range information of the volunteer. Experimental data obtained using a UWB radar were used to evaluate the performance of several techniques.
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