Ultra-wideband radio: Unconventional circuit solutions for unconventional communication

The governing body in the United States. the Federal Communications Commission (FCC). has issued ultra-wideband regulations. under Part15 of the Commission's rules on April 22, 2002. Therefore, ultra-wideband transmissions (intentional emissions) under certain frequency and power limitations have been permitted. The US has openly endorsed UWB based consumer products. Ultra-wideband offers significant contributions and advantages but simultaneously a number of challenges also need to be addressed. One of file key challenges is the co-design of an impulse generator and miniaturized antennas for ultra-wideband impulse radio. This has been designed and fabricated in 0.18 mu m CMOS technology. Measurements show the correct operation of the circuit for supply voltages of 1.8V and a power consumption of 45mW. The Output Pulse approximates a Gaussian monocycle having a pulse duration of about 375ps. Proper modulation of the pulse in time is confirilied [1], In addition. to meet the stringent FCC stipulated frequency spectrum, an orthonormal [2] ladder filter with a Daubechies' impulse response is employed. The filter is implemented using novel 2-stage gm-C cells employing negative feedback. Simulation results in CMOS 0.13 mu m technology show that this pulse generator requires a total current of 30mA at a 1.2V power supply. The frequency coverage of the simulated waveform is about 85% of the FCC mask. In receivers, narrowband interference has been acknowledged as a serious impairment for UWB performance. Only limited research has been addressed to evaluate the effects oil transmitted reference (TR) schemes. By employing "frequency wrapping". a new architecture, the Quadrature Downconversion Autocorrelation Receiver (QDAR) has been developed [3]. It does not suffer from timing and template matching problems, and it also circumvents processing at high frequencies. thereby reducing file on-chip circuit complexity and power consumption. Moreover. it not only offers narrowband interference rejection but also relaxes the timing accuracy of the delay circuitry in file auto-correlation function. For the QDAR. a quantized analog delay [4] and a filter based delay line [5] have been designed. For a time delay of 0.55ns, simulation results in CMOS 0.13 mu m technology show that the quantized analog delay requires a total current of 36.7mA at a 1.6V power supply. For the filter based delay, a total current of 30mA at a 1.2V power supply is required to achieve a time delay of 0.72ns. Finally, this paper also addresses double-loop negative feedback amplifier techniques to realize true wideband LNA's [6]. Index Terms-broadband, delay lines, quadrature downconversion, FCC, impulse radio, integrated circuits, low-noise amplifiers, negative feedback, transceivers, transmitted reference, ultra-wideband.