Design Of Several Circuit Blocks In Uwb System And Audio Sigma-Delta Modulator

Ultra-wideband communication system is a new person area communication system which has a very high bandwidth occupation. One of the solutions for this kind of system is the IR-UWB system, which uses very narrow pulses as the information carrier. This paper provides the design of several circuit blocks used in this IR-UWB system in 0.18um SMIC COMS technology, as follows:1. A new variable Gain amplifier(VGA), designed for a zero-IF receiver in UWB system, is presented. The traditional VGA realizes the variable gain by adjusting the current in the main amplifier's MOSFET and the diode-connected load transistors. However, due to its inherent principle, its linearity is bad at the low-gain mode, and cannot meets the requirement of our system. The new VGA in this paper can provide a ouput 1dB compression output power of 0dBm after the source follower buffer, in all the gian mode bettween 0dB and 45dB, and can meet the requirement of receiver.2. A sub-1-ppm/℃large-supply-range (2.2V-3.5V) CMOS bandgap voltage reference and a new trimming method are presented. The proposed bandgap circuit, implemented in 0.18μm SMIC technology, can provide voltage references: 0-1.2V with a TC of 0.8ppm/℃and 1.2V-1.5V with a TC of below 0.96ppm/℃, in the range from -40℃to 105℃. It also can provide current with good TC, limited to the external resistor used in the voltage-to-current converter. The trimming circuit can provide 16 levels, while needing only one additional pad.3. This paper realizes an integrated very narrow weak pulse detection system by using 0.18um CMOS technology. The chip includes input matching, amplifiers, comparator, delayer, driver and bandgap reference. To improve sensitivity of the detection system, the paper adopts multi-stage cascaded amplifiers as well as active inductors. Test results show that the chip can detect 1ns 10mV pulses, and export digital signals, which can be used in OOK system receiver, receiving more than 40M data-rate video.4. In this paper, a differential power amplifier (PA), designed using Linear-phase filter model, for a BPSK modulated ultrawideband (UWB) system operating in the 3-5GHz frequency range is presented. To achieve sufficient linearity and efficiency, this PA operates in the Class-AB region, delivering an output power of 8.5dBm at an input 1dB compression point of -0.5dBm for a 4 GHz signal. It realizes a flat gain of 9.11±0.39dB and a very low Group delay ripple of +8ps across the whole band of operation.Sigma-Delta ADC's birth is due to the using of the theory of modern autocontrol in the circuit designing region. Its basic theory came to maturity in 1980~1990. With the development of CMOS technology, Sigma-delta ADC has replaced other kinds of ADCs in the high-resolution low rate region. This paper designs an audio Sigma-Delta modulator, adopting a forth-order forward feed construction. Simulation results show that the highest SNR can be achieved when a 9.4kHz sine wave is applied to the modulator is 99dB. The total power consumption is about 1mW.