Research On Implementation Of Wavelet Transform Using Switched Current Technology

Wavelet transform (WT), being called mathematical microscope, has been a new style mathematic analysis method and generated a tremendous interest in both theoretical and applied areas, especially over the past few years. The Wavelet transform is a linear operator that decomposes a signal into components that appear at different scales and gives good estimation of time and frequency localization. Wavelet transform is a powerful tool for analyzing non-stationary and fast transient signals for its excellent characteristic so that it has found widespread use in various signal processing applications, such as image processing, speech analysis, pattern recognition, signal detection, feature abstraction, fault diagnosis and orientation, data compact, etc.There exists two ways for the realization of wavelet transform: the Discrete Wavelet Transform (DWT) and the Continuous Wavelet Transform (CWT). However, a principal obstacle to the wider utilization of wavelet transform is the heavy computational cost. Consequently, analog implementations of WT have been an attractive option to achieve real-time performance. One of the main prospective developing directions of VLSI is the implementation of low-voltage, low-power analog circuits, for which switched current (SI) technique is an attractive solution. The switched current technique, based on current mode, is a relatively new analog sampled-data signal processing technique that aims to replace switched-capacitors (SC). In contrast to the SC technique, which requires a nonstandard digital CMOS process to realize floating linear capacitors, SI technique can perform accurate signal processing functions in a standard digital CMOS process without the direct use of any capacitor. Moreover, the SI technique does not utilize CMOS op-amps but rather performs its entire analog signal processing with much simpler current mirrors. In a word, the advantages of the SI are its simplicity of implementation, potential for high speed, low-voltage operation and compatibility with digital CMOS processes, which is an attractive feature due to the tendency for the integration of large analog/digital systems in a single chip.In this paper, typical implementations of WT are generalized. The systemic realizations of WT, based on SI circuits, are firstly proposed. The research is carried out in the following aspects: 1. The solution methods of WT based on frequency-domain, using SI circuits, are studied systematically. Complex demodulation scheme is provided for realizing WT based on SI circuits. The SI circuits, including SI oscillator, SI multiplier and SI Gaussian low pass filter, and the system are both given and verified by simulated results.2. Method for realizing time-domain WT using SI technology is presented in this paper, which is shown a new way for fast implementation of WT based on amplitude modulation techniques for generating wavelet chain. SI low pass filter is synthesized with SI integrators based on bilinear transform. Thus, It provides a solution to manufacture integrated chip of time-domain WT. The SI low pass filter is simulated using ASIZ and shown to be able to meet the needs of time-domain WT. Then, the good performance of time-domain WT is verified by system simulated results.3. Padéapproximation is proposed for the implementation of wavelet filter. Wavelet filter banks, whose impulse responses are the first derivative of Gaussian and its dilations, play a key role in analog VLSI implementation of wavelet transform. The transfer functions of the filters can be given by Padéapproximation, which is able to decompose the transfer function into rational form so as to be conveniently implemented by SI circuits. So, it is easy for achieve wavelet filters according to the basic theory of filter.4. Method for realizing Morlet wavelet transform using SI circuits is presented in frequency-domain and time-domain, respectively. In frequency-domain, SI integrators are used to synthesize Gaussian band pass filter by using leapfrog configuration to simulate passive ladder filter. Then, Morlet wavelet filter and reconstruction filter are synthesized. Only one couple of wavelet filter and reconstruction filter are needed to be designed to realize dyadic wavelet transform according to the perfect character of SI. The provided method is simple to be implemented and propitious to be used to manufacture integrated chip. Method for the design and implementation of Morlet wavelet transform in time-domain, using switched current circuits, is proposed. The SI Gaussian function generator, playing a key role in the implementation of Morlet wavelet transform, is firstly realized using SI circuits.5. Based on the implementation of Gaussian unit using SI circuits, new WT systems with share units array have been presented by analyzing three kinds of expressions of wavelet functions, including Marr wavelet, Morlet wavelet and DOG wavelet, which have similar construction according to the expression of WT both in time-domain and frequency-domain. It is very useful for the presented system to change aims of wavelet transform chips from specific aims to generic aims. Then, the orthogonal wavelet transform is discussed, which is implemented by SI circuits using Laguerre structure.