High-order Universal Log-domain Filter Design

Log-domain filter makes use of the active devices'exponential I-V characteristics. The input signal is compressed logarithmically before being processed then expanded exponentially at the output. As a filter of externally linear internally nonlinear, log-domain filter has the advantages of low power consumption, low vantage supply, high operating frequency, wide tune-ability and large dynamic range potentials. Adaptting to the basic requirements of the system and the development trend of IC. Therefore, the study on the log-domain filter design has a very important value.In the thesis, after analyzing the ideal of design low-pass log-domain filter derived from the transfer function, a method of low-voltage low-pass log-domain filter is proposed, and a high-order universal log-domain filter is designed. The work is reported as follows:1) The state-space description of the transfer function. We need to structural features of state-space, and find out the best expression of the state space. When using the state-space to describe input and output equations, derived from the system function, by setting state variables; The state-space descriptions of low-pass and universal filters were optimized.2) Design of translinear cell. The key of log-domain filters design is to design the translinear cell; According to the current characteristics of translinear cell, each item in state-space was combined with the translinear cell, and then achieve log-domain filter. The best translinear cell was obtained by analyzing the connection and circuit characteristics of various translinear cells.3) Low-voltage low-pass log-domain filter. The filter was described by the best translinear cell and state-space. To test the advantage of the proposed method, Various Chebyshev and Butterworth low-pass filters were implemented by using the different state-space and the different translinear cell. Pspice simulation shows that the proposed method is optimal, and the voltage can be reduced to 1.2V.4) High-order universal log-domain filter. Based on the low-voltage low-pass log-domain filter, by analyzing the relative among low-pass, high-pass, band-pass and notch filter, a high-order multi-put universal filter is proposed. Pspice simulations indicate that the proposed circuits are effective.