| 摘要 |
1. Switched capacities active filter the transfer function of z, T(z), is of the form T(z) = z**-k . P(z**-1 )/Q(z**-1 ), wherein P(z**-1 ) and Q(z**-1 ) are two polynominals of z**-1 of the degrees m and n and of the form : P(z**-1 ) = p0 + p1 z**-1 + ... + pm z**-m Q(z**-1 ) = q0 + q1 z**-1 + ... + qn z**-n with p0 Not= 0, q0 Not= 0 and k >= 0, characterized in that m is strictly greater than n, and in that the structure of this filter is obtained in the following manner : equality is established between the transfer function T(z) and the ratio of the determinants of two square matrices A and B of p lines and p columns, wherein p represents the greatest value of m and of n, each of the terms of these matrices being a polynominal of z**-1 of the first order and of the form aij . z**-1 + bij , and the two matrices differing only in the terms of their last column : T(z) = P(z**-1 )/Q(z**-1 ) = Det A/Det B from this equality the coefficients aij and bij are determined so that the polynominals aij . z**-1 + bij can be obtained by the parallel connection of conventional switched capacities devices and of capacities ; the p equations resulting from the following relation are provided : Matrix B see diagramm : EP0058113,P11,F1 wherein Ve represents the input voltage of the filter, wherein V1 , V2 ... Vp represent the output voltages of the p differential amplifiers the filter comprises and wherein the polynominals associated with Ve originate from the last column of the matrix A ; the electrical diagram of the filter is established from these equations, each equation corresponding to a differential amplifier (1, 2, 3, 4) having its positive input connected to ground and supplying an output voltage Vi the coefficient associated with -Ve within this equation corresponding to conventional switched capacity devices connected in parallel to capacities (10, 20, 30, 40) embodying these coefficients and which are inserted between the negative input of the amplifier and the input voltage Ve , the coefficients associated with the other voltages V1 ... Vp , except for Ve , corresponding to conventional switched capacities devices connected in parallel to capacities (12, 13, 14, 22, 23 ...) embodying these coefficients and which are placed between the negative input of the amplifier supplying Vi and the output of the amplifiers supplying the voltages V1 ... Vp , except for Vi , and the coefficient associated with the voltage Vi corresponding to at least one capacity (C) placed between the output of the amplifier supplying the output voltage Vi and the negative input of this amplifier, conventional switched capacities devices and further capacities (11, 22, 33, 44) being eventually provided in parallel to this capacity, the output of the filter being derived from the output of the pith amplifier and the eventual delay z**-k being obtained separately. |
