A new type circuit of switched‐capacitor transversal filter using transfer function coefficient ratios

Abstract

AbstractThe switched‐capacitor (SC) filter is considered to be a very practical one for integrated circuit (IC) realization due to its ease of high‐accuracy realization because the coefficients of the transfer function can be realized with the capacitance ratio of the capacitors. However, when the coefficients of the transfer function are widely spread, the spread of the capacitance is also large, Hence, the total capacitance is eventually increased so that IC realization is difficult.In this paper, a new SC filter configuration is proposed in which the coefficients of the transfer function of the SC transversal filter is rearranged in the order of magnitude and the ratio of the neighboring coefficients is used as the normalized capacitance (ratio to the capacitance of the operational amplifier for coefficient multiplication) of the coefficient capacitors. According to the proposed configuration, the spreading of the capacitance ratio and the total capacitance can be reduced significantly. Since the coefficient ratio of the transfer function is used, there is concern that the characteristic degradation by the element deviations might be larger than the one in the conventional SC transversal filter.It is shown by the element sensitivity analysis and the numerical example that the characteristic variation of the cascaded SC filter by the present configuration is smaller than the one in the conventional cascaded SC filter in which the basic block is made of SC transversal filters and, therefore, there is no problem in practice. Finally, a test result is presented for an SC transversal filter using a third‐order transfer function coefficient ratio.