Variable digital filters are useful for various signal processing and communication applications where the frequency characteristics, such as fractional delays and cutoff frequencies, can be varied. In this paper, we propose a design method of variable FIR digital filters with an approximate linear phase characteristic in the passband. The proposed variable FIR filters have some large attenuation in stopband and their large attenuation can be varied by spectrum parameters. In the proposed design method, a quasi-equiripple characteristic can be obtained by using an iterative weighted least square method. The usefulness of the proposed design method is verified through some examples., {"references":["C. K. S. Pun, S. C. Chan, K. S. Yeung, and K. L. Ho, \"On the design\nand implementation of FIR and IIR digital filters with variable frequency\ncharactericstics,\" IEEE Trans. Circuits Syst. II, Analog Digit. Signal\nProcess., vol. 49, no. 11, pp. 689.703, Nov. 2002.","L. R. Rabiner and B. GoldÔÇó ÔÇó\"Theory and application of digital signal\nprocessing,\" Prentice-HallÔÇó ÔÇóNew JerseyÔÇó ÔÇó1975.","T. Shinbo, Y. Sugita, N. Aikawa, T. Kimura, Y. Wakasa, and T. Morichi,\n\"Design Method of FIR Filters with Variable Piecewise Stopband,\"\nIEICE Trans. Fundamentals (Japanese Edition), Vol. J87-A, No. 12,\npp.1511-1517, Dec. 2007.","S. Takahashi, N. Aikawa, Y. Wakasa, and M. Nakatani, \"FIR Filters with\nVariable Stopbands,\" IEICE Trans. Fundamentals (Japanese Edition),\nVol. J90-A, No. 10, pp.767-770, Oct. 2007.","T. Takahashi, T. Miyata, and N. Aikawa, \"An Iterative WLS Chebyshev\nApproximation method for the Design of FIR Digital Filters with\nVariable Stopbands,\" IEICE DSP Symposium, B3-1, Nov. 2008.","J. -C. Liu and S. -J. You, \"Weighted Least Squares Near-equiripple\nApproximation of Variable Fractional Delay FIR Filters,\" IET Signal\nProcessing, Vol. 1, no. 2, June 2007.","T. B. Deng, \"An improved method for designing variavle recursive\ndigital filters with guaranteed stability,\" Signal Processing, vol. 81, pp.\n439-446, 2001.","W. R. Lee, L. Caccetta, and V. Rehbock, \"Optimal Design of All-Pass\nVariable Fractional-Delay Digital Filters,\" IEEE Transaction on Circuits\nand Syatems-I: Regular Papers, Vol. 55, no. 5, June 2008.","L. J. Karam and J. H. McClellan, Complex approximation for FIR filter\ndesign, IEEE Trans. Circuits and Systems, vol. CAS-42, no.3, pp.207-\n244, April 1995.\n[10] W.-S. Lu, Minimax design of nonlinear-phase FIR filters: A least-pth\napproach, Proc. of 2002 IEEE International Symposium on Circuits and\nSystems, vol. 1, pp. 409-412, May 2002.\n[11] Yong Ching LimÔÇó ÔÇóJu-Hong LeeÔÇó ÔÇóC.K. Chen, and Rong-Huan YangÔÇó ÔÇó\"A\nWeighted Least Squares Algorithm for Quasi-Equiripple FIR and IIR\nDigital Filter Design,\" IEEE Trans. Signal Processing, Vol.40, No. 3,\npp.551-558, Mar., 1992.\n[12] S. -C. Pei and J. -J. Shyu, \"Design of Arbitrary Complex Coefficient FIR\nDigital Filters by Complex Weighted Least Squares Approximation,\"\nIEEE Trans. on Circuits and Systems-II: Analog and Digital Signal\nProcessing, vol. 41, no. 12, pp. 817-820, Dec. 1994.\n[13] T. B. Deng, \"Weighted least-squares method for designing arbitrarily\n1-D FIR digital filters,\" Signal Processing, vol. 80, pp. 597-613, 2000.\n[14] C. Sidney, J. A. Barreto, and I. W. Selesnick, \"Iterative Reweighted\nLeast-Squares Design of FIR Filters,\" IEEE Trans. on Signal Processing,\nvol. 42, no. 11, pp. 2926-2936, Nov. 1994.\n[15] A. S. Rukhlenko, \"Iterative WLS Design of SAW Bandpass Filters,\"\nIEEE Trans. on Ultrasonics, Ferroelectrics, and Frequency Control, vol.\n54, no. 10, pp. 1930-1935, Oct. 2007."]}