Design of an Area-Efficient Interpolated FIR Filter Based on LUT Partitioning
نویسندگان
چکیده
With the on-going research to introduce multimedia capabilities into digital mobile communication systems, communication standards specify the use of enabling technologies such as the 3-channel W-CMDA mobile station modulator [1]. Pulse-shaping 1:4 interpolated FIR filters are employed in each band-limited Quadrature Phase Shift Keying (QPSK) modulator to provide in-band spectral shaping while minimizing intersymbol interference (ISI) [2],[3]. Each channel of QPSK modulator requires filtering operation for in-phase (I data) and quadrature-phase (Q data) signal components of the input data stream [4]. Hence, a total of six band-limited FIR filters are needed in the 3-channel W-CDMA modulator. A FIR filter using the transversal computation structure [5] adopts a polyphase structure to effectively pipeline the input data streams across a register chain prior to performing the main filtering operation. Despite the simplicity of the structure, it requires a prohibitively large number of registers, and incurs area overhead due to the added complexity involved with the pipeline structure [6]. An alternative FIR filter structure suitable for highspeed filtering employs the LUT for the core filtering operation. All possible filter outputs are pre-calculated and tabulated in memory for any input transition patterns. The input data stream constitutes the address to the LUT, and therefore evaluations of the filter output samples are carried out by simply reading-off constant values; slower dedicated arithmetic operations are substituted by a faster memory reference. LUT-based FIR filter designs have widely been implemented with ROM-based LUTs or hardwired LUTs [7]. A single chip implementation using ROM-based LUTs requires large area, power consumption, and added fabrication complexity. The ROM-based LUT occupies about 99% of the area of the entire filter design due to a large number of transition patterns; hence any area optimizations in the filter design center on a more compact LUT design. To overcome the drawbacks of the ROM-based LUTs, the table is hardwired as in the popularly used single-architecture dual-channel filter [7]. However, the hardwired LUT still occupies about 60% of the total area, necessitating further area reductions. Design of an Area-Efficient Interpolated FIR Filter Based on LUT Partitioning
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