This paper proposes a high-speed FFT processor for orthogonal frequency-division multiplexing (OFDM) systems. The proposed architecture uses a single-memory for a small hardware size and uses a radix-4 algorithm for high speed. Its memory is partitioned into four banks for high-speed computation. It uses an in-place memory strategy that stores butterfly outputs in the same memory location used by butterfly inputs. The architecture has been modeled by VHDL and logic synthesis has been performed using the SamsungTM 0 . 5~ SOG cell library (KG80). The implemented FFT processor consists of 98,326 gates excluding RAM. The processor can operate at 42MHz and calculate a 256-point complex FFT in 6ps.
Blue-emitting CaMgSiO:Ce (0.0 ≤ x ≤ 1.0) phosphors were successfully synthesized and characterized. Rietveld refinement revealed that four main phases exist within the solid-solution range of CaO-MgO-SiO, namely, β-CaSiO (Mg (x) = 0.0), CaMg(SiO) (Mg (x) = 0.25), CaMg(SiO) (Mg (x) = 0.5), and CaMgSiO (Mg (x) = 1.0). The variation of the IR modes was more prominent with increasing Mg content in the CaMgSiO materials. The sharing of O atoms of the SiO-tetrahedra by the MgO-octahedra induced weakening of the Si-O bonds, which resulted in the red shift of the [SiO] internal modes and appearance of a Mg-O stretching vibration at ∼418 cm. Raman measurement revealed that the change of the Ca-O bond lengths because of the Mg-substitution directly reflected the frequency shift of the Si-O stretching-Raman modes. Notably, the thermal stability of CaMgSiO:Ce (Mg (x) > 0.0) phosphors was superior to that of β-CaSiO:Ce (Mg (x) = 0.0) as confirmed by temperature-dependent photoluminescence (PL) measurements. This indicated that Mg ions play an important role in enhancement of the thermal stability. In combination with the results from PL and electroluminescence (EL), it was elucidated that the luminous efficiency of CaMgSiO:Ce (Mg (x) = 0.1) was approximately twice as much as β-CaSiO:Ce (Mg (x) = 0.00), directly indicating a "Mg-substitution effect". The large enhancements of PL, EL, and thermal stability because of Mg-substitution may provide a platform in the discovery of more efficient phosphors for NUV-LEDs.
The paper proposes a fast Fourier transform (FFT) processor using a new in-place strategy and the mixed-radix algorithm. The proposed processor uses only two N-word memories for a continuous flow FFT implementation due to the new in-place strategy, while exiting continuous FFT processors use four N-word memories. In addition, the proposed processor satisfies both small area and real-time processing requirement. The gate count of the processor is 37,000 and the number of clock cycles is 640 for a 512-point FFT. Hence, the proposed FFT processor can reduce the gate count and memory size Compared with existing FFT processors.
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