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TDA8046H データシート(PDF) 11 Page - NXP Semiconductors |
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TDA8046H データシート(HTML) 11 Page - NXP Semiconductors |
11 / 48 page 1996 Nov 19 11 Philips Semiconductors Product specification Multi-mode QAM demodulator TDA8046 7.1.2 EQUALIZER This function is realized with a T spaced 12 or 14 taps (selected via the I2C-bus) adaptive filter with a feedback part. The equaliser is based on a Decision Feedback Equalizer (DFE) structure with Least Mean Square (LMS) coefficient updating algorithm. No training sequence is required. The block schematic of the total equalizer is shown in Fig.8. The main tap of the equalizer is adjustable for fine AGC function (6 dB AGC range). The settings of the equalizer taps can be read via the I2C-bus. If the equalizer diverges, an alarm bit is set (I2C-bus bit ALEQ) and an automatic reset of the taps can be performed (I2C-bus bit EAR). To improve acquisition time, the convergence steps of the FFE/DFE parts of the equalizer are programmable via the I2C-bus. When the system locks, the steps are automatically modified for optimum performances. Besides reading the equalizer tap values, the main tap of the equalizer can also be programmed. After setting the main tap, the other coefficients can be set to zero. The equalizer settings can also be frozen via the I2C-bus. The equalizer has been proven to work correctly under bad channel conditions as indicated in Table 1. It is guaranteed that all loops (including equalizer) converge at a SNR of 21 dB for a 64-QAM modulation format and 27 dB for a 256-QAM modulation format. Table 1 Channel echo profile Figure 7 represents the QAM spectrum seen by the equalizer. It corresponds (in the frequency domain) to the multiplication of a full nyquist spectrum by the impulse response of the channel specified in Table 1. DELAY AMPLITUDE PHASE 3 ⁄8 × Tsym 0.08 130 ° 11 ⁄8 × Tsym 0.20 60 ° 2 × Tsym 0.05 310 ° 45 ⁄8 × Tsym 0.10 200 ° 67 ⁄8 × Tsym 0.03 200 ° Fig.7 QAM spectrum with echo profile as seen by the equalizer. handbook, full pagewidth 1 −11 −0.5 0.5 relative frequency relative gain (dB) −0.375 0.375 −0.125 0.125 −0.25 0.25 0 −3 −5 −9 −1 −7 MGD636 ( f ) rs |
同様の部品番号 - TDA8046H |
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同様の説明 - TDA8046H |
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