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STLC7550TQF7 bảng dữ liệu(PDF) 6 Page - STMicroelectronics |
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STLC7550TQF7 bảng dữ liệu(HTML) 6 Page - STMicroelectronics |
6 / 17 page FUNCTIONAL DESCRIPTION 1 - TRANSMIT D/A SECTION The functions included in the Tx D/A section are detailed hereafter. 16-bit 2’s complement data for- mat is used in the DAC channel. 1.1 - Transmit Low Pass Filters The transmit low pass filter is basically an interpo- lating filter including a sinx/x correction. It is a combination of Finite Impulse Response filter (FIR) and an Infinite Impulse Response filter (IIR). The digital signal from the serial interface gets interpo- lated by 2, 3, 4, 5 or 6 x Sampling Frequency (FS) through the IIR filter. The signal is further interpo- lated by 32 x FS x n (with n equal to 2, 3, 4, 5, 6) through the IIR and FIR filter. The low pass filter is followed by the DAC. The DAC is oversampled at 64, 96, 128, 160, 192 x FS. The oversampling ratio is user selectable. 1.2 - D/A Converter The oversampled D/A converter includes a second order digital noise shaper, a one bit D/A converter and a single pole analog low-pass filter. The attenuation of the last output stage can be programmed to 0dB, +6dB or infinite. The cut-off frequency of the single pole switch-capacitor low- pass filter is : fc−3dB = OCLK 2 ⋅ π ⋅ 10 with OCLK = Oversampling Clock frequency. Continuous-time filtering of the analog differential output is necessary using an off-chip amplifier and a few external passive components. At least 79dB signal to noise plus distortion ratio can be obtained in the frequency band of 0.425 x 9.6kHz (with an oversampling ratio equal to 160). 2 - RECEIVE A/D SECTION The different functions included in the ADC channel section are described below. 16-bit 2’s complement data format is used in the ADC. 2.1 - A/D Converter The oversampled A/D converter is based on a second order sigma-delta modulator. To produce excellent common-mode rejection of unwanted sig- nals, the analog signal is processed differentially until it is converted to digital data. Single-ended mode can also be used. The ADC is oversampled at 64, 96, 128, 160 or 192 x FS. The oversampling ratio is user selectable. At least -85dB SNDR can be expected in the 0.425 x 9.6kHz bandwidth with a -6dBr differential input signal and an oversam- pling ratio equal to 160. 2.2 - Receive Low Pass Filter It is a decimation filter. The decimation is performed by two decimation digital filters : one decimation FIR filter and one decimation IIR filter. The purpose of the FIR filter is to decimate 32 times the digital signal coming from the ADC modulator. The IIR is a cascade of 5 biquads. It provides the low-pass filtering needed to remove the noise re- maining above half the sampling frequency. The output of the IIR will be processed by the DSP. 3 - CLOCK GENERATOR The master clock, MCLK is provided by the user thanks to a crystal or external clock generator (see Figure 1). The MCLK could be equal to 36.864MHz (MCM = 1). In that case thanks to the divider M x Q, the STLC7550 is able to generate all V.34bis and 56 Kbps sampling frequencies (see Table 1). When MCM = 0, the MCLK must be equal to the oversampling frequency : Fs x OVER (7546 mode). The ADC and DAC are oversampled at the OCLK frequency. OCLK is equal to the shift clock used in the serial interface. The MCLK frequency should be : MCLK = K x Sampling frequency Combination of M, Q and oversampling ratios al- lows to generate several sampling frequencies. Recommended values for classical modem appli- cations are as follow : Table 1 : Sampling Frequencies Generation F (kHz) FQ = 36.864MHz (1) FQ = 18.432MHz FQ = 9.216MHz M Q over M Q over M Q over 16.00 3 6 128 2 4.5 128 1 6 96 13.96 3 5.5 160 - - - - - - 13.71 3 7 128 1 7 192 1 7 96 12.80 3 6 160 2 4.5 160 1 4.5 160 12.00 3 8 128 2 6 128 1 6 128 11.82 3 6.5 160 - - - - - - 10.97 3 7 160 - - - - - - 10.47 4 5.5 160 2 5.5 160 1 5.5 160 10.29 4 7 128 2 7 128 1 7 128 9.60 4 6 160 2 6 160 1 6 160 9.00 4 8 128 2 8 128 1 8 128 8.86 4 6.5 160 2 6.5 160 1 6.5 160 8.23 4 7 160 2 7 160 1 7 160 8.00 4 6 192 2 6 192 1 6 192 7.20 4 8 160 2 8 160 1 8 160 Note : 1. Recommended value. STLC7550 6/17 |
Số phần tương tự - STLC7550TQF7 |
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Mô tả tương tự - STLC7550TQF7 |
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