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73M1903-IVT/F 参数 Datasheet PDF下载

73M1903-IVT/F图片预览
型号: 73M1903-IVT/F
PDF下载: 下载PDF文件 查看货源
内容描述: 调制解调器模拟前端 [Modem Analog Front End]
分类和应用: 调制解调器消费电路商用集成电路光电二极管
文件页数/大小: 46 页 / 530 K
品牌: TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
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73M1903 Data Sheet  
DS_1903_032  
5.1 Transmit Levels  
The 16-bit transmit code word written by the DSP to the Digital Sigma-Delta Modulator (DSDM) (via TIF)  
has a linear relationship with the analog output signal. So, decreasing a code word by a factor of 0.5 will  
result in a 0.5 (-6 dB) gain change in the analog output signal.  
The following formula describes the relationship between the transmit code word and the output level at  
the transmit pins (TXAP/TXAN):  
Vout (V) = 2 * code/32,767 * DSDMgain * dacGAIN * VREF * TLPFgain * SMFLTgain * FreqFctr  
Vout is the differential peak voltage at the TXAP and TXAN pins.  
Code is the 16-bit, two’s compliment transmit code word written out by the DSP to the DSDM (via TIF).  
The code word falls within a range of ± 32,767. For a sinusoidal waveform, the peak code word should  
be used in the formula to obtain the peak output voltage.  
DSDMgain is the scaling factor used on the transmit code word to reduce the possibility of saturating the  
modulator. This value is set to 0.640625(–3.555821 dB) at dc in the 48 tap transmit interpolation filter  
(TIF) that precedes DSDM.  
dacGAIN is the gain of the DAC. The value dacGAIN is calculated based on capacitor values inside  
DAC1 and dacGAIN=8/9=0.8889. The number 32,767 refers to the code word that generates an 82%  
“1’s” pulse density at the output of the DSDM. As one can see from the formula, the D to A conversion is  
dependent on the level of VREF. Also when TXBST1 bit is set, VREF is increased from 1.36 V to 1.586 V  
to allow higher transmit level or 16.6% increase in gain. This bit is intended for enhancing the DTMF  
transmit level and should not be used in data mode.  
TLPFgain is the gain of TLPF and nominally equals to 0.00 dB or 1.0.  
SMFLTgain is the gain of SMFLT and nominally equal to 1.445 or 3.2 dB.  
When TXBST0 bit is set, the gain is further increased by 1.65 dB (1.21) for the total of 4.85 dB. This is to  
accommodate greater hybrid insertion loss encountered in some applications.  
FreqFctr shows dependency of the entire transmit path on frequency. See Figure 10.  
With the transmit code word of +/- 32,767, the nominal differential swing at the transmit pins at dc is:  
Vout (V) = 2 * code/32,767 * DSDMgain * dacGAIN * VREF * TLPFgain * SMFLTgain * FreqFctr  
= 2 * 32,767/32767 * 0.6640625 * 0.8889 * 1.36 * 1.0 * 1.4454 * 1.0 = 2.31Vpk diff.  
When TXBST1 bit is set, Vout (V) = 1.166 * 2.31= 2.693 Vpk diff.  
When TXBST0 bit is set, Vout (V) = 1.21 * 2.31= 2.795 Vpk diff, if not limited by power supply or internal  
reference.  
When both TXBST1 and TXBST0 are set to 1, Vout (V) = 1.166 * 1.21 * 2.31 = 3.259 Vpk diff.  
22  
Rev. 2.0