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TDA8205 Arkusz danych(PDF) 3 Page - STMicroelectronics |
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3 / 8 page carrier without disruption due to the modulation. Dual frequency operation is made possible by syn- thesising the carrier reference frequency thus sav- ing the need for two extra crystals. Dual VCXO can also be software selected (SYN bit of CR3 in TDA8204) with external crystal (Pin XC1/XC2) for new standards. Selection between XC1 and XC2 is done with bit "IBG" in CR3 register of TDA8204 (IBG = 0 XC1 selected, IBG = 1 XC2 selected). The standards switch controls operation of the QSPK demodulator at either 6.552MHz or 5.85MHz. This can be controlled via the I 2C bus or the decoder set into automatic mode in which it determines the standard by alternately trying to lock to the two systems. On chip low pass filters recover the in-phase and quadrature data channels which are then sliced by comparators. The symbol clock is recovered from this data and used to sample and re-time it. The two data channels are then decoded and serialized to obtain the NICAM-728 data which is then passed on to the NICAM decoder in the TDA8204. After processing the NICAM into a digital bit-stream in the TDA8204, the data is passed back to the TDA8205 for the analog functions of the DACs to be performed. Conversion of the pulse width modulated bit streams to analog takes place and is followed by low pass filtering which removes high frequency quantising noise and performs J-17 de-emphasis. The DACs signal level can be adjusted to match the reserve sound signal level. 1VRMS maximum on Pins LFIL1/RFIL1 can be ob- tained by selection of appropriate resistor on Pin RG. Once the analog audio has been recovered, certain source switch functions are performed. If the NI- CAM signal fails and if the reserve sound flag (C4), of SRO register, is set the reserve sound switch automatically selects Mono Audio Input. If the re- serve sound flag (C4) is reset, the reserve sound switch will not change and the audio outputs will be muted (DAC outputs muted). If the NICAM signal only carries data, Mono Audio Input is selected. The reserve sound switch can be forced to select Mono Audio Input via I 2C bus, using Bit FS0 = 1 and FS1 =0 of CR3 Register. This can be used in the case of NICAM marginal reception. To select Stereo Left and Right Audio Input Bit FS0 = 0 and FS1 = 1 of CR3 Register must be selected. The outputs from this reserve sound switch are available on Audio mutable output left and right, and are internaly connected to the audio matrix. A simple audio switching matrix is provided inter- nally for flexible control over the audio source and destination selection. Audio signal left and right coming from the reserve sound switch and the external audio input left and right can be switched to the audio outputs left and right . DAC and auxiliary audio outputs can be muted. An additional +6dB gain can be applied to raise the output levels to 2VRMS maximum. For more infor- m at ion s ee Sof t wa re Specification chap- ter (III.5.3/TDA8204). The DAC outputs are automatically muted under the following conditions - loss of frame alignement - the bit error rate (Ber) is > error rate limit - NICAM signal is conveying M1 only. The right DAC is muted unless M1 has been selected to be on both DAC outputs. - NICAM signal is conveying data only. For test purposes, the DAC outputs can be un- muted by forcing the bi-directional mute Pin 25 of TDA8204 or via I 2C bus. ABSOLUTE MAXIMUM RATINGS Symbol Parameter Value Unit VCC Supply Voltage 15 V VDD Supply Voltage 7 V Ptot Total Power Dissipation 1.2 W Toper Operating Temperature Range 0, + 70 oC Tstg Storage Temperature Range -20, + 150 oC THERMAL DATA Symbol Parameter Value Unit Rth (j-a) Thermal Resistance Junction-Ambient Max. 67 oC/W TDA8205 3/8 |
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