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CAP3001A Scheda tecnica(PDF) 7 Page - Micronas |
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CAP3001A Scheda tecnica(HTML) 7 Page - Micronas |
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7 / 37 page  CAP 3001 A MICRONAS INTERMETALL 7 After buffering (ABUF) and switching (AMUX) in the AF- mode the signals are converted into digital form by 2 A/D converters (ADCs). Their output is 1 bit at a rate of 8.208 MHz; in each of the two channels in the CAP 3001 A there is a cascade of 3 lowpass filters (LPF02, LPF23 and LPF34), which suppresses the high-frequency noise produced by the ADCs. The outputs of the filters LPF34 are 16 bits wide and are sampled with 38 kHz; these samples are transmitted via the input buffer to the DSP core. After processing in the DSP, the samples are interpolated to the eightfold sampling rate and converted into analog shape by 2 D/A converters (DACs), filtered (ALPF) and optionally attenuated (AVOL) to feed the power amplifiers which produce the signals for four loud- speakers. It is assumed that the process of stereo multiplexing used in radio broadcasting is known. The main FM-mod- ulator can be modulated by the sum signal of left and right channel (in baseband), a pilot tone, the difference channel (AM-modulated, suppressed carrier), an op- tional ARI signal (AM-modulated, unsuppressed carrier) and optionally up to 3 SCA signals (FM-modulated). The composite signal is the so-called MPX signal. So a vari- ety of signals ride “piggy-back” on the main carrier, which was originally assigned only for monophonic transmission. In the CAP 3001 A, the SCA signals are regarded as disturbing signals while the others are re- garded as useful. In the MPX-mode there is an analog mixer AMIX in front of the ADCs. It mixes the difference band down to base- band. The sum channel and the difference channel are then treated like the other baseband signals. Digital quadrature mixers ARIMX and PILMX extract the ARI- information and the information of the pilot signal, re- spectively. By means of digital mixers the pilot tone and the ARI sig- nal are mixed down to zero intermediate frequency in quadrature representation, where their information is sampled and sent to the DSP core. The demodulation of the ARI signal is done by the DSP software. The band- width of this ARI channel is sufficient to allow demodula- tion of an RDS (Radio Data System) signal by DSP soft- ware as well. Beside these main blocks, there are other systems. The analog field strength information FS deliv- ered by AM and FM tuners is A/D-converted; after low- pass-filtering (LPF06) the samples are sent to the DSP core, where the information could be used to control some parameters of the entire system. Other input sig- nals, such as signals from an external microphone and from external potentiometers are selected by an analog multiplexer, A/D-converted, lowpass-filtered and sent to the DSP or to the controller via the IM-bus interface (IMIF). The IM-bus interface is also able to receive data from the external microcontroller and to control the sys- tems on the CAP 3001 A. 2.1.5. Analog Input Systems Fig. 2–3 shows all analog inputs and functions of the switches S0 to S3. MPX0 AML TAPEL AUXL AMR TAPER AUXR MPX1 POT2 POT3 POT4 POT5/ AVC FMLEVEL MPLEVEL AMLEVEL Main 1 Main 2 ARI/RDS Pot Level S0 S0 S2 S3 S1 0 1 2 3 0 1 2 3 0 1 0 1 2 3 4 5 0 1 2 1 0 S4 Fig. 2–3: Analog input systems 420 to 430 kHz 38 kHz POT1/ 2.1.6. Buffers ABUF The analog input buffers have to adjust the individual de- sired input levels in order to cover the entire volume range of the A/D-converters. The inputs can be divided into two groups: those which have to be connected via external capacitors, and those that are DC-coupled. One of these inputs, the POT5/ AVC-input, uses the same pin, but is DC-coupled if used as POT5, and AC-coupled if used as AVC. Note: Input pins POT2 to POT5 are switchable to digital outputs via the IM-bus interface. This feature is made possible by open drain transistors and external pull-up resistors down to 1 k Ω. |
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