113D_1_EE113D_CR4_AC01

113D_1_EE113D_CR4_AC01 - 1998 Dr M Wer ter ELECTRICAL...

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( ELECTRICAL ENGINEERING 113L D igital Signal Processing Laboratory @ 1998, Dr. M. Werter Lect ure 3: Analog Interface Circuit Introduction In general, to implement real-time signal processing on a" DSP chip, there needs to be a procedure for real-world (analog) data to be provided in digital format to the DSP chip, and for t he DSP 's output results to be transferred into the outside real world. Naturally, this requires the use of analog-to-digital (A/D) and digital- to-anal og (D/ A) conversion circuits, which enable the DSP to deal with digital in formation for which it has been designed. The associated timing circuitry and the DSP instructions required to coordinate these activities form th e I/ O processing sub-system of a DSP sy ste m. All DSP systems have a similar sub-system which coordinates inpu t/output procedures . On the DSKplus board, the A/ D, D/A procedures, timing and synchr onization, and some analog pre-pro cessing are all h andl ed by the TLC320ACOl single-supply analog interface circuit (AIC) and its supportin g circuitry. All of t hese are c ontr olled by software directe d from the TMS320C542 main-bo ard DSP chip. Thus, input/ out put procedures simplify to "initialization" and "I /O handling" subr outines which the user has to progr am and execute on the host DSP . In this exper iment, we will investigate in detail two simple progr ams which implement the proced ur es menti oned above. Th e TLC320ACOI an alog int erface circuit The TLC320ACOI analog interface circuit (AIC) is an audio-band processor that provides an analog-to-digital and digital-to-analog input/output interface system on a single CMOS chip. A functional Block diagram of this chip is shown in figure 1.2. 1.2 Functional Block D iagram .. ONOUT -'--4 - -- -< I-' FCO FC1 DAC DAC Voo GND 0GT1. Yoo Th is analog int erf ace circuit (AIC) contains a 14-bit-resolution analog -to-digital converter (ADC), a 14-bit-resolution digi tal -to-analog converter (DAC), a band-pass anti-aliasing input fil te r (containing a cascade of a low-pass and high- pass filter), a low-pass o utp ut-reconstruction filter , a (sin x)/x output compensator, and a serial port for data and control transfer. The internal circuit configuration and performance parameters are determ ined by reading control in format ion int o eight available data registers. The register data sets up the device for a given mo de of operation and application. The major functions of the 'ACOI are: I) To convert (analog) audio-signal data to digital format by the ADC chann el 2) To provide the interface and cont rol logic to transfer data between its serial input and output terminals and a digital signal processor (DSP) or microporcessor 3) To convert received digital data back to an (analog) audio signal t hr ough the DAC channe l The anti-aliasing input low-pass filter is a switched-capacitor filter with a si xt h-order eIliptic ch ar acteristic. The high-pass filter is a single pole filter to preserve low-frequency response as the low-pass filter cutoff is adjusted . There is a third-order continuous-time (analog) filter that precedes the
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