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TDA1549T Fiches technique(PDF) 7 Page - NXP Semiconductors |
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TDA1549T Fiches technique(HTML) 7 Page - NXP Semiconductors |
7 / 20 page August 1994 7 Philips Semiconductors Objective specification Stereo 4fs data input up-sampling filter with bitstream continuous calibration DAC (BCC-DAC1) TDA1549T Continuous calibration DAC The stereo 5-bit DAC uses the dynamic continuous calibration technique. The DAC currents (16 sources and 16 sinks) of each channel are repeatedly generated from one single reference current. This duplication is based on an internal charge storage principle and has an inherently high accuracy which is insensitive to ageing, temperature and process variations. Figure 4 shows one such current calibration source. During calibration the cell is connected to the reference current sink Iref via switch S2. The calibration transistor M1 is connected as an MOS diode via the switch S1 forcing its gate potential to assume a value so that the total current of the calibration cell is equal to the reference current. After calibration the gate of M1 is allowed to float. The gate capacitance Cgs retains its potential and the current through the cell remains exactly equal to the reference current. This current is now connected to the output. Each digital-to-analog current source and each current sink is calibrated precisely in this way. Operational amplifiers High precision, low-noise amplifiers together with the internal conversion resistors RCONV1 and RCONV2 convert the DAC output current to a voltage capable of driving a line output. This voltage is available at VOL and VOR (1.5 V RMS typical). Connecting external capacitors CEXT1 and CEXT2 between FILTCL and VOL and FILTCR and VOR respectively, provides the required 1st-order post-filtering for the left and right channels (see Fig.1). The combinations of RCONV1 with CEXT1 and RCONV2 with CEXT2 determine the 1st order fall-off frequencies. Internal reference circuitry Internal reference circuitry ensures that the output voltage signal is proportional to the supply voltage, thereby maintaining maximum dynamic range for supply voltages from 3.8 to 5.5 V and making the circuit also suitable for battery-powered applications. Fig.3 Filter and noise shaper characteristics. |
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Description similaire - TDA1549T |
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