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PCM63P-1 Datasheet(PDF) 9 Page - Texas Instruments |
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PCM63P-1 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 11 page 9 ® PCM63P for both if no immediate improvement were noted). This procedure would require the generation of the digital bit-2 major carry code to the input of the PCM63P and a DVM or oscilloscope capable of reading the output voltage for a one LSB step (5.72 µV) in addition to a distortion analyzer. A more practical approach would be to forego the minor correction for the bit-2 major carry adjustment and only adjust for upper and lower DAC gain matching. The prob- lem is that just by connecting the MSB circuitry to the PCM63P, the odds are that the upper and lower bit-2 weights would be greatly changed from their unadjusted states and thereby adversely affect the desired gain adjustment. Just centering the 100k Ω potentiometers would not necessarily provide the correct starting point. To guarantee that each 100k Ω potentiometer would be set to the correct starting or null point (no current into or out of the MSB adjust pins), the voltage drop across each corresponding 330k Ω resistor would have to measure 0V. A voltage drop of ±1.25mV across either 330k Ω resistor would correspond to a ±1LSB change in the null point from its unadjusted state (1LSB in current or 3.81nA x 330k Ω = 1.26mV). Once these starting points for each potentiometer had been set, each potentiometer would then be adjusted equally, in opposite directions, to achieve the lowest full-scale THD+N possible. If no imme- diate improvement were noted, the direction of rotation for both potentiometers would be reversed. One direction of potentiometer counter-rotations would only make the gain mismatch and resulting THD+N worse, while the opposite would gradually improve and then worsen the THD+N after passing through a no mismatch point. The determination of the correct starting direction would be arbitrary. This proce- dure still requires a good DVM in addition to a distortion analyzer. Each user will have to determine if a small improvement in full-scale THD+N for their application is worth the expense of performing a proper MSB adjustment. APPLICATIONS The most common application for the PCM63P is in high- performance and professional digital audio playback, such as in CD and DAT players. The circuit in Figure 6 shows the PCM63P in a typical combination with a digital interface format receiver chip (Yamaha YM3623), an 8x interpolating digital filter (Burr-Brown DF1700P), and two third-order low-pass anti-imaging filters (implemented using Burr-Brown OPA2604APs). Using an 8x digital filter increases the number of samples to the DAC by a factor of 8, thereby reducing the need for a higher order reconstruction or anti-imaging analog filter on the DAC output. An analog filter can now be constructed using a simple phase-linear GIC (generalized immittance converter) architecture. Excellent sonic performance is achieved using a digital filter in the design, while reducing overall circuit complexity at the same time. Because of its superior low-level performance, the PCM63P is also ideally suited for other high-performance applications such as direct digital synthesis (DDS). |
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Similar Description - PCM63P-1 |
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