Technical & Editorial
- Written by Dr. David A. Rich
- Published on 23 September 2013
- AVR - Audio Video Receiver - Build Quality: Part I
- Page 2: Understanding DAC Specifications
- Page 3: Digital Reconstruction Filter
- Page 4: Number of DACs per Chip
- Page 5: Improved Distortion and Noise Performance with Balanced DAC Output
- Page 6: Enhanced Distortion Performance with Current Mode DACs
- Page 7: Multiple DACs Combined to Produce a Single Channel
- Page 8: Chart Presenting Build DACs used in AVRs Across Manufacturers and Price
- Page 9: The Right Side of the Chart: More Details about the AVRs and Pre/Pros
- Page 10: The concept of Effective Bits
- Page 11: Single Chip Analog AVR LSI
- Page 12: Enhanced Performance with SSI Parts
- Page 13: Limitations of Operational Amplifier Performance with the Single Chip Analog AVR LSI
- Page 14: Limitations on the Performance of Semiconductor Switches with the Single-Chip Analog AVR LSI
- Page 15: Use of Relays to Achieve Better Performance
- Page 16: A Very Brief Look at Changes in Power Amps in AVRs
- Page 17: Conclusions
- All Pages
Limitations of Operational Amplifier Performance with the Single Chip Analog AVR LSI
Shoehorning these parts into one chip can limit performance because of size constraints. Power consumption of the opamp must be reduced to avoid overheating the LSI chip. The opamps in the LSI chips consume about half the current of a standalone audio opamp. The area of silicon taken by each opamp on the LSI chip must be reduced to fit them into the chip. Decreasing the size of an opamp and the current it consumes increases the noise of the opamp and causes more distortion, especially when driving resistor loads below 10 Ohm.
The power supply of the LSI chip decreases to ± 7 V, half of the standard value for analog audio chips. Doing so decreases the power consumption of the total chip by half, thereby permitting more parts to be placed in a single LSI chip. A smaller power supply provides less margin between the maximum signal swing of the signal at the output of the LSI chip and the power rails. The reduced headroom is another aspect of the LSI chip's design that increases distortion.
Process technology to produce an LSI analog chip differ from a process for SSI opamps. For example, MOS switches are not required. Some performance specifications for the individual bipolar transistor will be improved in the optimized opamp process. In turn, better measured performance from the opamp can be achieved than were it manufactured with LSI process technology. The typical process for opamps supports ± 15V.
The selection of specific opamps for optimal performance in an AVR is discussed in Part II of this article.
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