- 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 on the Performance of Semiconductor Switches with the Single-Chip Analog AVR LSI
Akin to the opamps, there is tradeoff between the level of integration and the size of switches. Smaller transistors pairs that make up the switches have higher resistance, which can result in more distortion.
Transistor switch resistance is also proportional to power supply voltage. The power supply voltage of the LSI chip has been reduced to half of what an SSI set of switches can support (±15 V). Lower voltage on the switch pair reduces the pair's effective resistance. In the Funk preamp reviewed on this site, the voltage on the switches was increased to ±20 V to reduce distortion further at the risk of exceeding the recommended maximum voltage for the SSI switch parts and reducing the lifetime of the product.
Combining the issues of the opamp and semiconductor switch performance degradation, the distortion of the LSI chip is 4 – 10 times larger than what can be achieved with an SSI solution. The LSI chip typical distortion is in the 15.5– 16 bit equivalent range. This drops by 3 bits worst case. SNR performance is, however, better than expected at 20 – 20.5 bit equivalent typical with a 2 bit drop worst case. The best implementation I found in a Pre/Pro using SSI parts produced an SNR about a bit equivalent better than this for both typical and worst case values.