Technical Articles and Editorials

AVR - Audio Video Receiver - Build Quality: Part I


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.