Technical & Editorial

AVR - Audio Video Receiver - Build Quality: Part I


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.