Equalization of Mid-Frequency Power Supply Noise via a Spectrum-Shaping Encoder for Parallel Buses

Noise from the simultaneous switching of outputs (SSO) creates a significant problem for high-speed parallel buses that use single-ended signaling. Further exacerbating this problem is the fact that many single-ended interfaces share the return path of numerous signals with the same power delivery network (PDN) used to power the I/O transceiver circuitry. These single-ended interfaces share power and ground conductors in an effort to reduce the cost associated with package pin count and chip pad area. In addition to creating low-cost interfaces, there is a need for performance enhancing techniques that are "interface compatible", which helps to ease their adoption. This paper introduces a new concept in bus coding that shapes the spectrum of aggregate bus current in an effort to "equalize" the induced voltage response of a power supply. The single-ended buses discussed in this paper are those used in the industry standard interfaces of today's graphics systems, and possibly the interfaces that may be used in future generations of main memory.