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Using an Electrical Idle Link State for Power Reduction in PCI-E (PCI Express) and Similar Standards

IP.com Disclosure Number: IPCOM000034013D
Publication Date: 2005-Jan-11
Document File: 3 page(s) / 46K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that enhances the power-saving feature of the electrical idle link state by intelligently shutting down parts of the receive path while the idle is detected at the receiver.

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Using an Electrical Idle

Link

State

for Power Reduction in PCI-E and Similar Standards

Disclosed is a method that enhances the power-saving feature of the electrical idle link state by intelligently shutting down parts of the receive path while the idle is detected at the receiver.

Background

PCI-E is a high-performance general purpose I/O interconnect that will probably become an industry standard, like its predecessor the PCI. Within the PCI-E specification is an electrical idle link state, which is when the differential transmit or receive pairs are in common mode. This state is also known as squelch. This state is part of the protocol and indicates a shift into power save modes (such us L0s or L1). In this specification, the mode contributes to power conservation by allowing the transmit output driver not to charge the interconnect (i.e. decoupling capacitors) while the link is idle.

Note. The above description is applicable to other similar standards that also have an electrical idle link state or equivalent link state.

General Description

The disclosed method enhances the power saving feature of the electrical idle link state by intelligently shutting down parts of the receive path while electrical idle is detected at the receiver. The receive path is composed of many circuits, including:

§         Time-Recovery DSP block - analyzes receive data, extracts and computes the needed phase shifts to enable correct data sampling

§         Analog receiver - high speed comparators, FF’s and amplifiers which sample the differential pairs

§         Phase-Interpolator/VCO - analog block which shifts the receive-clock according to controls from Time-Recovery

§         Deserializer - transforms serial data stream into parallel data words

§         Squelch detector – detects electrical idle on the receive differential pairs and produces the electrical idle indication

§         Miscellaneous – Voltage regulators, Bias, PLL etc .

While the exact micro architecture might differ from product to product, all implementations need to preserve all of the above basic functions. Since the PCI-E wire speed is 2.5GHz, most of the recei...