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Method for a source-synchronous XNOR strobe I/O with DFT

IP.com Disclosure Number: IPCOM000011521D
Publication Date: 2003-Feb-26
Document File: 2 page(s) / 72K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a source-synchronous XNOR strobe input/output (I/O) circuit with Design For Test (DFT) features. Benefits include a single data input path for functional mode and integrated AC/IO loopback (IO BIST) capability.

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Method for a source-synchronous XNOR strobe I/O with DFT

Disclosed is a method for a source-synchronous XNOR strobe input/output (I/O) circuit with Design For Test (DFT) features. Benefits include a single data input path for functional mode and integrated AC/IO loopback (IO BIST) capability.

Background

        � � � � � All chips using a double data rate (DDR) synchronous dynamic random access memory (SDRAM) interface require an internal circuit to latch data on the both edges of strobe signals. The conventional method requires complicated logic.

        � � � � � Most conventional DDR data strobe circuits require both a falling edge and rising edge flop to capture the distributed queue (DQ) data.

        � � � � � Because of the nature of analog circuits, the layout size of the delay locked loop (DLL) controlled fine delay block is significant. To sweep a window beyond half of the DLL_CLK, the slave fine delay block must have more delay cells than the master delay block, or the resolution of the delay cells is reduced. By adding a small coarse delay block, the finest resolution can be achieved on the slave fine delay block without increasing the layout size.� � �

Description

        � � � � � The disclosed method is a circuit added to a DDR distributed queuing system (DQS, data strobe) pad (see Figure 1). The circuit includes an XNOR gate. A DLL-controlled fine delay block delays the incoming data strobe signal to the center of the data valid window in functional mode. A coarse delay block places the incoming data strobe signal close to the data valid win...