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TESTING SIGNALS DERIVED FROM AN EXTERNAL CLOCK SIGNAL

IP.com Disclosure Number: IPCOM000009275D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-14
Document File: 2 page(s) / 69K

Publishing Venue

Motorola

Related People

Yoram Yeivin: AUTHOR [+2]

Abstract

This proposal relates to testing of circuits like memory controllers. As illustrated in Figure 1, the circuit often receives an external clock EXT (50% duty cycle). Internally, the circuit derives an internal clock INT (also 50% duty cycle) at twice the rate of EXT, and N=4 or more clock ticks TICK-n having phase- shifted on-times (e.g., 257% duty cycle). INT and TICK-n can be combined as defined by the user.

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MOTOROLA Technical Developments

TESTING SIGNALS DERIVED FROM AN EXTERNAL CLOCK SIGNAL

by Yoram Yeivin and Udi Bare1

INTRODUCTION

  This proposal relates to testing of circuits like memory controllers.

PROBLEM

  As illustrated in Figure 1, the circuit often receives an external clock EXT (50% duty cycle). Internally, the circuit derives an internal clock INT (also 50% duty cycle) at twice the rate of EXT, and N=4 or more clock ticks TICK-n having phase- shifted on-times (e.g., 257% duty cycle). INT and TICK-n can be combined as defined by the user.

  As illustrated in Figure 2, when looking exter- nally to the circuit, the combinations provide output signal A. Depending on an operation modes (e.g., modes 1 to 4) of the circuit, signal A toggles at dif- ferent time intervals (e.g., SPEC-n) from the rising edge of EXT.

  However, during manufacturing of the circuit, many options and combinations make testing of the SPEC-n intervals difficult and time consuming.

SOLUTION

  As illustrated in Figure 3, new intervals SPEC' are defined in relation to the rising edges of the internal TICKS. The test'equipment provides a test clock TEST having 4 times the rate of EXT. SPEC' have equally length. Knowing the time point at which each TICK-n starts, the distance SPEC (cf. Figure 2) can easily be calculated.

ADVANTAGES

  The test procedure can be simplified. For exam- ple, the number of timing'specifications (SPECS) for all signals and limitations to the number of test pat- terns can be re...