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Low-Current Fusing Control/Simulation for ASICs without SPI

IP.com Disclosure Number: IPCOM000019685D
Original Publication Date: 2003-Oct-25
Included in the Prior Art Database: 2003-Oct-25
Document File: 9 page(s) / 446K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Currently, to simulate and verify the consequences of fusing (parameter adjustment) of an ASIC (Application-Specific Integrated Circuit) prior to making the necessary physical cuts of the fuses to make the adjustment permanent, a SPI (Serial Peripheral Interface) is used. This means that a test pattern must be loaded into the SPI at a special reserved address in order to observe the effect of the loaded test pattern. One disadvantage of this method is that sometimes an ASIC concept may not need a SPI for normal functional activities. Furthermore, each fuse requires a pull-down current source to define the voltage level at the output when the fuse is cut. When a fuse has not been cut, this pull-down current source contributes to the ASIC's current consumption during operation. If an ASIC concept has many possible stages of fusing with many individual fuses in total, the current consumption of the sample during operation is much greater than designed, and compared to its fellow samples where fusing has occurred. To avoid the use of an ASIC SPI, we propose to incorporate a dedicated shift register for the input of the test (adjustment) pattern to be simulated against the change in the physical parameters to be adjusted. After the physical parameter has been measured and a test pattern has been calculated to give the necessary adjustment, the test pattern is loaded into the shift register, and then finally the parameter is re-measured to confirm that the adjustment meets the expectation. Once the correct test pattern for a given sample is determined, the fuses in this sample can be cut and the adjustment becomes permanent.

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© SIEMENS AG 2003 file: ifx_2003J52652.doc page: 1

Low-Current Fusing Control/Simulation for ASICs without SPI

Idea: Geoffrey Acres, AT-Villach; Leo Aichriedler, AT-Villach

Currently, to simulate and verify the consequences of fusing (parameter adjustment) of an ASIC (Application-Specific Integrated Circuit) prior to making the necessary physical cuts of the fuses to make the adjustment permanent, a SPI (Serial Peripheral Interface) is used. This means that a test pattern must be loaded into the SPI at a special reserved address in order to observe the effect of the loaded test pattern. One disadvantage of this method is that sometimes an ASIC concept may not need a SPI for normal functional activities. Furthermore, each fuse requires a pull-down current source to define the voltage level at the output when the fuse is cut. When a fuse has not been cut, this pull- down current source contributes to the ASIC's current consumption during operation. If an ASIC concept has many possible stages of fusing with many individual fuses in total, the current consumption of the sample during operation is much greater than designed, and compared to its fellow samples where fusing has occurred.

To avoid the use of an ASIC SPI, we propose to incorporate a dedicated shift register for the input of the test (adjustment) pattern to be simulated against the change in the physical parameters to be adjusted. After the physical parameter has been measured and a test pattern has been calculated to give the necessary adjustment, the test pattern is loaded into the shift register, and then finally the parameter is re-measured to confirm that the adjustment meets the expectation. Once the correct test pattern for a given sample is determined, the fuses in this sample can be cut and the adjustment becomes permanent.

The problem of the high pull-down current source consumption is solved by loading the states of the fuses after the power-up of the ASIC or after any interruption in supply of the ASIC. Once the data from the fuses is safely stored, the pull-down current sources are switched off, and thus their current consumption eliminated from that of the rest of the ASIC. This therefore allows more uniform levels of current consumption from sample-to-sample, since in all cases there are no varying numbers of pull- down sources contributing to the current consumption.

The advantages of this solution are:

- Fusing and simulation facility on an Automatic Test Equipment (ATE) can be included in an ASIC without SPI for system functionality

- Fusing functions add no current consumption to overall ASIC consumption

- Fusing simulation circuitry cannot disturb the operating point of an ASIC once permanent cuts are made

- Functional evaluation of operating point of the system can be undertaken prior to any simulation data being loaded, at its ,raw' operating point (zero adjustment).

Figure 1 illustrates the three sections that take part in this simulation concept. A...