Models for Power-Aware Testing - Models in Hardware Testing - page 201

Fig. 7.14 . Note that using two clock trees driven by a slower clock (rather than a
single one) allows to further drastically reduce the clock power during scan testing.
The area overhead, which is due to the test clock module and the additional rout-
ing, is negligible. The proposed scheme does not require any further circuit design
modification and is very easy to implement. Therefore, it has a low impact on the
system design time and has nearly no penalty on the circuit performance. Further
details about this staggered clock scheme can be found in Bonhomme et al. 2001 ;
Girard et al. 2001 ).

7.6 Power-Aware Test Data Compression

Test Data Compression (TDC) is an efficient solution to reduce test data volume. It
involves encoding a test set so as to reduce its size. By using this reduced set of test
data, the ATE limitations, i.e., tester storage memory and bandwidth gap between
the ATE and the CUT, may be overcome. During test application, a small on-chip
decoder is used to decompress test data received from the ATE as it is fed into the
scan chains.
Although reducing test data volume and test application time, TDC increases
test power during scan testing. To address this issue, several techniques have been
proposed so far to simultaneously reduce test data volume and test power during
scan testing. In this section, we first give an overview of power-aware TDC solutions
proposed so far. Next, we present one of these solutions based on selective encoding
of scan slices.

7.6.1 Overview of Power-Aware TDC Solutions

As proposed in Wang et al. ( 2006 ), power-aware TDC techniques can be classified
into the three following categories: code-based schemes, linear-decompression-
based schemes, and broadcast-scan-based schemes.

7.6.1.1 Code-Based Schemes

The goal of power-aware code-based TDC is to use data compression codes to en-
code the test cubes of a test set so that both switching activity generated in the scan
chains after on-chip decompression and test data volume can be minimized. In the
approach presented in Chandra and Chakrabarty ( 2001 ), test cubes generated by an
ATPG are encoded using Golomb codes. All don't care bits of the test cubes are
filled with 0 and Golomb coding is used to encode runs of 0's. For example, to
encode the test cube “X0X10XX0XX1”, the Xs are filled with 0 and the Golomb
coding provides the compressed data (codeword) “0111010”. More details about