Scan speed optimization of input and output paths

1. A scan optimizer system comprising:

multiple parallel scan chains, wherein said scan chains comprise an input path and an output path; and

control logic coupled to said scan chains and comprising a modifier for modifying timing of said input path and said output path;

wherein said control logic is configured to increase a scan frequency by modifying timing offsets of each individual scan chain of said scan chains to affect timing skew between said scan chains to control TDO strobe edges to occur in passing ranges for all of said scan chains.

2. The scan optimizer system of claim 1 , wherein said modifier provides a time delay to at least one of said input path and said output path.

3. The scan optimizer system of claim 2 , wherein said modifier comprises at least one timing vernier in at least one of said input path and said output path.

4. The scan optimizer system of claim 3 comprising timing verniers in said input path configured to control TDI input data edges in each of said scan chains during shift in to position said TDI input data edges near the center of a respective passing range of each of said scan chains.

5. The scan optimizer system of claim 3 comprising timing verniers in said output path configured to control and adjust said TDO strobe edges in each of said scan chains during shift out to position said TDO strobe edges near the center of a respective passing range of each of said scan chains.

6. The scan optimizer system of claim 1 wherein said output path comprises:

an automatic test equipment (ATE) receiver;

a sampling flip-flop coupled to said ATE receiver and controlled by an input from said TDO strobe;

a test processor that receives an output from said sampling flip-flop, wherein said test processor makes a pass/fail decision regarding data sampled by said sampling flip-flop;

a multiplexer that receives said pass/fail decision from said test processor as input, wherein an output from said multiplexer forms a feedback loop comprising a timing vernier that is adjustable to modify timing of said TDO strobe.

7. A computer-implemented method of maximizing scan throughput of multiple parallel scan chains, said method comprising:

controlling TDI input data edges in each of said scan chains during shift in to position said TDI input data edges near the center of a passing range of each of said scan chains;

controlling and adjusting TDO strobe edges during shift out to position said TDO strobe edges near the center of a respective passing range of each of said scan chains; and

increasing a scan frequency by modifying timing offsets of each of said scan chains to affect timing skew between said parallel scan chains to enable said TDO strobe edges for all of said scan chains to occur within said respective passing range.

8. The method of claim 7 wherein said controlling TDI input data edges in each of said scan chains during shift in comprises receiving a test pattern output from a pattern generator into a timing vernier that adjusts timing of said test pattern into an input pad that controls said shift in data.

9. The method of claim 7 wherein said controlling and adjusting TDO strobe edges during shift out comprises:

controlling a sampling flip-flop by an input from said TDO strobe;

making a pass/fail decision regarding data sampled by said sampling flip-flop;

receiving said pass/fail decision at a multiplexer; and

adjusting a timing vernier to modify timing of said TDO strobe according to an output from said multiplexer.

10. A computer-implemented method of maximizing scan throughput of multiple parallel scan chains, said method comprising:

a) choosing a safe shift frequency;

b) determining optimal scan pin timing at said safe frequency, wherein said determining optimal scan pin timing at said safe frequency comprises modifying timing offsets of each of said scan chains to affect timing skew between said scan chains to enable said TDO strobe edges for all of said scan chains to occur within stable regions;

c) determining and applying per-pin timing settings for TDI, TDO, and Mode control pins; and

d) determining a maximum shift frequency associated with said per-pin timing settings.