| 摘要 |
A main driver amplifier generates first differential signals (Vdp/Vdn) based on pattern data (PAT). A replica driver amplifier generates second differential signals (Vcp/Vcn) based on the pattern data (PAT). Two subtractors generate electric potential difference signals (HP=RP−Vep) and (HN=RN−Ven), respectively. Two sample hold circuits sample the electric potential difference signals (HP and HN),and hold them thereafter, respectively. A comparison unit compares a differential amplitude signal (DA=HHP−HHN) with a predetermined threshold value (VOH). A latch circuit latches an output from the comparison unit. Sampling timings of the two sample hold circuits and a latch timing of the latch circuit, can be adjusted independently.
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