| 摘要 |
PROBLEM TO BE SOLVED: To test the connection of a clock and all circuits in a CDR circuit at a high speed, in a loop back test of a two-way communication circuit having the CDR circuit. SOLUTION: This communication equipment has a clock selection circuit that receives a multi-phase clock for CDR from a PLL (Phase Locked Loop) to the CDR circuit as an input, and selects and outputs one of the multi-phase clock signals for CDR based on a clock selection signal. At the loop back test time, a clock signal selected by the clock selection circuit is used as a transmission clock, the transmission data is turned up by an input-output terminal and is input into a receiving circuit, data from the receiving circuit is input into the CDR circuit, and a comparing circuit compares reproduced data from the CDR circuit with expected value data, thereby performing the test. By varying the phase of the transmission clock with the clock selection circuit, delay time (= tTx + tRx) of the sum of transmission circuit delay time (tTx) and receiving circuit delay time (tRx) can be varied. COPYRIGHT: (C)2007,JPO&INPIT
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