BUILT-IN-SELF-TEST CIRCUITRY FOR TESTING A PHASE LOCKED LOOP CIRCUIT

摘要

A built-in-self-test circuit (11) aids in testing a phase locked loop circuit (10). The phased locked loop has a plurality of frequency multipliers. The built-in-self-test circuit (11) includes a frequency divider (24) and a multiplexer (25). The frequency divider (24) has a plurality of divide-by-counters. For each frequency multiplier within the plurality of frequency multipliers there is a corresponding divide-by-counter. A ratio of a multiplier for each frequency multiplier to a divider (24) of its corresponding divide-by-counter is a constant for all frequency multipliers and corresponding divide-by-counters. When a frequency multiplier within the plurality of frequency multipliers is selected, the multiplexer (25) selects its corresponding divide-by-counter to produce a test output clock (14).