Test period generator for automatic test equipment

Abstract

A timing subsystem 10 including several test period generators for supplying a variety of timing signals to a device under test. Major, minor, and free-run period generators each supply various timing signals to a multiplexer 18, which selectively connects the timing signals to timing generators 20. A central processing unit 28 supplies data to the period generators and timing generators to define their respective timing signals. Timing signals generated by the major period generator 12 define the overall testing rate. The minor period generator 14 generates multiple timing signals within the periods of the major clock signals to permit higher clock rates. Timing signals that are independent of the major clock periods are generated by the free-run period generator 16. An external synchronizer circuit 26 provides a feedback loop from the device under test 22 to the major period generator. A reference driver trigger delay circuit 27 provides means for calibrating the timing generators. Each of the three period generators includes two interconnected timing interval generators 30 and 40 that alternately generate overlapping timing signals. Each timing interval generator includes a stop-restart oscillator 32, a counter 34, and a delay-line vernier 36. Upon the receipt of a start signal, the oscillator stops and restarts to align its clock pulses to the start signal. The oscillator output clocks the counter, which supplies a signal to the vernier when a preselected number is reached. The vernier delays the counter signal by a preselected delay and issues a signal that designates the end of the period.