s in 100 ns increments. An analog circuit provides an additional fine delay of 0 to 100 ns. A 5 MHz reference clock drives a phase-locked loop to produce a stable 500 MHz clock. It is this fast clock that is gated by the (fine-delayed) start event and determines the main quantization error. The fast clock is divided down to 10 MHz and fed to main counter. The instrument quantization error depends primarily on the 500 MHz clock (2 ns steps), but other errors also enter; the instrument is specified to have 2.2 ns of jitter. The recycle time is 575 ns. Just as a TDC may use interpolation to get finer than one clock period resolution, a delay generator may use similar techniques. The Hewlett-Packard 5359A High Resolution Time Synthesizer provides delays of 0 to 160 ms, has an accuracy of 1 ns, and achieves a typical jitter of 100 ps. The design uses a triggered phase-locked oscillator that runs at 200 MHz. Interpolation is done with a ramp, an 8-bit digital-to-analog converter, and a comparator. The resolution is about 45 ps. When the start pulse is received, then counts down and outputs a stop pulse. For low jitter the synchronous counter has to feed a zero flag from the most significant bit down to the least significant bit and then combine it with the output from the Johnson counter. A digital-to-analog converter (DAC) could be used to achieve sub-cycle resolution, but it is easier to either use vernier Johnson counters or traveling-wave Johnson counters. The delay generator can be used for pulse-width modulation, e.g. to drive a MOSFET to load a Pockels cell within 8 ns with a specific charge. The output of a delay generator can gate a digital-to-analog converter and so pulses of a variable height can be generated. This allows matching to low levels needed by analog electronics, higher levels for ECL and even higher levels for TTL. If a series of DACs is gated in sequence, variable pulse shapes can be generated to account for any transfer function. See also Sampling frequency Multivibrator LIDAR Time-of-flight References External links http://www.freepatentsonline.com/8324952.html traveling wave CMOS traveling wave nFET cascode http://www.febo.com/pages/hp5370b/ http://www.g8wrb.org/useful-stuff/time/HP-5370B/ http://ilrs.gsfc.nasa.gov/docs/timing/artyukh_time_interval_counter.pdf http://ilrs.gsfc.nasa.gov/docs/time_interval_measurements.pdf http://tycho.usno.navy.mil/ptti/1994/Vol%2026_22.pdf http://www.acam.de/fileadmin/Download/pdf/English/AN002_e.pdf Università degli studi Roma Tre, Scuola Dottorale in Scienze Matematiche e Fisiche http://www.ti.com/lit/ds/symlink/tdc7200.pdf Digital circuits Digital signal processing Measuring instruments Radio electronics Signal processing Time