A 500 MHz time digitizer IC with 15.625 ps resolution

Traditional digitizers provide voltage information about an input signal at fixed time intervals. A time digitizer, on the other hand, provides time information about an input signal at a fixed voltage, typically a zero crossing. This is a useful form of A/D conversion since the information content of many signals is mainly or entirely in their zero crossings. Because a time digitizer samples the zero crossings directly, it can measure the crossing times with much higher effective sample rate than a traditional voltage digitizer. The fast and precise timing of zero crossings enables many high-speed measurements in communications and digital design. This paper describes a monolithic 10b time-digitizer chip in a 25GHz f/sub T/ silicon bipolar process. The chip divides a 16ns period into 1024 intervals or bins, each with a nominal width of 15.625ps. When an input is applied, the chip determines within which of these bins the signal rising-edge crosses zero, and outputs the bin number in binary.<>