The design of a wide bandwidth time marker generator.

Abstract

The Time Marker Generator (TMG) is an important instrument that is used to calibrate the time base of an oscilloscope. If a direct digital frequency synthesizer is used to generate the necessary waveforms, there is serious distortion in the generated square wave when the ratio of the sampling frequency to the output frequency is non-integer. In addition, the look-up table (LUT) in the direct digital waveform synthesizer needs a large storage capacity to generate a narrow triangular wave at a low output frequency. This paper proposes a design that will generate the time marker whose samples are synthesized by real-time calculation instead of storing them in a LUT. We also propose an M waveform data synthesizer with a parallel structure (M-WDSPS) to reduce the operating clock frequency of the field programmable gate array (FPGA). We built a 4-WDSPS TMG based on this design and reduced the required clock frequency from 1 GHz to 250 MHz, thus making the implementation possible in an FPGA. Our proposed TMG design can provide square wave, pulse wave, narrow triangular wave, and linear triangular wave with different amplitudes in two operating modes: normal mode and highlight mode. The TMG we constructed can provide the time marker with an output frequency range from 10 mHz to 111 MHz, a rising/falling edge time lower than 1 ns, regardless of whether the output frequency is low or high, and a frequency stability lower than 0.1 ppm.