RESUMO
This paper presents the design, implementation, and test results of a multichannel time interval and frequency counter developed as a desktop instrument. The counter contains four main functional modules for (1) performing precise measurements, (2) controlling and fast data processing, (3) low-noise power suppling, and (4) supplying a stable reference clock (optional rubidium standard). A fundamental for the counter, the time interval measurement is based on time stamping combined with a period counting and in-period two-stage time interpolation that allows us to achieve wide measurement range (above 1 h), high precision (even better than 4.5 ps), and high measurement speed (up to 91.2 × 106 timestamps/s). The frequency is measured up to 3.0 GHz with the use of the reciprocal method. Wide functionality of the counter includes also the evaluation of frequency stability of clocks and oscillators (Allan deviation) and phase variation (time interval error, maximum time interval error, time deviation). The 8-channel measurement module is based on a field programmable gate array device, while the control unit involves a microcontroller with a high performance ARM-Cortex core. An efficient and user-friendly control of the counter is provided either locally, through the built-in keypad or/and color touch panel, or remotely, with the aid of USB, Ethernet, RS232C, or RS485 interfaces.
RESUMO
The paper describes two time-interval generators based on the phase shifting method. The first one utilizes the digital clock manager units integrated in a field programmable gate array (FPGA) device and has jitter below 65 ps (rms) over the range of 4 ns-50 ms, while the second one utilizes a separate direct digital synthesizer and has jitter below 15 ps (rms) over the range of 10.2 ns-50 ms. The phase shifting method can be used to design new low-cost and high-precision time-interval generators using the popular FPGA technology.
