RESEARCH OF RELATION OF SAMPLERS FREQUENCY CHARACTERISTICS

The approach to reduce the amplitude noise of a vertical channel of the sampling oscilloscope is presented in this paper. In general, the vertical channel of the sampling oscilloscope consists of a high-frequency sampling circuit and a relatively low-frequency sample transmission path along with a high bit resolution analogto-digital converter. The paper presents a method to improve the sensitivity of the vertical channel of a stroboscopic oscilloscope by extending the conventional channel architecture. The main vertical channel unit of the oscilloscope is a sampling device (sampler), which made of discrete elements and usually implemented using high frequency diodes. The sampler performs a transformation of the sample of the high-frequency signal under test into a low-frequency equivalent signal (otherwise called a balance impulse). In a conventional sampling device, this pulse is quantized once the amplitude is at its highest, thus achieving the best signal-to-noise ratio. The paper analyzes the operating parameters of the sampling device circuit and their influence on the output signal of the sampler. In this approach uses the fastest (15 MHz) high-resolution (18-bit) analog-to-digital converters currently on the market to reduce the amplitude noise of vertical channel based on conventional architecture. Our research has shown that it is possible to obtain an increase in the signal-tonoise ratio of almost 1.3 times.

Hybrid Time-Base Device for Coherent Sampling Oscilloscope

In this paper, a hybrid time-base (HTB) device for the coherent sampling oscilloscope is presented. The HTB device makes it possible to reduce the uncertainty of determining the time position of the sample in the horizontal channel of the sampling oscilloscope. For its functioning, the proposed HTB device requires that the system-under-test, in addition to the test signal, also has a synchronous reference clock – harmonic oscillation. It should be noted that both the test signal and the harmonic reference clock are sampled simultaneously. The harmonic reference clock is connected to one of the oscilloscope channels and a special algorithm processes the clock samples and adjusts the coherent sampling mode. Two techniques of determining the position of the sample on the time axis are combined in the HTB device – the “trigonometric”, when the position is calculated by the arccosine or arcsine formula of the reference clock sampling value, and the interpolation method, according to which the time position of the sample is found by averaging the positions of two adjacent samples, obtained using said “trigonometric” technique. Primary experimental studies have shown that using the HTB device can reduce jitter of the sampling oscilloscope by several times and the drift with constant time distortion components is practically absent in this device.