**4. Experimental research**

For experimental research a prototype of frequency meter was implemented, based on the block diagram shown in Fig 6. This prototype was implement in the FPGA EP3SL150F1152C2N using the development board STRATIX III EP3SL150 and the design software QUARTUS II. In Fig 7. is shown the circuit diagram to the FPGA based frequency measurement prototype used.

For practical frequency measurement, reference frequency was provided by using an Agilent 33250A arbitrary waveform generator and, was set to <sup>7</sup> 1 10 *of* Hz. The hypothetical unknown frequency was provided by Tektronix AFG3101 Arbitrary function generator.

In Fig. 8a) is presented arbitrary selection from the experimental data set a period value associate to the hypothetical unknown frequency used in experimental research. As shown in Fig. 8a) the measured unknown frequency was adjusted on the rate of *Tx*=989.97ns according to in-built equipment frequency counter. Then this unique pulse train frequency was counted by our experimental prototype of frequency meter. The count of pulses from unknown frequency train obtained with the digital counter Q in block diagram of Fig 6 under the condition (30) is show in Fig. 7 b). The measurement time by single experimentation never exceeds 1 s. It is evident from screenshot Fig. 7 b) that our prototype circuit has a higher resolution than Tektronix AFG3101 in-built frequency counter, but it shows the same rate of frequency. The character of coincidences between indications of experimental prototype and Tektronix AFG3101 generator was the same on all experimental data set. It permits us to make the next important practical conclusion.

Fig. 6. Frequency meter block diagram.

Fig. 7. Circuit diagram for FPGA based frequency meter.

experimentation never exceeds 1 s. It is evident from screenshot Fig. 7 b) that our prototype circuit has a higher resolution than Tektronix AFG3101 in-built frequency counter, but it shows the same rate of frequency. The character of coincidences between indications of experimental prototype and Tektronix AFG3101 generator was the same on all experimental

data set. It permits us to make the next important practical conclusion.

Fig. 6. Frequency meter block diagram.

Fig. 7. Circuit diagram for FPGA based frequency meter.

a)

b)

Fig. 8. Sample frequency (formed by arbitrary function generator, a) measurement by prototype circuit (b).

The prototype circuit unfortunately still has multiply sources of noise and uncertainty. But it is a second plan aspect of circuit optimal design in a future work. The main proof of this prototype circuit is the proof of the possibility for a fast frequency measurement without losses of high resolution and rigorous link to actual situation with frequency jitter in a present pulse train.
