Yu.A. Bryukhanov - Dr. Sc. (Eng.), Professor, Head of Department of Electronic Systems dynamics, P.G. Demidov Yaroslavl State University E-mail: bruhanov@uniyar.ac.ru Yu.A. Lukashevich - Leading Electronic Engineer, Department of Electronic Systems dynamics, P.G. Demidov Yaroslavl State University E-mail: dcslab@uniyar.ac.ru

Analog-to-digital conversion is conjugated with time sampling and amplitude quantization. Paper is devoted to analysis of influence of sampling and quantization processes on characteristics of radio-receiving device with digital signal processing. This influence is specified by errors of quantizer and overflow, arising from nonlinearity of quantizer characteristic and appearing of new frequencies from sampling. The objective of the paper - analysis of influence of analog-to-digital conversion with arbitrary number of bits for numbers - represen-tation on blocking of useful signal and intermodulation in radio-receiving devices. We use nonlinear quantization model which lets examine processes with arbitrary value of bits R for numbers - representation and also take into account overflow effects. It is necessary to know spectrum of output signal from analog-to-digital conversion (A/D) for analysis of nonlinear phenomena. It is computed with help of classical and modernized discrete Fourier transforms. Calculations show that in case of amplitudes of useful and disturbance signals A1 = 0,5; A2  [0,2; 1] correspondingly values of useful signal blocking coefficient are closed to normative values (0,3 − 0,5) and in case of R ≥ 4 these valued mainly determined by overflow effects which in turn depend on level of disturbance signal. Second order intermodulation coefficient is calculated with useful signal amplitude A = 0,5 and disturbance signals A1 = A2  [0,5; 1]. Its value does not exceed 0,164 in case of R ≥ 4. It is mostly determined by overflow effects which in turn depend on level of radio disturbances. It is shown that in case of sampling second order intermodulation product could be appeared as combination of disturbance frequency in neighboring Nyquist zone and sampling frequency. Calculations show that in case of amplitudes of disturbance signals A1 = A2  [0,5; 1] and R ≥ 4 value of third order intermodulation coefficient is less than 0,126 and is determined by overflow effects which in turn depend on level of radio disturbances. It is shown that third order intermodulation product could arise in case of input to A/D only one disturbance with such frequency that its second harmonic component is in neighboring Nyquist zone. Similar phenomena of arising second and third order intermodulation products are observed in case of subsampling of modulated signals.

 

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