SU949799A1 - Code to harmonic signal converter - Google Patents

Description

(54) HARMONIC SIGNAL CODE-FREQUENCY CONVERTER

The invention is intended for use in radio installations as a programmable highly stable generator.

The known code-frequency converter contains a frequency code register connected to the input of the accumulator, the output of which is connected to the input of a sine calculator, the output of which is connected to the input of the converter. The analogue code of another input is connected to the output of the clock generator and another input of the accumulator, and the output is connected to the input of the low pass filter G13.

The output signal of the described converter contains spurious frequency components due to the imperfect code-analog converter and the limited size of the sine calculator, and the level of the parasitic components is determined by the sine calculator and the code-analog converter, and their location on the frequency axis is determined by the frequency ratio summation of P and the synthesized frequency When synthesizing a signal with frequencies close to the values of PC, where K is an arbitrary integer, the parasitic components can ahodits arbitrarily close to sintaziruemogo frequency signal, and they fall into the passband lowpass filter and pass therethrough without attenuation.

Also known converter code-frequency harmonic signal,

10 containing multiplying block, counter, serially connected frequency code register, accumulator, cyTviMaTOp, sine calculator, code-analog converter, filter

15 low frequencies, serially connected clock generator, frequency divider, random number generator, reference element and AND element, with the first input of the multiplier

The 20 block is connected to the output of the frequency code register, the second input is connected to the output of a random number generator, and the output is connected to the second input of the adder, the counter input

25 is connected to the output of the clock generator, and the input element And, the reset input of the counter is connected to the output of the frequency divider and the second input of the drive, and the output is connected

Claims (2)

30 with the second input of the reference element. the output element And is connected to the second input of the converter code-analogue. The principle of operation of this transformation consists in the computation and subsequent generation of samples of the synthesized signal, which is performed at pseudo-random instants of time C23. The use of a pseudo-random frequency modulation of the sampling clock frequency, reducing the level of discrete parasitic frequency components, leads to the distribution of their energy in a wide frequency range, i.e. to the appearance of noise components, the spectrum of which is sufficient. but a large repetition period of the pseudo-random sequence can be considered continuous, and the signal-to-noise ratio at the output of the converter is determined by the bandwidth of a low-pass filter. The purpose of the invention is to improve signal-to-noise converter. The goal is achieved by the fact that in the code-frequency converter a harmonic signal containing a frequency code register, the output of which is connected to the first input of the multiplication unit, a drive, a sine calculator, the output of which is connected to the first input of the code-analogue converter, the second input of which connected to the output of the element And, the first input of which is connected to the output of the clock generator and the counting input of the counter, the output of which is connected to the first input of the comparison element, during which it is connected to the second input of the element And, The narrow-band filter and the code converter are both input and the input is connected to the output of the frequency code register, and the output is to the second input of the comparison element and the INPUT of the multiplication unit, the output of which is connected to the first input of the accumulator, the output of which is connected to the sine calculator and the second input is to the output of the AND element and the reset input of the counter, and the output of the code-analogue converter is connected to the input of the kosolosny tracking filter. The structured electrical circuit of the code-frequency converter, the harmonic signal is illustrated in the drawing. The converter contains a frequency code register 1, drive 2, sine calculator 3, analog-code converter 4, clock generator 5, code converter b, logic gates And 7, counter 8, reference element 9, digital replicating unit 10, narrowband tracking filter I. Its principle of operation is as follows. Register 1 is intended for recording and storing the code of the synthesized frequency. This code (or its most significant bits) is converted in the code converter b into a code defining the duration of the summation period in accumulator 2. The code converter conversion table is constructed from the selection conditions for each output code value of this clock frequency (summation period in the accumulator at which the maximum difference between the frequency of the synthesized signal and the nearest point of the integer fnPT is given, g is the selected multiplicity (g m and k integers), since it is at these points that the discrete These parasitic components can approach the signal as much as desired. Fulfillment of this condition makes it possible to achieve in the output signal of converter 4 a code-analogue of such an arrangement of parasitic components on the frequency axis, at which they are absent near the useful signal, which makes it possible to efficiently use a narrowband tracking signal. filter for their suppression. The formation of the required summation period in accumulator 2 is carried out by counting the number of oscillation periods of the oscillator specified by the code converter 5 in counter 8, which is reset when the codes at the inputs of the comparison element 9 and the next counting pulse to the input of logic element 7 are equal. In drive 2, the phase of the synthesized oscillation is calculated by summing the instantaneous phase value corresponding to the front of the previous clock pulse with its increment over the interval between clock pulses. The magnitude of the phase increment is calculated in digital replicating unit 10 by the frequency code and the required summation period. In the sine calculator 3, the phase values are converted into an amplitude value and then, in the converter 4, the code analog to an analog signal, which is filtered by a narrowband tracking filter made, for example, on the basis of a PLL system. The use of adaptive signal processing with the choice of the optimal by the criterion of the maximum distance from the useful signal of the parasitic components, the value-clock frequency of the sample calculation and the following filtering improves the signal-to-noise ratio at the output of the converter compared to the prototype, which expands the range of application of such indicators . The code-frequency converter of a harmonic signal containing a frequency code register, the output of which is connected to the first input of the multiplication unit, a drive, sine calculator, the output of which is connected to the first input of the code-analogue converter, the second input of which is connected to the output of the And element, the first input of which is connected to the output of the clock generator and the counting input of the counter, the output of which is connected to the first input of the comparison element, the output of which is connected to the second input of the AND element, characterized in that that, in order to improve the signal-to-noise ratio, a narrow-band filter and a code converter are inputted, the input of which is connected to the output of the frequency code register, and the output to the second input element; comparison and the second input of the copying unit, the output of which is connected to the first input of the accumulator, the output of which is connected to the input of the sine calculator, and the second input to the output of the And element and the reset input of the counter, and the code analogue converter output is connected to the input of the narrowband filter. Sources of information taken into account during the examination 1. Foreign Radio Electronics, 1972, 3, p.60, Fig.4. 2. USSR author's certificate for the number 2 783 € 44/21, cl.