SU964984A1 - Digital frequency synthesizer - Google Patents

Description

The invention relates to radio engineering and can be used to form a grid of frequencies in radio transmitting, receiving and radio measuring devices.

A digital frequency synthesizer is known, which contains a series-connected controlled oscillator, a frequency divider with a variable division factor and a frequency-phase detector, as well as a reference oscillator, the first and second stable current generators, and a low-pass filter 1.

However, the known digital frequency synthesizer does not provide a sufficiently high short-term stability of the output frequency.

The closest to the proposed technical solution is a digital frequency synthesizer containing a series-connected controlled oscillator, a variable division frequency divider and a frequency-phase detector, to the other input of which the output of the reference oscillator is connected, as well as the first, second and third stable oscillators current, the outputs of which are combined and through the bottom filter

frequencies are connected to the control input of the controlled oscillator 21.

Such a synthesizer also does not provide a sufficiently high spectral purity of the output signal due to the presence in the output signal spectrum of an interference with a frequency of comparison arising from the non-simultaneous arrival of pulses.

10 to the control inputs of the current generators.

The purpose of the invention is to increase the spectral purity of the output oscillations.

15

The goal is achieved by the fact that in a digital frequency synthesizer, containing a series-connected controlled oscillator, a frequency divider with variable division factor 20 and a frequency-phase detector, the output of the reference oscillator is connected to another input, as well as the first, second and third stable current generators, whose outputs

Claims (2)

25 are combined and are connected via a low-pass filter to the control input of the controlled generator, the first delay element is inserted between the first output of the frequency-phase detector and the input of the first stable current generator, and the output of the reference generator and the input of the second stable current generator are connected in series a pulse shaper, a second delay element, and an OR element, the second input of which is connected to the second output of the frequency-phase detector. The drawing shows the structure of the electrical scheme of the proposed device. The digital frequency synthesizer contains a controlled oscillator 1, a variable division factor 2 (DPCD), a frequency-phase detector: 3, a reference oscillator 4, a new stable current generator 5, the second stable current generator, the third stable current generator low-pass filter ( LPF 8, pulse generator 9, the first delay element 10, the second, the holder element 11, and the element OR 12. The digital frequency synthesizer works as follows. In synchronization mode, the pulses from the output of the pulse generator of pulses 9, the duration of which is selected are not much longer than the value of the dead zone of the frequency-phase detector 3, through the second delay element 11 and the element OR 12 are supplied to the control input of the second stable current generator b, whose current has a negative polarity. Under the action of these pulses, the output frequency of the controlled oscillator 1 periodically decreases. Through DPKD 2, the output frequency of the controlled oscillator 1 is fed to one of the inputs of the frequency-phase detector 3, which leads to the appearance of control pulses from the first output of the frequency-phase detector 3, which through the first delay element 10 enters the input of the first stable current generator 5, the output signal of which compensates for the frequency deviation of the controlled oscillator 1, arising under the action of pulses from the output of the pulse former 9, as well as due to the presence of leakage currents of the low-pass filter elements 8 and stable current generators a, 5 and 6. Choose the current of the third stable current generator 7 equal and opposite in. the magnitude of the leakage current of the elements of the frequency synthesizer; compensation of the current of the leakage is achieved. Due to the nonidentity of the passage of control pulses to the control inputs of the first and second stable current generators 5 and 6 between the output current pulses of these generators, there will be no synchronism, which leads to the appearance of ripples at the input of the controlled generator 1 with the frequency of the reference generator 4. Since the absolute values of the currents of the first and second generators of the stable current 5 and 6 are chosen to be equal, then synchronize the moments of arrival of the pulses to the inputs of the first and second generators of a stable current 5 and b by adjusting irovki velichinEL element, the delay element delays 1.0 or 11 may be mutually offset current pulses acting on the input LPF 8, that leads to znachitelnsmlu reduce spurious components in the spectrum of the output waveform synthesizer while maintaining a high short-term frequency stability. DETAILED DESCRIPTION OF THE INVENTION A digital frequency synthesizer containing a series-connected controlled oscillator, a frequency divider with variable division factor and a frequency-phase detector, to the other input of which the output of the reference oscillator is connected, as well as the first, second and third stable current generators, the outputs of which are combined the low-pass filter is connected to the control input of the controlled oscillator, about t-, characterized in that, in order to increase the spectral purity of the output oscillations, between the first output h The first delay element was inserted into the hundred-phase detector and the input of the first stable current generator, and the pulse generator, the second delay element, and the OR element, the second input of which is connected to the second output h, are inserted between the output of the reference generator and the input of the second stable current generator. astho-phase detector. Sources of information taken into account in the examination 1. Patent CU1A 3714463, file 311-1, 01/30/73. 2. Author's certificate of the USSR according to application 2903815, cl, And 03L 7/18, 26.03.80 (prototype).