SU470923A1 - Frequency synthesizer - Google Patents

Description

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The invention relates to radio engineering and can be used in radio measuring equipment and radio communications.

A known frequency synthesizer comprising an auxiliary oscillator and tunable oscillator included in a ring, a divider with a constant division factor, a divider with a variable division factor, a phase detector and a low-pass filter.

A disadvantage of the known frequency synthesizer is low speed.

In order to improve speed at high short-term frequency stability, in the proposed synthesizer, a discrete phase shifter is inserted between the dividers, the control inputs of which are connected to the corresponding outputs of the additional splitter, the input of which is connected to the output of the auxiliary generator.

The drawing shows a functional diagram of the proposed frequency synthesizer.

The synthesizer contains a tunable oscillator 1 whose frequency is stabilized by a phase locked loop system consisting of a divider 2 with a constant division factor, a discrete phase shifter 3, a divider 4 with a variable division factor, a phase detector 5 and a low-frequency filter 6. The discrete phase change at the output of the phase shifter 3 is carried out

the signals of the frequency divider 7, to which oscillations are supplied from the auxiliary generator 8. Input 9 serves to supply a reference signal to the phase detector 5, and output

10 of reference oscillator 1 is the output of a frequency synthesizer.

The device works as follows. In the absence of the auxiliary generator signal 8, the state of the splitter 7 frequency does not

changes, and the phase of the signal at the output of the phase shifter 3 remains constant. In this case, the frequency synthesizer is a conventional phase locked loop with a frequency divider in the reverse circuit.

connection. The discreteness of setting the frequency of such a synthesizer depends on the frequency of the reference signal at the input 9 of the phase detector 5, and is equal to the product of this frequency fo by the ratio Ni of the frequency divider 2

f f.N ,.

At the outputs of frequency divider 7, signals alternately appear that, acting on phase shifter 3, cause a step change in the phase of the signal at its output. The number of outputs of the divider 7 and the discreteness of the phase change at the phase shifter 3 are chosen in such a way that in one cycle of operation

the divider phase varies linearly in discrete increments ranging from 0 to 2.

With the linear-step phase change, the signal frequency shifts, therefore, the output of the phase detector 5 generates a control voltage, the value of which depends on the frequency offset of the generator 1 on the frequency of the reference signal and the value of the additional frequency shift due to the linear phase change . As a result, the frequency of oscillator 1 in synchronization mode is set equal to the harmonic frequency of the reference signal of the phase detector with a certain offset proportional to the frequency of the auxiliary oscillator 8, which allows changing the output frequency of the synthesizer within the discreteness of setting its frequency, rearranging the auxiliary oscillator 8 in a certain frequency range.

With the linear-step law of phase change, additional side components also appear in the spectrum of the signal at the input of a frequency divider with a variable division factor, but their distance from the fundamental frequency increases in direct proportion to the number of discrete phase increments at the output of the phase shifter 3.

In the case of a sufficiently large number of these increments, the effective suppression of the lateral components of the spectrum is provided by a phase-locked loop system having a low-pass filter at the output of the phase detector 5 with a relatively wide bandwidth. By widening the lowpass filter bandwidth, the speed of the frequency synthesizer increases, the spectrum of the phase fluctuations at the output of the generator 1 for large offsets from the carrier

approaches the spectrum of the reference signal, which leads to an improvement in the short-term frequency stability in a short averaging time.

Subject invention

A frequency synthesizer that contains an auxiliary oscillator and a tunable oscillator included in the ring, a divider with a constant division factor, a divider with a variable division factor, a phase detector and a low-pass filter, characterized in that in order to increase speed with a high short-term

frequency stability, a discrete phase shifter is inserted between the dividers, the control inputs of which are connected to the corresponding outputs of an additional splitter, the input of which is connected to the output of the auxiliary generator.

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