A broadband ultra-low phase noise DC frequency modulation reference source circuit

Abstract

The invention provides a direct current frequency modulation reference source circuit of broadband ultra low phase noise. The direct current frequency modulation reference source circuit comprises a digital-to-analog conversion circuit, a data processing and control circuit, a DDS circuit, a band pass filter, a loop filter and an integration frequency synthesis chip. The digital-to-analog conversion circuit controls minimal modulation signals fm to obtain frequency modulation data after conversion of the digital-to-analogue conversion circuit, the frequency modulation data controls the operation with the frequency control words of the DDS circuit through the data processing and control circuit to control the output of the DDS circuit so that modulated signals with ultra low phase noise and ultra low straying, and the modulated signals, after passing through the band pass filter, are sent to the integration frequency synthesis chip to serve as reference signals of a phase-locked loop. By using such a scheme, by use of an analog-to-digital conversion and digital signal processing technologies and DDS and PLL mixing frequency synthesis technologies, direct current frequency modulation of broadband signals by minimal simulation signals can be realized.

Description

technical field [0001] The invention belongs to the technical field of phase noise testing, and in particular relates to a DC frequency-modulating reference source circuit with broadband ultra-low phase noise. Background technique [0002] In the field of phase noise testing, the frequency / phase detection method is one of the main methods for measuring phase noise. It has the characteristics of high measurement sensitivity, wide measurement range, and separable amplitude modulation noise, etc., and is widely used. However, the sensitivity of the measurement is limited by the phase noise of the reference source itself. The reference signal must have an equal frequency according to the signal under test, and the phase noise of the reference signal is better than that of the source under test, so the reference source signal must be a broadband ultra-low phase The synthetic frequency signal of the noise; in addition, in the process of measuring phase noise by the frequency / phase...

AI Technical Summary

Problems solved by technology

[0010] The use of FPGA circuits to achieve fractional frequency division will be limited by the operating frequency of the device and the resolution of the fractional frequency division. It cannot work at a higher frequency and can only work at a lower phase detection frequency. The phase noise of the phase loop frequency synthesizer has an improving effect, so the mentioned prior art cannot optimize the phase noise of the synthesized signal

[0011] Using a single phase-locked loop for frequency synthesis, in the case of a low reference frequency, if the output frequency of the synthesized signal is increased, the frequency division ratio of the loop must be increased, and increasing the frequency division ratio will cause the deterioration of the phase noise of the synthesized signal. Unsuitable reference source for phase noise testing

[0012] If the phase noise of the synthesized signal is further improved on the basis of the existing technology, it is necessary to adopt a multiple phase-locked loop nested structure, which will make the frequency synthesis scheme very complicated and increase the cost

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