Low-spurious radio frequency signal source

Abstract

The invention provides a low-spurious radio frequency signal source which comprises a DDS (digital direct synthesis) signal source unit, a phase locked frequency conversion unit, a through path, a control unit, a first switch and a second switch, wherein the control unit is used for generating a third control signal; the through path comprises a ground resistor and a third switch; the third switch is used for electrically connecting a signal input end of the through path to a non-grounding end of the ground resistor according to a third control signal when the first switch selects to input a DDS signal to the phase locked frequency conversion unit; when the first switch selects to input the DDS signal to the through path, a circuit between the signal input end of the through path and a signal output end of the through path is connected according to the third control signal. The DDS signal can be input to the ground through the ground resistor, the amplitude of the DDS signal output to an output port through the through path is reduced, spurious signals brought by the through path are reduced, nonharmonic stray of the output signals is reduced, and the spectrum purity of the output signals is improved.

Description

technical field [0001] The invention relates to the technical field of test and measurement, in particular to a low stray radio frequency signal source. Background technique [0002] The RF signal source is a radio frequency signal transmitting device, which can output a signal with stable frequency and amplitude, which can be used to calibrate the spectrum analyzer, simulate and generate various signals required by the user, etc. [0003] The US Patent No. US8044725 "Signal generator with directly-extractable DDS signal source" discloses a radio frequency signal source. Such as figure 1 As shown, the radio frequency signal source 100 includes: a direct digital frequency synthesis (DDS or DDFS, Direct Digital Frequency Synthesis) source unit 101, which is used to perform direct digital frequency synthesis and other processing according to a clock signal to generate a DDS signal; a phase-locked frequency conversion unit 102 , used to perform phase-locking processing and fre...

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Problems solved by technology

[0005] There is a problem in the radio frequency signal source 100 of the prior art: when outputting the output signal in the frequency range of 30-3000MHz, the DDS signal is switched to the phase-locked frequency conversion unit 102 through the switch 104, even if the switching selection of the switch 104 does not switch the DDS signal Input to the direct path 32, because the isolation of the direct path 32 is not good, through space coupling and channel transmission, part of the DDS signal will also be output at the output terminal 34 through the direct path 32, so that the output terminal 34 can output the second signal of 30-3000MHz. In addition to the frequency band signal, there is also a spurious signal brought by a direct path 32

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