Design And Implementation Of The Low Phase Noise And Low Spur In Local Oscillator

With the development of communication technology, the new cellular data technology and wifi technology push the communication test equipment forward higher requirements.Communication test equipments are mainly signal source and spectrum analyzer, signal source and spectrum analyzer both need the qualified local oscillator. This study is frequency synthesizer technology in local oscillator.Local oscillator can provide signal source carrier signal, the carrier signal modulate with the IQ signal(signal generated from the digital signal processing), complete the RF signal source function.It can also provide local oscillator signal for down converted of the spectrum analyzer,local oscillator signal mix with the RF signal, complete the spectrum analyzer function. So the performance of the local oscillator has a significant impact on the upper application, the main performance index of local oscillator are phase noise and spurious and other issues.This thesis mainly research phase noise and more importantly the spurious problem, as follows:Firstly,we introduced phase detector (PD) and voltage-controlled oscillator (VCO), and then make a mathematical analysis of their character.and study the automatic control loop consisted of the two modules, we discusses the characteristics of the loop, including the linear model, frequency response, loop bandwidth. According explored these features, we find the loop filter is very important in PLL.Secondly, we have a detailed discussion of the PLL frequency synthesizer technology, including the principle of the structure, and phase noise, spurious and other properties. By explanation of the fractional PLL frequency synthesizer, we know fractional PLL frequency synthesizer can improve the resolution ratio. But it brought the fractional spurs problem, then we introduce some of the ways to eliminate fractional spurs in previous studies, such as phase compensation and is now widely used to debug DeltaSigma fractional frequency synthesizer. These methods can be improved to some extent in the fractional spurs problem but not ideal.Thirdly,we design and implementation of the local oscillator. We mainly use hmc7031p4e high-resolution frequency synthesis chip provided from HITTITE company to design the low phase noise and low spurious signal of the DC to 6G local oscillator. For fractional spurious problems, by introducing a second reference frequency method, the output frequency can change distribution of the fractional spurs wih second reference frequency.To use second reference frequency at the problem areas of 100MHz reference frequency. Thus, without sacrificing the phase noise,we can solve the problem of fractional spurs. We design a frequency area coverage algorithm to calculate the value of the second reference frequency.For the introduction of the proposed method of the second reference frequency, firstly we use 100MHz as reference frequency to measure the point with problem, and then use the second reference frequency to measure the problem point. According the comparison the two test results,we find that use second reference frequency method eliminates the spurious noise.Finally, And then we make a summary of this thesis and make a future research prospect.