Research On Adaptive Phase-locked Technique At 10GHz

The lock-in technique has been widely used in various fields for its superior performance, since it was brought forward. Analog phase-locked loop has advantages such as high-frequency and good spectral characteristics, which digital phase-locked loop does not have, while adaptive lock-in technique this paper presents also overcomes the shortcomings that the instantaneous phase of output signal, that the VCO in traditional analog phase-locked loop provides, appear abnormal changes.This paper studies adaptive technology. Being different from the traditional phase-locked system which uses the reference to compare with voltage control oscillator output signal for phase detection, the method of this study is the voltage controlled oscillator output signal is divided into a certain percentage treatment and then the two phases are detected, all after being amplified. As a part of the signal is processed by high carrier suppression component, a low noise error signal is obtained and then it is input to the RF port of a double balanced diode mixer which is used to be the phase detector, and while, the other part is input to the LO port, after the phase is adjusted to 90° from the phase of the RF signal by the variable phaseshifter. The two signals mix together and become an error signal, of which the voltage accurately reflects the differences between the frequencies the VCO outputs and the locked-in signal. The high frequency portion of the phase error signal outputing by the phase detector is filtered by the loop filter, and we get a voltage which has an approximate linear relationship between the frequency differences. In order to solve the problem that the control voltage does not correspond with the free oscillation, the output signal of the loop filter must plus a DC voltage through an adder, before it becomes practical to control the voltage controlled oscillator. The phase detector is a very good performance diode mixer, so the relative amplitude and phase modulation noise is very low and can be negligible, being relative to noise of the VCO. Noise of the system is mainly from the amplifier, high carrier suppression component and phaseshifter.Based on the theory above, this paper finished design and simulation of phase-locked system, the test of system module, voltage-controlled oscillator, a directional coupler, phase shifters, mixers, adders, loop filter, and the whole lock-in system. The simulation results show that the system is stable, and the phase noise is calculated to achieve that the results are better than that the conventional lock-in technique shows. The preliminary evidence shows the adaptive phase lock technique is feasibility.