PLL filter

Abstract

The invention discloses a PLL filter. A radio frequency intrinsic signal the frequency of which is the same as the frequency of a final radio frequency output signal is connected with an intrinsic drive module in an external connection way to generate two paths of quadrature radio frequency intrinsic signals, then a baseband signal I and Q components connected in the external connection way are performed with frequency up-conversion by a quadrature mixer, a modulation signal modulated to the radio frequency carrier frequency is obtained and directly used as the input of a radio frequency limiter, the other input of the radio frequency limiter is a feedback signal of the final radio frequency output signal, the two paths of input signals are limited by the radio frequency limiter, then thephases of the two paths of input signals are compared according to the frequency of the radio frequency by a radio frequency phase detector, an upper charge signal or a lower discharge signal is generated to control the output of a fully differential charge pump, fully differential control voltage is output to control the oscillation frequency of a differential voltage controlled oscillator via afully differential low-pass filter, and the final radio frequency output signal is output. The PLL filter has the advantages of small nonlinear distortion and little stray emission in the output frequency spectrum.

Description

technical field [0001] The invention relates to an electronic circuit, in particular to a radio frequency PLL filter. Background technique [0002] With a large number of applications of wireless communication systems, wireless communication signals of various frequencies and applications exist in the space at the same time. In order to ensure that each communication system will not interfere with each other, all communication standards have strict restrictions on the signal spectrum emitted by the communication system. For a wireless transmission system, the far-end noise power of the transmitted signal is a harsh indicator. Taking the GSM system as an example, the standard stipulates that the noise energy at a position 20MHZ away from the transmitted signal should be lower than -162dBc / Hz in the transmission spectrum, but for ordinary up-modulation mixers, the noise floor at 20MHZ is already as high as -140~ -150dBc / Hz, it will not be possible to meet the system requirem...

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Problems solved by technology

[0004] The above offset pll filter has the following disadvantages, it needs to provide 2 LO signals, so it is necessary to integrate 2 PLLs in the system to generate LO signals; the IF intermediate frequency needs to be mixed Filtering the post-frequency signal requires two low-pass filters working at the IF intermediate frequency. The linearity requirement of the IF intermediate frequency filter is relatively high. If the linearity cannot meet the index, it will bring nonlinear distortion to the final output signal. Affects EVM (error vector magnitude); due to the presence of two LO signals in the pll loop at the same time, if the circuit and layout design are unreasonable, the cross-coupled feedthrough of the clock will bring unwanted spur emission spurs in the output spectrum

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