Modulator capable of reducing influence of high-frequency noise in fractional frequency synthesizer, and modulator circuit

Abstract

The invention discloses a modulator capable of reducing the influence of high-frequency noise in a fractional frequency synthesizer, and a modulator circuit. The modulator circuit comprises a gear selection module, a multi-stage cascade modulation module and a notch filtering module, wherein the gear selecting module is used for selecting a decimal intercepting digit and a corresponding notch filtering circuit; the notch filtering module is used for carrying out partial interception before an input decimal value enters the multi-stage cascade modulation module, restoring the value to an original expected value through the notch filtering circuit after processing by the multi-stage cascade modulation module, and reducing the noise spectral density at the high frequency. According to the modulator capable of reducing the influence of the high-frequency noise in the fractional frequency synthesizer, and the modulator circuit, through the modulator and the configurable notch filtering structure of the circuit thereof, the frequency of the output high value can be reduced, and the additional filtering effect on the high-frequency noise is achieved.

Description

technical field [0001] The invention relates to the fields of radio frequency and analog integrated circuits, more specifically, it relates to a modulator capable of reducing the influence of high-frequency noise in a fractional frequency division frequency synthesizer and the modulator circuit. Background technique [0002] Currently, fractional frequency synthesizers all use dual-mode frequency dividers, which inevitably introduce quantization noise and fractional spurs. In order to solve this problem, it is conventional to introduce a Delta-Sigma modulator (DSM) to solve this problem. This module can effectively convert the quantization error in the system into random noise and transfer it to a higher frequency. These high-frequency noises will be suppressed due to the low-pass filtering characteristics of the loop. However, noise shaping using a traditional delta-sigma modulator cannot completely eliminate quantization noise, and the output quantization noise has a larg...

AI Technical Summary

Problems solved by technology

However, noise shaping using a traditional delta-sigma modulator cannot completely eliminate quantization noise, and the output quantization noise has a large amplitude. On the one hand, when the loop bandwidth is large, high-frequency noise cannot be suppressed by the loop filter. It will cause out-of-band noise performance to deteriorate. On the other hand, the output level variation range of the Delta-Sigma modulator is too large, which will cause more significant nonlinear effects in the phase frequency detector (PFD) and charge pump (CP) circuits. , and add frequency synthesizer in-band noise

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