A Frequency Modulation System with Modulation Depth Compensation

Abstract

The invention discloses a frequency modulating system with the modulation depth compensation function. The frequency modulating system comprises a frequency synthesizer (100) and an analog modulation voltage generating module (200). The frequency synthesizer selects and sets a programmable fractional frequency divider (6) through a channel and generates carrier signals with the corresponding frequency, and then a configurable loop filter (3) is programmed to open a loop; the analog modulation voltage generating module selects and sets the quantized voltage range of a digital-to-analog converter through a channel, the digital-to-analog converter (8) converts digital modulating signals into analog voltage signals, the analog voltage signals are filtered through a low-pass filter (7), then the voltage characteristic is converted into capacity characteristic through a modulation capacitor, and an LC oscillator (4) achieves the frequency modulating function. The modulation depth compensation function is built in, multi-code-rate multi-channel single-modulation-depth communication is achieved, in the modulation process, the loop is opened, the design constraint on the loop bandwidth of the frequency synthesizer is reduced, and carrier jitter and the signal distortion degree are reduced.

Description

technical field [0001] The invention mainly relates to the field of frequency modulation design, in particular to a frequency modulation system structure using a frequency synthesizer for frequency modulation to realize multi-channel and single frequency modulation depth. Background technique [0002] With the development of wireless communication technology, the working frequency range of RF chips continues to expand, and the number of communication channels continues to increase. As a result, how to achieve consistent frequency modulation depth under the same code rate and the same communication protocol has become the main problem in the design of the transceiver system. question. [0003] The traditional frequency modulation function is mainly realized by PLL structure. First, the frequency of the carrier signal is determined according to the channel selection signal, and a high-frequency carrier signal of the corresponding frequency is generated through the PLL; then, ...

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Problems solved by technology

[0007] With the continuous increase of communication channels, the carrier frequency continues to increase, making the effective capacitance C corresponding to the carrier frequency 0 also gradually decreases, but the modulation capacity △C for frequency modulation remains unchanged. According to the formula (1), it can be seen that the modulation depth will become larger and larger, resulting in an increase in the working bandwidth of the digital processing module and an increase in design difficulty.

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