Quantization Noise Cancellation of Fractional-N Frequency Synthesizers Using Pre-distortion Technique

Abstract

This work proposes a novel pre-distortion technique for the quantization noise cancellation of fractional-N frequency synthesizers. The proposed technique utilizes the coordinate rotation digital computer (CORDIC) algorithm to pre-distort the baseband signal of a wireless system with the quantization noise. The pre-distorted signal then modulates the noisy output signal of the fractional-N frequency synthesizer. The transmitter (Tx) modulation quality is thereby improved. In the receiver (Rx) mode, the phase noise of the Rx carrier signal can also be improved by modulation with a pre-distorted sinusoidal signal rather than a baseband signal. Experimental results demonstrate that the novel pre-distortion technique effectively improves the modulation quality of a Tx by an error vector magnitude (EVM) of about 10 % under a 13 Mbps QPSK modulation. The carrier in-band and out-band phase noise of the fractional-N frequency synthesizer is improved by approximately 6 dB and 10 dB, respectively.

Keywords

• Fractional-N frequency synthesizer
• delta-sigma modulation
• quantization noise
• CORDIC
• pre-distortion