Gct Semiconductor, Inc.

Youngho Ahn

Kyeongho Lee

Joonbae Park

Jeong-Woo Lee

Yido Koo

Eunseok Song

A sigma-delta based phase lock loop device is provided that includes a phase frequency detector (PFD), a charge pump and a voltage controlled oscillator. The PFD to receive a reference signal and a feedback signal and to output signals based on a comparison of the reference signal and the feedback signal. The charge pump to output a charge based on the output signals from the PFD. The charge pump including a first current source to apply a fixed amount of current and a second current source to apply a variable amount of current. The voltage controlled oscillator to output a clock signal based on the received charge from the charge pump.

Sigma-delta based phase lock loop

A system and method for improving the signal-to-noise ratio of a frequency generator suppresses phase noise and noise generated from mismatches in the internal generator circuits. This is accomplished using a modulation scheme which shifts spurious noise signals outside the loop bandwidth of the generator. When shifted in this manner, the noise signals maybe removed entirely or to any desired degree using, for example, a filter located along the signal path of the generator. In one embodiment, a Sigma-Delta modulator controls the value of a pulse-swallow frequency divider situated along a feedback path of a phase-locked loop to achieve a desired level of noise suppression. In another embodiment, a reference signal input into a phase-locked loop is modulated to effect noise suppression. In another embodiment, the foregoing forms of modulation are combined to accomplish the desired frequency shift. Through these modulation techniques, the signal-to-noise ratio of the frequency generator may be substantially improved while simultaneously achieving faster lock times.

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Seoul, South Korea

Youngho Ahn