Abstract
A frequency-locked loop (FLL) based spread-spectrum clock generator (SSCG) with a memoryless Newton-Raphson modulation profile is introduced in this paper. The SSCG uses an FLL as a main clock generator. It brings not only an area reduction to the SSCG but also the advantage of having multiple frequency deviations. A double binary-weighted DAC is proposed that modulates the frequency information of the frequency detector using a 1-1-1 MASH <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\Delta \Sigma$</tex></formula> modulator. The Newton-Raphson mathematical algorithm is applied to the proposed profile generator in order to generate the optimized nonlinear profile without needing any memory, resulting in a reduction in the area and the power consumption. It also makes it possible to have multiple modulation frequencies. The SSCG can support 14 frequency deviations of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm 0.5\%$</tex></formula> to 3.5% in steps of 0.5% and three modulation frequencies of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f _{\rm m}$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$2 f _{\rm m}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$3 f _{\rm m}$</tex></formula> . It achieved an EMI reduction of 19.14 dB with a 0.5% down spreading and a 31 kHz modulation frequency, while employing a core area of 0.076 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\hbox{mm}}^{2}$</tex> </formula> in a 0.13- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\hbox{m}}$</tex> </formula> CMOS process and consuming 23.72 mW at 3.5 GHz.
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