A 0.076mm2 3.5GHz spread-spectrum clock generator with memoryless Newton-Raphson modulation profile in 0.13μm CMOS

A spread-spectrum clock generator (SSCG) is a cost-effective solution to reduce EMI, which has become a serious problem in high-speed systems. In applications such as serial links, display drivers and consumer electronics, SSCG is essential or strongly recommended. Control options such as frequency deviation (δ) and modulation frequency (fm) help to satisfy these demands. Furthermore, efficient modulation-profile generation is critical for achieving further EMI reduction and lowering fabrication cost. PLL-based SSCGs are reported in [1–3]. The ΔΣ modulator (ΔΣM) controls the division ratio [1,2] and the phase information of phase detector (PD) [3] to generate a spread-spectrum clock. The self-referenced clock generator uses a capacitor array to generate a spread-spectrum clock [7]. However, they do not have a way to control δ and fm. Dual-loop direct VCO modulation [4] and digital period synthesizer with delay-line [5] are able to control δ and fm. However, [4] requires an additional VCO, which increases the power consumption by 2×, and [5] suffers from a large deterministic jitter through the delay-line and logic circuits. A triangular profile is commonly used in many SSCGs [1,3,4]. Though the implementation of a triangular profile is very simple, its performance is poor. The chaotic PAM modulation in [2] requires complex analog circuits. Recently, a piecewise-linear profile with SRAM was presented in [5]. However, the additional memory consumes a large amount of power and occupies a large area. This paper presents a frequency-locked loop (FLL) based SSCG with frequency-to-voltage converter (FVC) [6], that saves area and provides multiple δ with low bandwidth variation. A memoryless Newton-Raphson modulation profile with multiple fm is also described.