Spatially uneven illuminations are the dominant interference of video-based heart rate (HR) screening for cooperated subjects in a telehealth service. In this letter, a remote photoplethysmography (rPPG) method is introduced to stably extract pulsatile signals against uneven facial illuminations based on the multivariate singular spectrum analysis (MSSA). This method first divides the facial skins into multiple patches, where the hue channels resistant to light intensity variations are prepared from selected optimal patches. Considering the spatial correlations of heartbeats, the hue signals are then decomposed using the MSSA to reconstruct pulses. Finally, the HR is determined as the one with the highest ratio of energy around the dominant frequency from the first group of MSSA reconstructed signals. Experimental results demonstrate the effectiveness of the proposed method on the in-house BSIPL-rPPG database and the public COHFACE database, where the correlation coefficients of the estimated HRs achieve 0.95 and 0.98, respectively, outperforming those of the comparison methods.

In this paper, an iterative method is proposed for the optimization of wideband voltage-controlled oscillators (VCOs). The proposed method attempts to improve two significant performance metrics of wideband VCOs, i.e., the nonuniform band distribution and the nonconstant tuning gain KVCO. To address these nonideality issues, we introduce the deviation as a prior knowledge for calibration in each iteration step. The optimal capacitor array weighting plan can be asymptotically approached through multiple iterations. To demonstrate the efficacy of the proposed method, we use it to implement a 1-to-2.4-GHz LC-VCO and achieve a frequency tuning range of 82.4%. The optimized LC-tank involves 64 mixed cells, and each cell contains 2-bit binary-weighted switching capacitors, leading to 256 tuning bands. The LC-VCO with the synthesized tank achieves uniform frequency steps around 5 MHz with the relative error within ±4.4%. Meanwhile, the tuning gain KVCO is around 10 MHz/V with the relative error within ±3.2%. For this LC-VCO design, each iteration step costs about 55.9 s. After seven iterations, we approach the convergent solution where both the relative errors of the frequency steps and the tuning gains satisfy the given specifications.