# Enhanced Linearity in Intracranial Pressure Monitoring System Through Sample Isolation Bridge ROIC
## 4 Measurement Results  
The micrograph of the die for the test chip is depicted in Figure 12. Realized in 0.18 \(\upmu\)m CMOS technology, the suggested ROIC covers a core area of 0.27 mm\({}^{2}\). The printed circuit board (PCB) has been crafted to assess the functionality of the proposed IC, while the test board, along with the measurement setup, is illustrated in Figure 13.  
Figure 11: Main control schematic and timing diagram. Figure 9: Fully dynamic comparator. The performance of the ROIC has been evaluated through experimental methods. Calibration data processing has been conducted using MATLAB (version R2024a, available at [[https://www.mathworks.com](https://www.mathworks.com)]([https://www.mathworks.com](https://www.mathworks.com))). The ROIC's performance is assessed when the output from the sensor is a 10 \(mV_{pp}\) differential sine wave. The equipment employed to assess the differential nonlinearity (DNL) and integral nonlinearity (INL) of the proposed ROIC is illustrated in Figure 14. The observed peak DNL and INL values are \(-\)0.84/+0.53 LSB and \(-\)0.85/+1.4 LSB, respectively. The DNL and INL errors are mainly caused by the random mismatch between the 25.12/F unit capacitors. The fast Fourier transform (FFT) results of the output bitstream from the ROIC, based on 212 samples, are presented in Figure 15. In Figure 15a, the power spectral density (PSD) of the ROIC, measured with a standard SAR ADC, features a signal-to-noise ratio (SNR) of 40.9 dB and a signal-to-noise and distortion ratio (SNDR) of 40.1 dB. Meanwhile, Figure 15b depicts the measured PSD of the ROIC with a sampled-data isolation-based SAR ADC, which achieves an SNR of 54.6 dB and an SNDR of 51.8 dB. Figure 16 illustrates the measured SNDR in relation to varying input amplitudes. The highest recorded SNDR is 51.8 dB, and the dynamic range (DR) is no less than 50 dB. The ROIC power breakdown results, calculated by simulation, are shown in Figure 17. The IA is still the main source of system power consumption, accounting for 94.74%, despite the low-power design technique. The power consumption of the SAR ADC is only 5.26% of Figure 17. The capacitor array and bootstrapped switch power accounts for only 11% of the total Figure 17 due to the power of the MSB sampling segmented capacitor array and hybrid switching procedure. Since more dynamic logic units are used in the SAR logic, it is still the secondary source of power in the system at 39.4%. Although the comparator uses a two-stage dynamic low-power comparator architecture, it is still the main source of power  
Figure 12: Die micrograph of the proposed ROIC. Figure 13: Integrated Circuit Test Environment with Chip Test Boards. Table 2 summarizes and compares the performance metrics of the proposed ROIC design against alternative ROIC configurations documented in recent literature. Despite inherent variations in signal bandwidth specifications and target applications across these systems, this study focuses on ROIC architectures that incorporate distinct structural combinations, carefully selected to represent both conventional and emerging design paradigms. To establish a standardized framework for cross-configuration analysis, we employ two widely recognized figures of merit: \(FoM_{SNR}\) and \(FoM_{SNDR}\). Figure 13.0  
Figure 13.1  
The determined \(FoM_{SNR}\) and \(FoM_{SNDR}\) values were found to be 149.1 dB and 146.3 dB, respectively. As the gain setting for the preamplifier rises, designing a high-resolution circuit poses greater challenges. In reference [40], the reported \(FoM_{SNR}\) values show a close resemblance to those presented in this research. We clarified that the signal-to-noise ratio reported in [40] is derived from the \(FoM_{SNDR}\) and AC measurements. These estimates  
Figure 13.2 Measured SNDR versus input amplitude. Figure 13.3 Power breakdown of the ROIC. pertain to a preamplifier gain of 100 and a conversion time of 200 ms. Furthermore, the \(FoM_{SNDR}\) attained through this study exceeds those of [37; 40; 41; 42].