# Enhanced Linearity in Intracranial Pressure Monitoring System Through Sample Isolation Bridge ROIC
## 1 Introduction  
Intracranial pressure (ICP) monitoring is a critical diagnostic tool for managing traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), hydrocephalus, and other neurological conditions [1]. Current clinical standards define normal adult ICP as 5-15 mmHg, with pediatric ranges slightly lower (3.5-7.5 mmHg) [2, 3]. Accurate ICP measurement is vital for timely intervention, yet existing methodologies face significant trade-offs in precision, invasiveness, and power efficiency [4, 5, 6, 7, 8, 9, 10]. Figure 1 provides a conceptual representation of a deep implant situated within the brain of a TBI patient, enabling precise and long-term monitoring of ICP. State-of-the-art ICP monitoring systems primarily employ three sensor types: strain gauges, fiber optic sensors, and piezoresistive Wheatstone bridge-based sensors [11]. Strain gauges, while cost-effective and widely used, suffer from temperature sensitivity and long-term drift, limiting their reliability in continuous monitoring. Fiber optic sensors offer high accuracy and immunity to electromagnetic interference but require complex fabrication and specialized readout systems, increasing cost and restricting miniaturization (see Table 1). Piezoresistive sensors, configured in Wheatstone bridges, strike a balance between size and precision, making them a preferred choice for implantable systems [12, 13, 14, 15, 16, 17]. Figure 2 depicts a traditional bridge sensor readout system, referred to as the bridge-to-digital converter (BDC). The resistors \(R_{1}\) and \(R_{2}\), shown within the black dashed box, are piezoresistive sensors that are closely matched to two external resistors of 2.5 K\(\Omega\) to minimize offset error and establish a Wheatstone bridge configuration. The resistance of the piezoresistive sensors varies with ICP, and this variation is combined with a matching resistor to generate a differential voltage signal based on the principle of voltage division. This signal is then processed by the instrumentation amplifier (IA) and digitized by the Analog-to-Digital converter (ADC), converting the ICP signal into an observable digital format [18; 19; 20; 21]. To achieve energy-efficient amplification of bridge sensor signals, the IA must exhibit ultra-low noise, offset, and power consumption while maintaining precision [22]. Even with optimized IA and ADC performance, signal distortion persists at their interface due to loading effects and switching noise from ADC sampling networks [23]. Although chopper-stabilized capacitively coupled IAs (CCIAs) improve precision by blocking VCM through input capacitors [24], they introduce output ripple requiring auxiliary ripple reduction circuits, thereby increasing power, area, and design complexity [25]. These limitations have driven recent efforts to co-design IA with successive approximation register (SAR) ADCs, leveraging the latter's inherent low-power advantages while addressing interface-level signal integrity challenges. This work introduces a sample isolation-based readout integrated circuit (ROIC) that combines a cross-connection IA with an innovative SAR ADC architecture to address critical challenges in ICP monitoring systems. The proposed design achieves advancements through \begin{table}
\begin{tabular}{c c c c c c} \hline
**Technology** & **Accuracy** & **Power Consumption** & **Size** & **Complexity** & **Long-Term Stability** \\ \hline Strain Gauges & Moderate & Low & Large & Low & Poor \\ \hline Fiber Optic Sensors & High & Moderate & Medium & High & Excellent \\ \hline Piezoresistive Sensors & High & High & Small & Moderate & Moderate \\ \hline \end{tabular}
\end{table} 
Table 1: Comparative Analysis of ICP Monitoring Technologies. Figure 1: A conceptual perspective on a deep implant situated within the brain of a traumatic brain injury (TBI) patient for precise and prolonged monitoring of intracranial pressure. Figure 2: Conventional bridge-to-digital converter. three interconnected innovations.