UC Irvine

In this thesis, the design procedure of a frequency-domain diffuse optical imaging system on chip is introduced. The objective of this design is to measure some optical properties of tissue. Using those measurement results, one can find out scattering and absorption coefficient of the tissue. These factors are used to compute the concentration of specific materials inside the human body. The proposed system must precisely compare the phase and amplitude difference between transmitted and detected optical signals. The first version of the chip, which was implemented in a 180 nm CMOS process, used a free-running voltage controlled oscillator (VCO) as the reference signal. In this version, a phase detector unit measures the phase difference between the transmitted and detected signal in the analog domain using a novel feedback system with an N-path filter. In addition, the circuit employed a logarithmic amplifier for amplitude detection. A second version of the chip was designed and fabricated using a 65 nm CMOS process. In this version, a number of changes and modifications were done. For better precision of the phase measurement and reducing jitter, a phase-locked loop (PLL) was designed instead of a free-running VCO. In addition, a down-conversion mixer was used for high-frequency noise filtering and ease of dealing with IF frequency in the phase measurement unit. In this version, phase measurement is done in the digital domain in which the time delay between two square wave signals is attained using a time-to-digital converter. In the third version, the system configuration was chosen to be a heterodyned system. After completion of the whole system design, this version will also be fabricated in 65 nm CMOS. The PLL must provide modulation frequencies between 50 MHz to 500 MHz. In this version, a laser driver is added to be on chip. This circuit needs to provide large amounts of current for different kinds of laser diodes. In addition, this version is going to be less area consuming, with the pin count reduced by using serial-to-parallel converters. Some variations in the time resolution and clocking is done in this version, too. This work can show reasonable results for future operations in wearable optic sensing systems based on frequency-domain near-infrared spectroscopy (fd-NIRS).