Physical Unclonable Functions (PUFs) are promising security primitives in recent times. A PUF is a die-specific random function or silicon biometric that is unique for every instance of the die. PUFs derive their randomness from the uncontrolled random variations in the IC manufacturing process which is used to generate cryptographic keys. Researchers have proposed different kinds of PUF in last decade, with varying properties. Quality of PUF is decided by its properties like: uniqueness, reliability, uniformity etc. In this paper we have designed a novel CMOS based RO PUF with improved quality metrics at the cost of additional hardware. The novel PUF is a modified Ring Oscillator PUF (RO-PUF), in which CMOS inverters of RO-PUF are replaced with Feedthrough logic (FTL) inverters. The FTL inverters in RO-PUF improve the security metrics because of its high leakage current. The use of pulse injection circuit (PIC) is responsible to increase challenge-response pairs (CRP's). Then a comparison analysis has been carried out by simulating both the PUF in 90 nm technology. The simulation results shows that the proposed modified FTL PUF provides a uniqueness of 45.24% with a reliability of 91.14%.