A Digitally Programmable On-Chip RC-Oscillator in 0.25μm CMOS Logic Process

A 25-MHz Self-Referenced Solid-State Frequency Source Suitable for XO-Replacement

“…In [1], the frequency inaccuracy due to temperature alone was over 2%, while in several recent efforts, including [2] and [3], similar results were obtained. In [3], a 7-MHz compensated ring oscillator was reported to achieve 2.6% total frequency inaccuracy over PVT without frequency trimming.…”

Design of a High Precision, Wide Ranged Analog Clock Generator with Field Programmability Using Floating-Gate Transistors

“…Table 1. Digitally trimmed resistor array RC oscillator inspired from [5] The simulation model of the previous work by [4] is approximated in T-spice under 0.35µm CMOS process. There is seven resistors array and each resistor switches ON/OFF using seven nmos switches.…”

“…The chip area of the simulated model inspired from [5] is estimated. The transistor Effective Area= min poly-silicon width + 2*(min poly to contact spacing) + 2*(min contact size) +2*(min spacing from contact to active area edge).…”

“…Thus, effective area of an nmos switch (for say 25k resistor w=2.7um, l=1um) = 2.7um*1um + 0.54um=3.24sq.um. However, in the paper [5] the impedance of the nmos switches is about 0.15ohm, i.e., (high w/l) nmos was considered (hence larger effective area). In addition, the resistor (25k) will consume approximately 35.75um*35.75um chip area in 0.35um CMOS technology [18].…”

“…However due to large size limitation, opamp offsets and complicated designs respectively, many digitally on-chip trimmed RC oscillator circuit designs [4], [5], [6] have also been developed. These clock generators are temperature insensitive and produce accurate clock which can be digitally trimmed using array of resistors or weighted capacitors.…”