Auto trimming oscillator

Abstract

An auto trimming oscillator includes a Successive Approximation Register (SAR), a frequency detector and an n-bit comparator. The SAR is used to iteratively trim the oscillator output clock frequency based on a difference between a reference clock frequency and the oscillator output clock frequency. The oscillator is trimmed to deliver a clock frequency which is a closest match to the reference clock frequency.

Description

Technical field [0001] This subject matter generally relates to electronic circuits, and more specifically to fine-tuning oscillator circuits. Background technique [0002] Many modern electronic circuits (e.g., microcontrollers) use internal CMOS oscillators to generate clocks. In many applications, low-variation CMOS oscillators are required. Conventional CMOS oscillators are manually fine-tuned by test engineers using dedicated external tester resources. Some CMOS oscillators use a resistance-capacitance (RC) structure. [0003] Figure 1A shows a conventional RC oscillator with Schmitt trigger. The RC oscillator 100 includes a capacitor 102 (C), a Schmitt trigger 104 (11), and a resistor 106 (R). The output clock 108 has a frequency directly proportional to the RC product. A typical integrated polysilicon resistor can provide a relative frequency change of about + / -25%, and a typical integrated CMOS capacitor can provide a relative frequency change of about + / -15%. In this...

AI Technical Summary

Problems solved by technology

Even with other RC oscillator topologies (e.g. with controlled currents to charge and discharge internal capacitors, etc.), it is not easy to find a solution where the frequency does not directly depend on the RC product

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