Patent ID: 9252794
Filing Date: 2016-02-02
CPC Classification: H03K,H03L

Claim Text:
1. An on-chip frequency calibration apparatus, comprising: a ring oscillator configured to generate a clock signal variable in frequency; a trimmable resistor coupled to the ring oscillator; a frequency detector configured to detect the frequency of the clock signal generated from the ring oscillator in real-time, wherein the frequency detector includes a frequency divider component that is configured to divide the frequency of the clock signal generated from the ring oscillator by a predetermined number to derive an output signal having a pulse duration that is equal to at least one period of the clock signal generated from the ring oscillator, a capacitor, a capacitor charging current source, and a capacitor charge transistor that is configured to direct a charging current generated from the capacitor charging current source to the capacitor as a function of the output signal generated from the frequency divider component; and a resistor trimming unit configured to trim the trimmable resistor to have an increased resistance in response to determining that the frequency detected by the frequency detector is less than a target ring oscillator frequency threshold.