Low voltage annular oscillator with almost constant delay time

Abstract

The present invention relates to a method and circuit requiring only low voltage operation for a chained ring oscillator having a constant delay time across temperature and semiconductor process variations. A system current source includes a constant voltage circuit to generate a constant voltage and thus a constant current through a resistor element. The main parts of the constant voltage circuit are an operational amplifier and a bandgap reference circuit. Using a series of current mirrors, this constant current is mirrored to the current sources contained in the n-stage inverters of each chained ring oscillator.

Description

technical field [0001] FIELD OF THE INVENTION The present invention relates to a ring oscillator circuit, and more particularly, to a ring oscillator circuit having an almost constant delay time even if the operating voltage suddenly drops. Background technique [0002] Ring oscillators are used for a variety of different purposes. Usually the ring oscillator is used as an internally generated clocking source (internally generated clocking source) or in a more complex system: such as a voltage controlled oscillator (voltage controlled oscillator, VCO) or a phase-locked loop (phase locked loop, PLL) as a stage. They are often used to issue an updated command for memory devices such as dynamic random access memory (DRAM). [0003] For applications such as memory circuit design, circuits with constant delay are important. [0004] figure 1 is a known circuit diagram of a chained ring oscillator with five stages of CMOS (complementary metal-oxide-semiconductor) inverters. U...

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Problems solved by technology

[0016] Therefore, if figure 1 As shown, the known ring oscillator can only operate accurately when the voltage difference I1×R1 is much larger than the sum of the threshold voltage |VTHP1|+VTHN1

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