Low voltage operating ring oscillator with almost constant delay time
First Claim
1. A method to achieve a constant delay time of ring oscillators requiring a low operating voltage is comprising the steps of:
- provide a chain ring oscillator comprising a system current source circuit comprising three branches, wherein a first branch comprises a resistance element and a constant voltage circuit comprising an operational amplifier, a bandgap reference circuit, providing input for said operational amplifier, and a transistor and each of the second and third branches comprises a PMOS transistor, an NMOS transistors, a system voltage supply VCC, and n stages, wherein each of the stages of said ring oscillator has a first and a second current source and an inverter circuit and wherein a single-ended output of the inverter circuit of the n-th stage is fed back to the inverter circuit of a first stage;
use said constant voltage circuit to generate in said first branch a first constant current, which is defined by a voltage generated by said constant voltage circuit and said resistance element;
mirror said first constant current to said PMOS transistor of said second branch of said system current source circuit in order to generate a second constant current;
mirror said second constant current from said NMOS transistor of the second branch to said NMOS transistor of said third branch in order to generate a third constant current and to each of said second current sources of each of said stages of said ring oscillator; and
mirror said third constant current from the PMOS transistor of the third branch to each of said first current sources of each of said stages of said ring oscillator.
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Abstract
Methods and circuits for chain ring oscillators having a constant delay time over variations of temperature and variations of semiconductor manufacturing process while requiring low operating voltage only have been disclosed. A system current source includes a constant voltage circuit generating a constant voltage and hence a constant current via a resistance element. Main parts of the constant voltage circuit are an operational amplifier and a bandgap reference circuit. Using a series of current mirrors the constant currents are mirrored to current sources contained in each of n-inverter stages of the chain ring oscillator.
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Citations
13 Claims
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1. A method to achieve a constant delay time of ring oscillators requiring a low operating voltage is comprising the steps of:
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provide a chain ring oscillator comprising a system current source circuit comprising three branches, wherein a first branch comprises a resistance element and a constant voltage circuit comprising an operational amplifier, a bandgap reference circuit, providing input for said operational amplifier, and a transistor and each of the second and third branches comprises a PMOS transistor, an NMOS transistors, a system voltage supply VCC, and n stages, wherein each of the stages of said ring oscillator has a first and a second current source and an inverter circuit and wherein a single-ended output of the inverter circuit of the n-th stage is fed back to the inverter circuit of a first stage; use said constant voltage circuit to generate in said first branch a first constant current, which is defined by a voltage generated by said constant voltage circuit and said resistance element; mirror said first constant current to said PMOS transistor of said second branch of said system current source circuit in order to generate a second constant current; mirror said second constant current from said NMOS transistor of the second branch to said NMOS transistor of said third branch in order to generate a third constant current and to each of said second current sources of each of said stages of said ring oscillator; and mirror said third constant current from the PMOS transistor of the third branch to each of said first current sources of each of said stages of said ring oscillator. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A chain ring oscillator to achieve to achieve a constant delay time requiring a low operating voltage is comprising:
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n identical cascaded stages of inverters, wherein each stage comprises a first and a second stage current source, wherein a current through said first current source is mirrored from a PMOS transistor of a third branch of a system current source, a current through said second current source is mirrored from an NMOS transistor of said third branch of said system current source, and an inverter circuit and wherein a single-ended output of the inverter circuit of the n-th stage is fed back to the inverter circuit of a first stage; a system supply voltage; and said system current source having three branches, generating for each of said two current sources of all said n inverter stages a constant current, wherein said system current source comprises in a first branch a constant voltage circuit comprising an operational amplifier, a bandgap reference circuit, providing input for said operational amplifier, and a transistor, wherein a gate of said transistor is connected to a gate of a PMOS transistor of the second branch and a pate of an NMOS transistor of the second branch is connected to a gate of said NMOS transistor of the third branch. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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Specification