High frequency oscillator

1. A frequency oscillator comprising:

a first ring oscillator having N inverters coupled in series, where N is an odd integer equal to three or more;

a first filter coupled between an output node of a first of the inverters and an output line of the frequency oscillator; and

a second filter coupled between an output node of a second of the inverters and the output line of the frequency oscillator, wherein the first and second filters each have a lower cut-off frequency falling between the (N−2)th and the Nth harmonic present at the outputs of the inverters and a higher cut-off frequency falling between the Nth and (N+2)th harmonic present at the outputs of the inverters.

2. The frequency oscillator of claim 1 , wherein the frequency oscillator further comprises a second ring oscillator formed of N inverters coupled in series, wherein at least one line connecting a pair of inverters of the first ring oscillator is positioned to be electro-magnetically coupled to at least one line connecting a pair of inverters of the second ring oscillator.

3. The frequency oscillator of claim 1 , wherein N is equal to 5 or 7.

4. The frequency oscillator of claim 1 , wherein the first filter comprises a first inductor and the second filter comprises a second inductor.

5. The frequency oscillator of claim 1 , wherein an output of at least one of the N inverters is coupled to the input of the next inverter via a further inductor.

6. The frequency oscillator of claim 1 , wherein a frequency signal on the output line has a frequency in the range of 300 GHz to 3 THz.

7. The frequency oscillator of claim 6 , wherein a signal at the output node of the first of the inverters is half or smaller than the frequency of the frequency signal on the output line.

8. The frequency oscillator of claim 6 , wherein each of the inverters comprises a transistor having a gate length of 65 nm or smaller.

9. A method of generating a frequency signal, the method comprising:

generating an oscillating signal using a ring oscillator having N inverters coupled in series, where N is an odd integer equal to three or more, the oscillating signal generated at an output of each of the inverters;

filtering the oscillating signal at the output of at least two of the inverters to extract the Nth harmonic, wherein filtering comprises band-pass filtering around the Nth harmonic, and wherein band-pass filtering includes a lower cut-off frequency falling between the (N−2)th and the Nth harmonic present at the output of at least two of the inverters and a higher cut-off frequency falling between the Nth and (N+2)th harmonic present at the output of at least two of the inverters; and

combining the filtered oscillating signals to generate an output frequency signal.

10. The method of claim 9 , further comprising generating a further oscillating signal using a further ring oscillator having N inverters coupled in series, the further oscillating signal being generated at the output of each of the inverters, wherein at least one line connecting a pair of inverters of the ring oscillator is positioned to be electro-magnetically coupled to at least one line connecting a pair of inverters of the further ring oscillator;

filtering the oscillating signal at the output of at least two of the inverters of the further ring oscillator to extract the Nth harmonic; and

combining the filtered oscillating signals of the further ring oscillator with the filtered oscillating signals of the ring oscillator to generate the output frequency signal.

11. The method of claim 9 , wherein the ring oscillator further comprises a first filter coupled between an output node of a first of the inverters and an output line of the ring oscillator and a second filter coupled between an output node of a second of the inverters and the output line of the ring oscillator.

12. The method of claim 11 , wherein the first filter comprises a first inductor and the second filter comprises a second inductor.

13. The method of claim 9 , wherein N is equal to 5 or 7.

14. The method of claim 9 , wherein the output frequency signal has a frequency in the range of 300 GHz to 3 THz.

15. A terahertz frequency oscillator comprising:

a first transistor having a source, a drain and a gate, the first transistor having a gate length of 65 nm or smaller, the gate of the first transistor being coupled to a drain of an Nth transistor, where N is an odd integer equal to three or more;

a second transistor having a source, a drain and a gate, the second transistor having a gate length of 65 nm or smaller, the gate of the second transistor being coupled to the drain of the first transistor;

a third transistor having a source, a drain and a gate, the third transistor having a gate length of 65 nm or smaller, the gate of the third transistor being coupled to the drain of the second transistor;

a first inductor coupled between the drain of the first transistor and an output line;

a second inductor coupled between the drain of the second transistor and the output line;

a third inductor coupled between the drain of the third transistor and the output line; and

a ground node, wherein the sources of the first, second and third transistors are coupled to the ground node;

wherein the frequency oscillator is configured to carry an output frequency signal having a frequency in the range of 300 GHz to 3 THz at the output line.

16. A terahertz frequency oscillator comprising:

a first transistor having a source, a drain and a gate, the first transistor having a gate length of 65 nm or smaller, the gate of the first transistor being coupled to a drain of an Nth transistor, where N is an odd integer equal to three or more;

a second transistor having a source, a drain and a gate, the second transistor having a gate length of 65 nm or smaller, the gate of the second transistor being coupled to the drain of the first transistor;

a third transistor having a source, a drain and a gate, the third transistor having a gate length of 65 nm or smaller, the gate of the third transistor being coupled to the drain of the second transistor;

a first inductor coupled between the drain of the first transistor and an output line;

a second inductor coupled between the drain of the second transistor and the output line;

a third inductor coupled between the drain of the third transistor and the output line; and

a voltage source coupled to the output line through a fourth inductor;

wherein the frequency oscillator is configured to carry an output frequency signal having a frequency in the range of 300 GHz to 3 THz at the output line.

17. A terahertz frequency oscillator comprising:

a first transistor having a source, a drain and a gate, the first transistor having a gate length of 65 nm or smaller, the gate of the first transistor being coupled to a drain of an Nth transistor, where N is an odd integer equal to three or more;

a second transistor having a source, a drain and a gate, the second transistor having a gate length of 65 nm or smaller, the gate of the second transistor being coupled to the drain of the first transistor;

a third transistor having a source, a drain and a gate, the third transistor having a gate length of 65 nm or smaller, the gate of the third transistor being coupled to the drain of the second transistor;

a first inductor coupled between the drain of the first transistor and an output line;

a second inductor coupled between the drain of the second transistor and the output line;

a third inductor coupled between the drain of the third transistor and the output line;

a fourth inductor coupled between the gate of the first transistor and the drain of the Nth transistor;

a fifth inductor coupled between the gate of the second transistor and the drain of the first transistor; and

a sixth inductor coupled between the gate of the third transistor and the drain of the second transistor;

wherein the frequency oscillator is configured to carry an output frequency signal having a frequency in the range of 300 GHz to 3 THz at the output line.

18. The frequency oscillator of claim 15 , wherein N is equal to 3 so that the third transistor is the Nth transistor.

19. The frequency oscillator of claim 15 , wherein N is equal to 5 or 7.

20. The frequency oscillator of claim 17 , wherein N is equal to 5 or 7.

21. The frequency oscillator of claim 17 , wherein N is equal to 3 so that the third transistor is the Nth transistor.