Low frequency oscillator with ultra-low short circuit current

Patent metadata

Field	Value
Publication number	US-10601408-B2
Application number	US-201815952549-A
Country	US
Kind code	B2
Filing date	Apr 13, 2018
Priority date	Apr 13, 2018
Publication date	Mar 24, 2020
Grant date	Mar 24, 2020

Abstract

In described examples, a sawtooth waveform generator generates a sawtooth waveform having a first rise time. A comb waveform circuit has a power terminal coupled to receive the sawtooth waveform from an output of the sawtooth waveform generator. The comb waveform circuit generates a comb waveform in response to the sawtooth waveform. The comb waveform has a second rise time that is faster than the first rise time.

First claim

What is claimed is:

1. An integrated circuit (IC) comprising:
a sawtooth waveform generator having a generator output, the sawtooth waveform generator configured to generate a sawtooth waveform at the generator output, the sawtooth waveform having a first rise time; and
a comb waveform circuit having a power input and a circuit output, the power input coupled to the generator output, and the comb waveform circuit configured to generate a comb waveform at the circuit output responsive to the sawtooth waveform, the comb waveform having a second rise time faster than the first rise time;
in which the comb waveform circuit includes:
a p-type field effect transistor (PFET) having a first drain, a first source and a first gate, the first source coupled to the power input, and the first drain coupled to the circuit output; and
an n-type field effect transistor (NFET) having a second drain, a second source and a second gate, the second source adapted to be coupled to a supply voltage, and the second drain coupled to the first drain.

2. The IC of claim 1 , wherein the sawtooth waveform generator has a generator input, the comb waveform circuit has a circuit input, the generator output is a first generator output, the IC further comprises a pulse waveform generator having a second generator output, the pulse waveform generator is configured to generate a periodic pulse waveform at the second generator output, the generator input is coupled to the second generator output, and the circuit input is coupled to the second generator output.

3. The IC of claim 2 , wherein the first and second gates are coupled to the circuit input.

4. The IC of claim 2 , wherein one of the first and second gates is coupled to the circuit input, and a different one of the first and second gates is adapted to be coupled to a reference voltage.

5. The IC of claim 1 , wherein the IC further comprises:
a buffer having a buffer input and a buffer output, the buffer input coupled to the circuit output;
a flip-flop having a clock input and a flip-flop output, the clock input coupled to the buffer output, and the flip-flop configured to toggle the flip-flop output responsive to the clock input; and
feedback logic coupled between the flip-flop output and the sawtooth waveform generator.

6. The IC of claim 5 , wherein the buffer includes serially connected inverters, and at least one of the serially connected inverters has a power terminal adapted to be coupled to a current source.

7. An oscillator circuit comprising:
a sawtooth waveform generator having a first generator output, the sawtooth waveform generator configured to generate a sawtooth voltage signal at the first generator output;
a comb waveform generator having a power input and a second generator output, the power input coupled to the first generator output;
a buffer having a buffer input and a buffer output, the buffer input coupled to the second generator output;
a flip-flop having a clock input and a flip-flop output, the clock input coupled to the buffer output, and the flip-flop configured to toggle the flip-flop output responsive to the clock input; and
feedback logic coupled between the flip-flop output and the sawtooth waveform generator.

8. The oscillator circuit of claim 7 , wherein the comb waveform generator includes an inverter having a power terminal, an inverter input and an inverter output, in which the power terminal is coupled to the power input, and the inverter output is coupled to the second generator output.

9. The oscillator circuit of claim 8 , wherein the inverter includes:
a p-type field effect transistor (PFET) having a first drain, a first source and a first gate, the first source coupled to the power terminal, and the first drain coupled to the inverter output; and
an n-type field effect transistor (NFET) having a second drain, a second source and a second gate, the second source adapted to be coupled to a supply voltage, and the second drain coupled to the first drain.

10. The oscillator circuit of claim 9 , wherein the sawtooth waveform generator has a first generator input, the comb waveform generator has a second generator input, the IC further comprises a pulse waveform generator having a third generator output, the pulse waveform generator is configured to generate a periodic pulse waveform at the third generator output, the first generator input is coupled to the third generator output, and the second generator input is coupled to the third generator output.

11. The oscillator circuit of claim 10 , wherein the first and second gates are coupled to the second generator input.

12. The oscillator circuit of claim 10 , wherein one of the first and second gates is coupled to the second generator input, and a different one of the first and second gates is adapted to be coupled to a reference voltage.

13. The oscillator circuit of claim 7 , wherein the buffer includes serially connected inverters.

14. The oscillator circuit of claim 13 , wherein at least one of the serially connected inverters has a power terminal adapted to be coupled to a current source.

15. A method of operating a circuit, the method comprising:
generating a sawtooth waveform having a first rise time responsive to a periodic signal; and
converting the sawtooth waveform to a comb waveform having a second rise time faster than the first rise time, by using the sawtooth waveform to power a buffer circuit using current from the sawtooth waveform;
in which converting the sawtooth waveform to the comb waveform includes receiving the sawtooth waveform at a source of a transistor of the buffer circuit, receiving a reference voltage at a gate of the transistor, and generating the comb waveform at a drain of the transistor.

16. The method of claim 15 , wherein the transistor is a first transistor, the method further comprises receiving a pulse signal at a gate of a second transistor of the buffer circuit, a drain of the second transistor is connected to the drain of the first transistor, and a source of the second transistor is adapted to be coupled to a supply voltage.

Assignees

• Texas Instruments Inc

Inventors

• Chauhan Rajat
• Singhal Vipul Kumar
• Menezes Vinod Joseph
• Mehendale Mahesh Madhukar

Classifications

• H03K4/12

  in which a sawtooth voltage is produced across a capacitor · CPC title

• H03K4/085 Primary

  Protection of sawtooth generators · CPC title

• H03K3/012

  Modifications of generator to improve response time or to decrease power consumption · CPC title

• H03K4/50 Primary

  in which a sawtooth voltage is produced across a capacitor · CPC title

• H03K4/48

  using as active elements semiconductor devices (H03K4/787 - H03K4/84 take precedence) · CPC title