Crystal-less oscillator circuit with trimmable analog current control for increased stability

• US 6,798,299 B1
• Filed: 09/19/2001
• Issued: 09/28/2004
• Est. Priority Date: 10/26/2000
• Status: Expired due to Term

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Mar, Monte, Snyder, Warren
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): Luu, An T.
• Application Number:
  US09/957,084
• Time in Patent Office: 1,105 Days
• Field of Search: 331/17, 331/25, 331/43, 331/111, 331/143, 331/158, 331/176
• US Class Current: 331/17
• CPC Class Codes: G06F 1/04 Generating or distributing clock signals or signals derived directly therefrom
• CPC Class Codes: H03B 19/12 using division only
• CPC Class Codes: H03L 2207/10 Indirect frequency synthesis using a frequency multiplier in the phase-locked loop or in the reference signal path
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

A crystal-less oscillator circuit with trimmable current control. In one embodiment, the present invention provides an oscillator circuit comprising a digital to analog converter circuit for generating a current, a band gap reference circuit for generating a voltage, and a relaxation oscillator circuit for creating a frequency based on the current and the voltage. In one embodiment, the digital to analog converter circuit comprises a trimmable current control. In one embodiment, the relaxation oscillator circuit is coupled to a frequency doubler circuit wherein the frequency is passed through the frequency doubler circuit for generating a second frequency. In another embodiment, the present invention provides a phase locked loop circuit comprising a phase detector circuit and the aforementioned oscillator circuit. In another embodiment, the present invention provides a microcontroller comprising a phase locked loop circuit comprising a phase detector circuit and the aforementioned oscillator circuit. The present invention provides an oscillator with stable frequency without the use of a crystal oscillator.

Claims

1. An oscillator circuit comprising:

a digital to analog converter circuit for generating a current and comprising a voltage to current converter circuit for converting a control voltage to a first current and a trimmable current control for generating a second current, wherein said current is a sum of said first current and said second current;

a band gap reference circuit for generating a voltage based on process variations; and

a relaxation oscillator circuit coupled to said digital to analog converter circuit and said band gap reference circuit and for generating a frequency based on said current and said voltage.

2. An oscillator circuit as recited in claim 1 further comprising a frequency doubler circuit coupled to said relaxation oscillator circuit wherein said frequency is passed through said frequency doubler circuit for generating a second frequency.

3. An oscillator circuit as recited in claim 1 wherein said trimmable current control comprises a plurality of trimmable components.

4. An oscillator circuit as recited in claim 1 wherein said trimmable current control is digitally controlled.

5. A phase locked loop circuit comprising:

a phase detector circuit; and

a voltage controlled oscillator circuit comprising;

a digital to analog converter circuit for generating a current and comprising a voltage to current converter circuit for converting a control voltage to a first current and a trimmable current control for generating a second current, wherein said current is a sum of said first current and said second current;

a band gap reference circuit for generating a voltage based on process variations; and

a relaxation oscillator circuit coupled to said digital to analog converter circuit and said band gap reference circuit and for generating a frequency based on said current and said voltage.

6. A phase locked loop circuit as recited in claim 5 wherein said phase detector circuit is for receiving a reference frequency and discriminating the phase difference between said reference frequency and an output frequency and further comprising:

a charge pump circuit coupled to said phase detector circuit and for converting said phase difference into a second current;

a loop filter circuit coupled to said charge pump and said voltage controlled oscillator circuit and for averaging said second current; and

a divider circuit coupled to said voltage controlled oscillator circuit and said phase detector circuit and for generating said output frequency.

7. A phase locked loop circuit as recited in claim 6 further comprising a crystal oscillator circuit coupled to said phase detector circuit and for generating said reference frequency.

8. A phase locked loop circuit as recited in claim 5 further comprising a frequency doubler circuit coupled to said voltage controlled oscillator circuit wherein said frequency is passed through said frequency doubler circuit for generating a second frequency.

9. A phase locked loop circuit as recited in claim 5 wherein said trimmable current control comprises a plurality of trimmable components.

10. A phase locked loop circuit as recited in claim 5 wherein said trimmable current control is digitally controlled.

11. A microcontroller comprising:

a bus;

a processor coupled to said bus;

a memory unit coupled to said bus;

a phase locked loop circuit for generating a frequency and coupled to said bus and comprising;

a phase detector circuit; and

a voltage controlled oscillator circuit comprising;

a digital to analog converter circuit for generating a current and comprising a voltage to current converter circuit for converting a control voltage to a first current and a trimmable current control for generating a second current, wherein said current is a sum of said first current and said second current;

a band gap reference circuit for generating a voltage based on process variations; and

a relaxation oscillator circuit coupled to said digital to analog converter circuit and said band gap reference circuit for generating a frequency based on said current and said voltage.

12. A microcontroller as recited in claim 11 wherein said phase detector circuit is for receiving a reference frequency and discriminating the phase difference between said reference frequency and an output frequency and further comprising:

a charge pump circuit coupled to said phase detector circuit and for converting said phase difference into a second current;

a loop filter circuit coupled to said charge pump and said voltage controlled oscillator circuit and for averaging said second current; and

a divider circuit coupled to said voltage controlled oscillator circuit and said phase detector circuit and for generating said output frequency.

13. A microcontroller as recited in claim 12 further comprising a crystal oscillator circuit coupled to said phase detector circuit and for generating said reference frequency.

14. A microcontroller as recited in claim 11 further comprising a frequency doubler circuit coupled to said voltage controlled oscillator circuit wherein said frequency is passed through said frequency doubler circuit for generating a second frequency.

15. A microcontroller as recited in claim 11 wherein said trimmable current control comprises a plurality of trimmable components.

16. A microcontroller as recited in claim 11 wherein said trimmable current control is digitally controlled.