Fast start-up circuit for low power crystal oscillator

Abstract

A method and apparatus for speeding up the start-up process of a crystal oscillator. The energy required for starting oscillations is inserted to the crystal by a stimulus in the form of a time-variant voltage or current pattern, either periodic or aperiodic. The stimulus is stopped after a pre-established period, then the oscillator continues to operate in its normal mode and completes the start-up process significantly faster, compared to a start-up process not comprising the above stimulus.

Claims

1. An electronic circuit, comprising: a fast start-up circuit for purpose of speeding up a start-up of a crystal oscillators; an amplifier comprising a common source amplification stage biased by a controllable current source; a piezoelectric crystal and capacitors connected as a feedback network between the-output and the input of the amplifier in a manner that forms a crystal oscillator; a circuitry that can alter the current flowing in a said amplifier; a start-up pattern consisting of a time-variant stimulus that actively varies the current flowing in a said amplifier and thus inserts energy to the crystal; wherein the spectral content of the time-variant pattern includes a frequency, or plurality of frequencies, close or identical to the natural oscillation frequency of the crystal; a start-up pattern which doesn't require a monitor or detection of a signal strength.

2. The circuit from claim 1, wherein the piezoelectric crystal and the capacitors are connected as a feedback network in a manner that forms a Pierce crystal oscillator.

3. The circuit from claim 1, wherein the piezoelectric crystal and the capacitors are connected as a feedback network in a manner that forms a Colpitts crystal oscillator.

4. The circuit from claim 1, wherein the piezoelectric crystal and the capacitors are connected as a feedback network in a manner that forms a Santos crystal oscillator.

5. The circuit from claim 1, wherein a resistor is connected between the input and the output of the amplifier.

6. The circuit from claim 1, wherein the control of the controllable current source comprises an analogue control.

7. The circuit from claim 1, wherein the control of the controllable current source comprises a digital control.

8. The circuit of claim 1, wherein the time-variant pattern is periodic.

9. An electronic circuit, comprising: a fast start-up circuit for purpose of speeding up a start-up of a crystal oscillator; an inverting amplifier; a piezoelectric crystal and capacitors connected as a feedback network between the output and the input of the amplifier in a manner that forms a crystal oscillator; a circuitry connected to the output of the amplifier that can alter the voltage at the output of a said amplifier; a start-up pattern consisting of a time-variant stimulus that actively varies the voltage at the output of a said amplifier and thus inserts energy to the crystal; wherein the spectral content of the time-variant pattern includes a frequency, or plurality of frequencies, close or identical to the natural oscillation frequency of the crystal; a start-up pattern which doesn't require a monitor or detection of a signal strength; a pair of power supply terminals for connection to the positive and negative voltages of a power source.

10. The circuit from claim 9, wherein the piezoelectric crystal and the capacitors are connected as a feedback network in a manner that forms a Pierce crystal oscillator.

11. The circuit from claim 9, wherein the piezoelectric crystal and the capacitors are connected as a feedback network in a manner that forms a Colpitts crystal oscillator.

12. The circuit from claim 9, wherein the piezoelectric crystal and the capacitors are connected as a feedback network in a manner that forms a Santos crystal oscillator.

13. The circuit from claim 9, wherein a resistor is connected between the input and the output of the amplifier.

14. The circuit from claim 9, wherein the amplifier is realised as a common source stage.

15. The circuit from claim 9, wherein the amplifier is realised as a complementary-MOS (CMOS) logic gate.

16. The circuit from claim 9, wherein the circuitry that can alter the voltage at the output of the said amplifier consists of an n-channel transistor and a p-channel transistor, the drain nodes of both transistors are connected to the output of the amplifier, the source node of the n-channel transistor is connected to the negative supply terminal, the source node of the p-channel transistor is connected to the positive supply terminal, and the gate nodes of the n-channel and the p-channel transistors are connected to a circuitry that can generate a time-variant pattern.

17. The circuit of claim 9, wherein the time-variant pattern is periodic.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

(1) The invention may be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

(2) FIG. 1 is a schematic diagram of the Pierce crystal oscillator, according to prior art.

(3) FIG. 2 is a schematic diagram of the Colpitts crystal oscillator, according to prior art.

(4) FIG. 3 is a schematic diagram of the Santos crystal oscillator, according to prior art.

(5) FIG. 4 is a schematic diagram of a crystal oscillator comprising a start-up shortening technique, according to prior art.

(6) FIG. 5 is a schematic diagram of an amplifier serving in a crystal oscillator comprising a start-up shortening technique, according to prior art.

(7) FIG. 6 is a schematic diagram of a crystal oscillator comprising a start-up shortening technique, according to prior art.

(8) FIG. 7 is a schematic diagram of a crystal oscillator comprising a start-up shortening technique, according to prior art.

(9) FIG. 8 is a schematic diagram of a crystal oscillator comprising a start-up shortening technique, according to prior art.

(10) FIG. 9 is a schematic diagram of a crystal oscillator comprising a start-up shortening technique, according to prior art.

(11) FIG. 10 is a schematic diagram of a crystal oscillator comprising a start-up shortening technique, according to the present invention.

(12) FIG. 11 is an embodiment of the present invention, at which the start-up stimulus is realised as a time-variant current pattern.

(13) FIG. 12 is an embodiment of the present invention, at which the start-up stimulus is realised as a time-variant voltage pattern.

DETAILED DESCRIPTION OF THE INVENTION

(14) The present invention includes a method and apparatus for speeding up the start-up process of a crystal oscillator. The energy required for starting oscillations is inserted to the crystal by a stimulus in the form of a time-variant voltage or current pattern, either periodic or aperiodic. The stimulus is stopped after a pre-established period, then the oscillator continues to operate in its normal mode, swiftly completing the start-up process and proceeding to routine oscillation.

(15) In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

(16) Reference throughout the specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases in one embodiment or in an embodiment in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

(17) For one embodiment of the invention, a crystal oscillator circuit is realised in the Pierce topology (FIG. 1), known to a person skilled in the art.

(18) For another embodiment of the invention, a crystal oscillator circuit is realised in the Colpitts topology (FIG. 2), known to a person skilled in the art.

(19) For another embodiment of the invention, a crystal oscillator circuit is realised in the Santos topology (FIG. 3), known to a person skilled in the art.

(20) For another embodiment of the invention, an amplifier inside the crystal oscillator circuit is realised as a common source amplification stage (1100 in FIG. 11) loaded by a current source (1105 in FIG. 11).

(21) For another embodiment of the invention, an amplifier inside the crystal oscillator comprises a controllable current source (1105 in FIG. 11). Control over the current source may be digital or analogue, and is carried out by a pattern generation circuitry (1106 in FIG. 11).

(22) For another embodiment of the invention, a method is proposed to speed up the start-up time of a crystal oscillator by altering a controllable current source (1105 in FIG. 11) in a certain time-variant pattern.

(23) For another embodiment of the invention, a method is proposed to speed up the start-up time of a crystal oscillator by altering a controllable current source (1105 in FIG. 11) in a periodic pattern.

(24) For another embodiment of the invention, a method is proposed to speed up the start-up time of a crystal oscillator by altering a controllable current source (1105 in FIG. 11) in a periodic pattern that its spectral content includes a frequency, or plurality of frequencies, close or identical to the natural oscillation frequency of the crystal.

(25) For another embodiment of the invention, an amplifier inside the crystal oscillator circuit (1200 in FIG. 12) is realised either as a common source stage or as a complementary-MOS (CMOS) logic gate.

(26) For another embodiment of the invention, a circuitry inside the crystal oscillator comprises an n-channel transistor (1205 in FIG. 12) and a p-channel transistor (1206 in FIG. 12). A pattern generation circuitry (1210 in FIG. 12) sets the gate voltages of the transistors (1205, 1206 in FIG. 12) by means of an appropriate logic circuitry (1207 through 1209 in FIG. 12).

(27) For another embodiment of the invention, a method is proposed to speed up the start-up time of a crystal oscillator by altering a signal or plurality of signals (1208, 1209 in FIG. 12) to open and close a transistor or plurality of transistors (1205, 1206 in FIG. 12) in a certain time-variant pattern.

(28) For another embodiment of the invention, a method is proposed to speed up the start-up time of a crystal oscillator by altering a signal or plurality of signals (1208, 1209 in FIG. 12) to open and close a transistor or plurality of transistors (1205, 1206 in FIG. 12) in a periodic pattern.

(29) For another embodiment of the invention, a method is proposed to speed up the start-up time of a crystal oscillator by altering a signal or plurality of signals (1208, 1209 in FIG. 12) to open and close a transistor or plurality of transistors (1205, 1206 in FIG. 12) in a periodic pattern that its spectral content includes a frequency, or plurality of frequencies, close or identical to the natural oscillation frequency of the crystal.

Advantages of the Invented Embodiments

(30) In the current invention, the start-up process consists of a time-variant stimulus that actively inserts energy to the crystal. It does not consist of noise amplification and energy build up due to positive feedback (regeneration), which is slow. Hence, the current invention achieves faster start-up time compared to regeneration-based techniques.

(31) In the current invention, the spectral content of the stimulus may include a frequency, or plurality of frequencies, close or identical to the natural oscillation frequency of the crystal. Such a stimulus speeds up the start-up process even faster.

(32) In the current invention, the topology of the oscillator and the amplifier remains unchanged during normal operation. Any additional circuitry responsible of start-up boosting, if exists, is neutralised and/or disconnected during normal operation.