Resonant oscillator circuit with reduced startup transients

• US 8,085,103 B2
• Filed: 12/02/2009
• Issued: 12/27/2011
• Est. Priority Date: 08/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Athas, William C.
• Primary Examiner(s): Chang, Joseph
• Assistant Examiner(s): Tan, Richard
• Application Number:
  US12/629,370
• Publication Number:
  US 20110032043A1
• Time in Patent Office: 755 Days
• Field of Search: 331/108.A, 331/117.R, 331/117.FE, 331/167, 331/172, 331/185
• US Class Current: 331/117.R
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: H03B 2200/0094 Measures to ensure starting of oscillations
• CPC Class Codes: H03B 2200/0096 Measures to ensure stopping of oscillations
• CPC Class Codes: H03B 5/06 Modifications of generator to ensure starting of oscillations
• CPC Class Codes: H03B 5/1212 the amplifier comprising a pair of transistors, wherein an output terminal of each being connected to an input terminal of the other, e.g. a cross coupled pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors

Abstract

Some embodiments of the present invention provide a system that implements a resonant oscillator circuit. This resonant oscillator circuit includes: a first inductor, a second inductor, a first capacitance, and a second capacitance, wherein the first and second inductors are configured to operate with the first and second capacitances to produce resonant oscillations which appear at a first phase output and a second phase output. The system also includes a startup circuit which is configured to start the resonant oscillator circuit in a state where: the first phase output is at a peak voltage; the second phase output is at a base voltage; and currents through the first and second inductors are substantially zero. By starting the resonant oscillator circuit in this state, the oscillations commence without a significant startup transient.

Claims

1. A resonant oscillator circuit, comprising:

a first inductor;

a second inductor;

a first capacitance;

a second capacitance;

wherein the first and second inductors are configured to operate with the first and second capacitances to produce resonant oscillations which appear at a first phase output and a second phase output; and

a startup circuit configured to start the resonant oscillator circuit in a state where the first phase output is at a peak voltage, the second phase output is at a base voltage, and currents through the first and second inductors are substantially zero, so that oscillations commence without a significant startup transient.

2. The resonant oscillator of claim 1,

wherein the first inductor includes a constant potential terminal coupled to an input voltage and a time-varying potential terminal coupled to the first phase output;

wherein the second inductor includes a constant potential terminal coupled to the input voltage and a time-varying potential terminal coupled to the second phase output;

wherein the resonant oscillator circuit also includes a first n-type transistor with a source terminal coupled to a base voltage, a drain terminal coupled to the first phase output, and a gate terminal coupled to the second phase output;

wherein the resonant oscillator circuit additionally includes a second n-type transistor with a source terminal coupled to the base voltage, a drain terminal coupled to the second phase output, and a gate terminal coupled to the first phase output;

wherein the first capacitance includes capacitive components from a load on the first phase output and the gate terminal of the second n-type transistor; and

wherein the second capacitance includes capacitive components from a load on the second phase output and the gate terminal of the first n-type transistor.

3. The resonant oscillator circuit of claim 2, wherein the startup circuit is configured to initially charge the first capacitance so that first phase output is at the peak voltage prior to starting the resonant oscillator circuit.

4. The resonant oscillator circuit of claim 3, wherein the startup circuit is additionally configured to apply the input voltage to the constant-potential terminals of the first and second inductors prior to starting the resonant oscillator circuit.

5. The resonant oscillator circuit of claim 4, further comprising a buck converter configured to apply the input voltage to the constant-potential terminals of the first and second inductors.

6. The resonant oscillator circuit of claim 4, wherein the startup circuit includes a microcontroller, which sequences operations involved in applying the input voltage to the first and second inductors and in initially charging the first capacitance.

7. The resonant oscillator circuit of claim 6, wherein the startup circuit additionally includes a bootstrap circuit configured to produce a pulse voltage which is higher than the output voltage of the microcontroller, wherein the pulse voltage is used to control the initial charging of the first capacitance.

8. The resonant oscillator circuit of claim 1, further comprising an envelope-generation circuit coupled between the input voltage and the resonant oscillator circuit, wherein the envelope-generation circuit is configured to ramp up the input voltage across multiple oscillation periods when the resonant oscillator circuit starts up.

9. The resonant oscillator circuit of claim 2, wherein the startup circuit additionally comprises:

a third n-type transistor with a source terminal coupled to a base voltage, a drain terminal coupled to the first phase output, and a gate terminal coupled to the second phase output; and

a fourth n-type transistor with a source terminal coupled to the base voltage, a drain terminal coupled to the second phase output, and a gate terminal coupled to the first phase output;

wherein the third and fourth n-type transistors have lower threshold voltages than the first and second n-type transistors, which allows oscillations to commence at lower input voltages.

10. A method for starting up a resonant oscillator circuit, wherein the resonant oscillator circuit includes a first inductor, a second inductor, a first capacitance, and a second capacitance, wherein the first and second inductors are configured to operate with the first and second capacitances to produce resonant oscillations which appear at a first phase output and a second phase output, the method comprising:

performing one or more initialization operations so that the resonant oscillator circuit is in an initial state where the first phase output is at a peak voltage, the second phase output is at a base voltage, and currents through the first and second inductors are substantially zero; and

allowing the resonant oscillator circuit to commence oscillations from the initial state without a significant startup transient.

11. The method of claim 10,

wherein the first inductor includes a constant potential terminal coupled to an input voltage and a time-varying potential terminal coupled to the first phase output;

wherein the second inductor includes a constant potential terminal coupled to the input voltage and a time-varying potential terminal coupled to the second phase output;

wherein the resonant oscillator circuit also includes a first n-type transistor with a source terminal coupled to a base voltage, a drain terminal coupled to the first phase output, and a gate terminal coupled to the second phase output;

wherein the resonant oscillator circuit additionally includes a second n-type transistor with a source terminal coupled to the base voltage, a drain terminal coupled to the second phase output, and a gate terminal coupled to the first phase output;

wherein the first capacitance includes capacitive components from a load on the first phase output and the gate terminal of the second n-type transistor; and

wherein the second capacitance includes capacitive components from a load on the second phase output and the gate terminal of the first n-type transistor.

12. The method of claim 10, wherein the one or more initialization operations include initially charging the first capacitance so that first phase output is at the peak voltage prior to commencing the oscillations.

13. The method of claim 11, wherein the one or more initialization operations include applying the input voltage to the constant-potential terminals of the first and second inductors prior to commencing the oscillations.

14. The method of claim 12, wherein the one or more initialization operations are controlled by a microcontroller, which sequences operations involved in applying the input voltage to the first and second inductors and in initially charging the first capacitance.

15. The method of claim 10, wherein the method further comprises ramping up an input voltage for the resonant oscillator circuit across multiple oscillation periods to provide FET inrush protection while commencing oscillations in the resonant oscillator circuit.

16. A resonant oscillator circuit, comprising:

a first inductor with a constant potential terminal coupled to an input voltage and a time-varying potential terminal coupled to a first phase output;

a second inductor with a constant potential terminal coupled to the input voltage and a time-varying potential terminal coupled to a second phase output;

a first n-type transistor with a source terminal coupled to a base voltage, a drain terminal coupled to the first phase output, and a gate terminal coupled to the second phase output;

a second n-type transistor with a source terminal coupled to the base voltage, a drain terminal coupled to the second phase output, and a gate terminal coupled to the first phase output;

a first capacitance, which includes capacitive components from a load on the first phase output and the gate terminal of the second n-type transistor;

a second capacitance, which includes capacitive components from a load on the second phase output and the gate terminal of the first n-type transistor; and

a startup circuit configured to start the resonant oscillator circuit in a state where the first phase output is at a peak voltage, the second phase output is at a base voltage, and currents through the first and second inductors are substantially zero, so that oscillations commence without a significant startup transient.

17. The resonant oscillator circuit of claim 16, wherein the startup circuit is configured to initially charge the first capacitance so that first phase output is at the peak voltage prior to starting the resonant oscillator circuit.

18. The resonant oscillator circuit of claim 17, wherein the startup circuit is additionally configured to apply the input voltage to the constant-potential terminals of the first and second inductors prior to starting the resonant oscillator circuit.

19. The resonant oscillator circuit of claim 18, further comprising a buck converter configured to apply the input voltage to the constant-potential terminals of the first and second inductors.

20. The resonant oscillator circuit of claim 18, wherein the startup circuit includes a microcontroller, which sequences operations involved in applying the input voltage to the first and second inductors and in initially charging the first capacitance.

21. The resonant oscillator circuit of claim 20, wherein the startup circuit additionally includes a bootstrap circuit configured to produce a pulse voltage which is higher than the output voltage of the microcontroller, wherein the pulse voltage is used to control the initial charging of the first capacitance.

22. The resonant oscillator circuit of claim 16, further comprising an envelope-generation circuit coupled between the input voltage and the resonant oscillator circuit, wherein the envelope-generation circuit is configured to ramp up the input voltage across multiple oscillation periods when the resonant oscillator circuit starts up.

23. The resonant oscillator circuit of claim 16, wherein the startup circuit additionally comprises:

a third n-type transistor with a source terminal coupled to a base voltage, a drain terminal coupled to the first phase output, and a gate terminal coupled to the second phase output; and

a fourth n-type transistor with a source terminal coupled to the base voltage, a drain terminal coupled to the second phase output, and a gate terminal coupled to the first phase output;

wherein the third and fourth n-type transistors have lower threshold voltages than the first and second n-type transistors, which allows oscillations to commence at lower input voltages.