System for controlling the amplitude of an oscillator

• US 6,483,391 B1
• Filed: 03/30/2001
• Issued: 11/19/2002
• Est. Priority Date: 03/30/2001
• Status: Expired due to Term

• Current Assignee: Skyworks Solutions Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Molnar, Alyosha C., Magoon, Rahul, Zachan, Jeff
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US09/823,285
• Time in Patent Office: 599 Days
• Field of Search: 331/109, 331/175, 331/179, 331/182, 331/183, 331/185, 331/186
• US Class Current: 331/183
• CPC Class Codes: H03L 5/00 Automatic control of voltage, current, or power
• CPC Class Codes: H03L 7/087 using at least two phase detectors or a frequency and phase detector in the loop
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/113 using frequency discriminator

Abstract

Systems for controlling the amplitude of the output signal of a controllable oscillator in a frequency synthesizer are provided. One such system provides a circuit having a controllable oscillator and an amplitude control circuit. The controllable oscillator is configured to generate an output signal having a predefined frequency and a predefined amplitude. The controllable oscillator is also configured with a plurality of operational states that are controlled by the amplitude control circuit. Each operational state of the controllable oscillator defines a particular current bias associated with a distinct amplitude of the output signal of the controllable oscillator. The amplitude control circuit receives the output signal of the controllable oscillator and determines the amplitude. When the amplitude of the output signal of the controllable oscillator is less than the predefined amplitude, the amplitude control circuit provides a control signal to the controllable oscillator. The control signal is configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude.

Claims

1. A circuit for maintaining the amplitude of an output signal of a controllable oscillator, comprising:

a controllable oscillator configured to venerate an output signal having a predefined frequency and a predefined amplitude, the controllable oscillator having a plurality of operational states responsive to a plurality of control signals, each of the plurality of operational states corresponding to a particular current bias associated with a distinct amplitude of the output signal of the controllable oscillator; and

an amplitude control circuit in communication with the controllable oscillator, the control circuit configured to determine the amplitude of the output signal of the controllable oscillator and, when the amplitude of the output signal of the controllable oscillator is less than the predefined amplitude, provide the plurality of control signals to the controllable oscillator, the plurality of control signals configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude.

2. The circuit of claim 1, wherein the amplitude control circuit comprises:

a peak detector configured to determine each of the plurality of distinct amplitudes for the output signal corresponding to the plurality of operational states;

a comparator configured to compare each of the plurality of distinct amplitudes for the output signal corresponding to the plurality of operational states to the predefined amplitude; and

logic configured to determine which of the plurality of distinct amplitudes for the output signal corresponding to the plurality of operational states best approximates the predefined amplitude.

3. The circuit of claim 1, wherein the controllable oscillator comprises a plurality of current sources capable of being engaged by the plurality of control signals, the plurality of current sources defining the plurality of operational states of the controllable oscillator.

4. The circuit of claim 1, wherein the logic implements a binary search algorithm to determine the distinct amplitude for the output signal corresponding to the plurality of operational states that best approximates the predefined amplitude.

5. The circuit of claim 1, wherein the amplitude control circuit comprises:

a program counter configured to generate a timing signal based on the predefined frequency, the timing signal having a plurality of clock pulses;

a peak detector configured to generate a first digital word corresponding to the current amplitude of the output signal of the oscillator;

a digital comparator configured to compare the first digital word to a second digital word associated with the predefined amplitude; and

logic configured to receive the timing signal and, in response to each of the plurality of clock pulses, to generate the plurality of control signals based on the comparison of the first digital word to the second digital word.

6. A communication device for use in a communication system, comprising:

a transceiver configured to communicate with the communication system via a communication channel at a particular frequency; and

a frequency synthesizer configured to select the communication channel, the frequency synthesizer comprising;

a controllable oscillator configured to generate an output signal having a predefined frequency corresponding to the particular frequency and a predefined amplitude, the controllable oscillator having a plurality of operational states responsive to a plurality of control signals, each of the plurality of operational states defining a distinct amplitude for the output signal of the controllable oscillator; and

an amplitude control circuit in communication with the controllable oscillator, the amplitude control circuit configured to determine the distinct amplitude for the output signal that best approximates the predefined amplitude and to provide the plurality of control signals, the plurality of control signals configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude.

7. A method for maintaining the amplitude of an output signal of a controllable oscillator at a predefined amplitude level, the controllable oscillator having a plurality of operational states, each of the plurality of operational states corresponding to a particular current bias and defining a distinct amplitude for the output signal of the controllable oscillator, comprising:

determining the amplitude of the output signal of the controllable oscillator;

if the amplitude of the output signal is less than the predefined amplitude level, determining the distinct amplitude for the output signal of the controllable oscillator that best approximates the predefined amplitude level; and

generating a control signal configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level.

8. The method of claim 7, wherein the determining which of the distinct amplitudes for the output signal of the controllable oscillator best approximates the predefined amplitude level involves a binary search algorithm.

9. The method of claim 8, further comprising changing the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level.

10. The method of claim 9, wherein the changing the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level involves configuring a plurality of current sources in a predetermined manner.

11. A method for maintaining the amplitude of an output signal of a controllable oscillator at a predefined amplitude level, the controllable oscillator having a plurality of operational states, each of the plurality of operational states corresponding to a particular current bias and defining a distinct amplitude for the output signal of the controllable oscillator, comprising:

determining the current amplitude of the output signal of the controllable oscillator, the current amplitude corresponding to a current operational state;

comparing the predefined amplitude level to the current amplitude; and

if the current amplitude is less than the predefined amplitude level, based on the comparing the predefined amplitude level to the current amplitude, selecting one of two next operational states, the selected next operational state having a distinct amplitude that better approximates the predefined amplitude level.

12. The method of claim 11, further comprising generating a control signal configured to change the controllable oscillator to the selected next operational state.

13. The method of claim 12, further comprising changing the controllable oscillator to the selected next operational state.

14. The method of claim 13, wherein the changing the controllable oscillator to the selected next operational state involves configuring a plurality of current sources in a predetermined manner.

15. The method of claim 13, further comprising repeating the determining the current amplitude of the output signal of the controllable oscillator, the comparing the predefined amplitude level to the current amplitude, the selecting one of two next operational states, the generating a control signal configured to change the controllable oscillator to the selected next operational state, and the changing the controllable oscillator to the selected next operational state.

16. A system for maintaining the amplitude of an output signal of a controllable oscillator at a predefined amplitude level, the controllable oscillator having a plurality of operational states, each of the plurality of operational states corresponding to a particular current bias and defining a distinct amplitude for the output signal of the controllable oscillator, the method comprising:

means for determining the amplitude of the output signal of the controllable oscillator;

means for determining, when the amplitude of the output signal is less than the predefined amplitude level, the distinct amplitude for the output signal of the controllable oscillator that best approximates the predefined amplitude level; and

means for generating a control signal configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level.

17. The system of claim 16, wherein the means for determining the distinct amplitude for the output signal of the controllable oscillator that best approximates the predefined amplitude level involves a binary search algorithm.

18. The system of claim 17, further comprising means for changing the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level.

19. The method of claim 18, wherein the means for changing the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level comprises a plurality of current sources configured in a predetermined manner.

20. A system for maintaining the amplitude of an output signal of a controllable oscillator at a predefined amplitude level, the controllable oscillator having a plurality of operational states, each of the plurality of operational states corresponding to a particular current bias and defining a distinct amplitude for the output signal of the controllable oscillator, comprising:

means for determining the current amplitude of the output signal of the controllable oscillator, the current amplitude corresponding to a current operational state;

means for comparing the predefined amplitude level to the current amplitude; and

means for selecting, when the current amplitude is less than the predefined amplitude level, one of two next operational states based on the comparing the predefined amplitude level to the current amplitude, the selected next operational state having a distinct amplitude which better approximates the predefined amplitude level.

21. The system of claim 20, further comprising means for generating a control signal configured to change the controllable oscillator to the selected next operational state.

22. The system of claim 21, further comprising means for changing the controllable oscillator to the selected next operational state.

23. The system of claim 22, wherein the means for changing the controllable oscillator to the selected next operational state comprises a plurality of current sources configured in a predetermined manner.

24. The system of claim 23, further configured to repeat the determining the current amplitude of the output signal of the controllable oscillator, the comparing the predefined amplitude level to the current amplitude, the selecting one of two next operational states, the generating a control signal configured to change the controllable oscillator to the selected next operational state, and the changing the controllable oscillator to the selected next operational state.

25. A computer readable medium for maintaining the amplitude of an output signal of a controllable oscillator at a predefined amplitude level, the controllable oscillator having a plurality of operational states, each of the plurality of operational states corresponding to a particular current bias and defining a distinct amplitude for the output signal of the controllable oscillator, the computer readable medium comprising logic configured to determine the amplitude of the output signal of the controllable oscillator, to determine, when the amplitude of the output signal is less than the predefined amplitude level, the distinct amplitude for the output signal of the controllable oscillator that best approximates the predefined amplitude level, and to generate a control signal configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level.

26. The computer readable medium of claim 25, wherein the logic for determining the distinct amplitude for the output signal of the controllable oscillator that best approximates the predefined amplitude level involves a binary search algorithm.

27. The computer readable medium of claim 26, wherein the logic is further configured to change the controllable oscillator to the operational state corresponding to the distinct amplitude that best approximates the predefined amplitude level.

28. A computer readable medium for maintaining the amplitude of an output signal of a controllable oscillator at a predefined amplitude level, the controllable oscillator having a plurality of operational states, each of the plurality of operational states corresponding to a particular current bias and defining a distinct amplitude for the output signal of the controllable oscillator, the computer readable medium comprising logic configure to determine the current amplitude of the output signal of the controllable oscillator, the current amplitude corresponding to a current operational state, to compare the predefined amplitude level to the current amplitude, to select, if the current amplitude is less than the predefined amplitude level, one of two next operational states based on the comparing the predefined amplitude level to the current amplitude, the selected next operational state having a distinct amplitude which better approximates the predefined amplitude level.

29. The computer readable medium of claim 28, wherein the logic is further configured to generate a control signal configured to change the controllable oscillator to the selected next operational state.

30. The computer readable medium of claim 29, wherein the logic is further configured to change the controllable oscillator to the selected next operational state.

31. The computer readable medium of claim 30, wherein the logic is further configured to repeat the determining the current amplitude of the output signal of the controllable oscillator, the comparing the predefined amplitude level to the current amplitude, the selecting one of two next operational states, the generating a control signal configured to change the controllable oscillator to the selected next operational state, and the changing the controllable oscillator to the selected next operational state.