Digital clock recovery loop

• US 6,100,765 A
• Filed: 09/16/1999
• Issued: 08/08/2000
• Est. Priority Date: 01/09/1998
• Status: Expired due to Term

• Current Assignee: Round Rock Research LLC
• Original Assignee: Micron Technology, Inc.
• Inventors: O'Toole, James E., Pax, George E.
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US09/397,484
• Time in Patent Office: 327 Days
• Field of Search: 331/1 A, 331/17, 331/25, 331/177 R, 331/78, 327/157, 327/159, 375/376
• US Class Current: 331/1.00A
• CPC Class Codes: H03L 7/0895 Details of the current generators H03L7/0893 takes precedence
• CPC Class Codes: H03L 7/0896 the current generators being controlled by differential up-down pulses
• CPC Class Codes: H03L 7/113 using frequency discriminator
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop

Abstract

A communications system including a clock recovery circuit that extracts a clock signal from incoming digital data, the clock recovery circuit comprising: a voltage controlled oscillator having a control node and an output producing an output wave having a frequency that varies in response to a voltage applied to the control node; charge pump and loop filter circuitry that controls the rate of change of the voltage on the control node of the voltage controlled oscillator; a start-up circuit that performs frequency detection and, in conjunction with the charge pump and loop filter circuitry, adjusts the voltage on the control node of the voltage controlled oscillator; and a state machine that performs phase detection and adjusts the voltage on the control node of the voltage controlled oscillator.

Claims

1. A clock recovery method for extracting a clock signal from an input digital signal in a phase lock loop, the method comprising:

producing, with a voltage controlled oscillator having a control node, an output wave having a frequency that varies in response to a voltage applied to the control node;

controlling, with charge pump and loop filter circuitry, the rate of change of the voltage on the control node of the voltage controlled oscillator;

performing, with start-up circuitry, frequency discrimination and, in conjunction with the charge pump and loop filter circuitry, adjusting the voltage on the control node of the voltage controlled oscillator;

performing phase control and adjusting the voltage on the control node of the voltage controlled oscillator using a state machine;

applying, with bias circuitry, an offset voltage to the voltage controlled oscillator such that, in the absence of any voltage applied to the control node, the frequency of the output wave produced by the voltage controlled oscillator is at least half and not greater than the final frequency of the voltage controlled oscillator when frequency lock is established.

2. A clock recovery method in accordance with claim 1 and further comprising making, with the state machine, finer adjustments to the voltage on the control node of the voltage controlled oscillator than the start-up circuit.

3. A clock recovery method in accordance with claim 1 and further comprising providing an input digital signal that comprises direct spread spectrum data.

4. A clock recovery method in accordance with claim 1 and further comprising implementing the state machine using digital circuitry.

5. A clock recovery method in accordance with claim 1 and further comprising providing an input digital signal that comprises direct spread spectrum data including a plurality of chips, and varying the output of the voltage controlled oscillator until a predetermined number of transitions of the output fit within a time interval of a predetermined number of chips in incoming data.

6. A method of using a phase lock loop to receive an oscillating input signal and produce an output signal, the phase lock loop comprising a plurality of flip-flops which are chained together, the plurality of flip-flops including a first flip-flop having a first output, including a second flip-flop having an input coupled to the first output and having a second output, and including a third flip-flop having an input coupled to the second output, the phase lock loop further comprising a control node, the method comprising:

using the flip-flops to determine time spacing between transitions to perform a frequency comparison of the output signal relative to the input signal;

extracting a clock from an input digital signal; and

performing phase control and adjusting the voltage on the control node of the voltage controlled oscillator.

7. A method in accordance with claim 6 and further comprising making adjustments to the voltage on the control node, using the flip-flops, and wherein performing phase control and adjusting the voltage on the control node comprises making finer adjustments to the voltage on the control node of the voltage controlled oscillator than are made by the flip-flops.

8. A method for receiving an oscillating input signal and producing an output signal using a phase lock loop, the phase lock loop comprising a plurality of flip-flops which are chained together and used to determine time spacing between transitions to perform a frequency comparison of the output signal relative to the input signal, the phase lock loop further comprising a control node, the method comprising:

receiving a digital input signal;

extracting a clock from the digital input signal;

performing phase control and adjusting the voltage on the control node of the voltage controlled oscillator; and

applying an offset voltage to the voltage controlled oscillator such that, in the absence of any voltage applied to the control node, the frequency of the output wave produced by the voltage controlled oscillator is at least half and not greater than the final frequency of the voltage controlled oscillator when frequency lock is established.

9. A communications method for extracting a clock signal from incoming digital data using a clock recovery circuit configured as a phase lock loop, the method comprising:

producing an output wave using a voltage controlled oscillator having a control node and having an output, wherein the output wave has a frequency that varies in response to a voltage applied to the control node;

controlling the rate of change of the voltage on the control node of the voltage controlled oscillator;

performing frequency discrimination and adjusting the voltage on the control node of the voltage controlled oscillator;

performing phase control and adjusting the voltage on the control node of the voltage controlled oscillator;

applying an offset voltage to the voltage controlled oscillator such that, in operation, in the absence of any voltage applied to the control node, the frequency of the output wave produced by the voltage controlled oscillator is at least half and not greater than the final frequency of the voltage controlled oscillator when frequency lock is established.

10. A clock recovery method for extracting a clock signal from an input digital signal in a phase lock loop, the method comprising:

producing, with a voltage controlled oscillator having a control node, an output wave having a frequency that varies in response to a voltage applied to the control node;

controlling, with charge pump and loop filter circuitry, the rate of change of the voltage on the control node of the voltage controlled oscillator;

performing, with start-up circuitry, frequency discrimination and, in conjunction with the charge pump and loop filter circuitry, adjusting the voltage on the control node of the voltage controlled oscillator;

performing phase control and adjusting the voltage on the control node of the voltage controlled oscillator.

11. A communications method for extracting a clock signal from incoming digital data, the method comprising:

a step for producing a wave at an output of a voltage controlled oscillator having a frequency that varies in response to a voltage applied to a control node of the voltage controlled oscillator;

a step for controlling the rate of change of the voltage on the control node of the voltage controlled oscillator;

a step for performing frequency discrimination and for adjusting the voltage on the control node of the voltage controlled oscillator;

a step for performing phase control and for adjusting the voltage on the control node of the voltage controlled oscillator; and

a step for varying the output of the voltage controlled oscillator until a predetermined number of transitions of the output fit within a time interval of an identifiable discrete segment of the incoming data.

12. A communications method in accordance with claim 11 and further comprising a step for applying an offset voltage to the voltage controlled oscillator such that, in operation, in the absence of any voltage applied to the control node, the frequency of the output wave produced by the voltage controlled oscillator is at least half and not greater than the final frequency of the voltage controlled oscillator when frequency lock is established.

13. A communications method in accordance with claim 11 wherein the incoming data is direct spread spectrum data including a plurality of chips.

14. A communications method for extracting a clock signal from incoming digital data, the method comprising:

a step for producing a wave at an output of a voltage controlled oscillator having a frequency that varies in response to a voltage applied to a control node of the voltage controlled oscillator;

a step for controlling the rate of change of the voltage on the control node of the voltage controlled oscillator;

a step for performing frequency discrimination and for adjusting the voltage on the control node of the voltage controlled oscillator;

a step for performing phase control and for adjusting the voltage on the control node of the voltage controlled oscillator;

a step for varying the output of the voltage controlled oscillator until a predetermined number of transitions of the output fit within a time interval of an identifiable discrete segment of the incoming data; and

a step for applying an offset voltage to the voltage controlled oscillator such that, in operation, in the absence of any voltage applied to the control node, the frequency of the output wave produced by the voltage controlled oscillator is at least half and not greater than the final frequency of the voltage controlled oscillator when frequency lock is established.