Title:

Kind
Code:

A1

Abstract:

A programmable fractional phase-locked loop for generating a 148.50000 MHz high-definition television reference clock and a 148.35164 MHz high-definition reference clock from a 27 MHz crystal is disclosed. To generate the 148.50000 MHz reference clock, the fractional phase-locked loop is multiplied by 11/2, and to generate the 148.35164 MHz reference clock, the fractional phase-locked loop is multiplied by 500/91. Inside the fractional-phase locked loop however, the fraction 11/2 is represented by a denominator that is an integral power of 2, and the fraction 500/91 is represented by a denominator that is an integral multiple of 91.

Inventors:

Arbel, Ygal (Morgan Hill, CA, US)

Application Number:

11/383551

Publication Date:

11/22/2007

Filing Date:

05/16/2006

Export Citation:

Assignee:

METTA TECHNOLOGY, INC. (San Jose, CA, US)

Primary Class:

Other Classes:

327/113, 331/18

International Classes:

View Patent Images:

Related US Applications:

Primary Examiner:

YENKE, BRIAN P

Attorney, Agent or Firm:

Broadcom Limited (Fort Collins, CO, US)

Claims:

What is claimed is:

1. An apparatus comprising: a phase detector for generating a first signal based on the phase difference of a second signal and a third signal; a filter for filtering said first signal; a voltage-controlled oscillator for generating a fourth signal based on said first signal; and a fractional divider for generating said second signal based on said fourth signal, wherein said fractional divider divides said fourth signal by a fraction that has a denominator that is an integral multiple of 91.

2. The apparatus of claim 1 wherein said denominator is 65,520.

3. The apparatus of claim 1 wherein said fraction has a numerator that is an integral multiple of 500.

4. The apparatus of claim 3 wherein said numerator is 360,000.

5. An apparatus comprising: a control input for receiving a control signal; and a fractional divider whose denominator is an integral multiple of 91 when said control signal is in a first state and whose denominator is an integral power of 2 when said control signal is in a second state.

6. The fractional phase-locked loop of claim 5 wherein said denominator is 65536 when said control signal is in said first state and wherein said denominator is 65520 when said control signal is in said second state.

7. The fractional phase-locked loop of claim 5 wherein said numerator is 360,448 when said control signal is in said first state and wherein said denominator is 360,000 when said control signal is in said second state.

8. A television comprising: a reference clock for generator a first signal; a first clock multiplier for generating a second signal by multiplying the frequency of said first signal by 11/2; a second clock multiplier for generating a third signal by multiplying the frequency of said first signal by 500/91; an HD/SD decoder for generating a video signal based on said second signal and said third signal; and a display for displaying said video signal.

1. An apparatus comprising: a phase detector for generating a first signal based on the phase difference of a second signal and a third signal; a filter for filtering said first signal; a voltage-controlled oscillator for generating a fourth signal based on said first signal; and a fractional divider for generating said second signal based on said fourth signal, wherein said fractional divider divides said fourth signal by a fraction that has a denominator that is an integral multiple of 91.

2. The apparatus of claim 1 wherein said denominator is 65,520.

3. The apparatus of claim 1 wherein said fraction has a numerator that is an integral multiple of 500.

4. The apparatus of claim 3 wherein said numerator is 360,000.

5. An apparatus comprising: a control input for receiving a control signal; and a fractional divider whose denominator is an integral multiple of 91 when said control signal is in a first state and whose denominator is an integral power of 2 when said control signal is in a second state.

6. The fractional phase-locked loop of claim 5 wherein said denominator is 65536 when said control signal is in said first state and wherein said denominator is 65520 when said control signal is in said second state.

7. The fractional phase-locked loop of claim 5 wherein said numerator is 360,448 when said control signal is in said first state and wherein said denominator is 360,000 when said control signal is in said second state.

8. A television comprising: a reference clock for generator a first signal; a first clock multiplier for generating a second signal by multiplying the frequency of said first signal by 11/2; a second clock multiplier for generating a third signal by multiplying the frequency of said first signal by 500/91; an HD/SD decoder for generating a video signal based on said second signal and said third signal; and a display for displaying said video signal.

Description:

The present invention relates to information technology in general, and, more particularly, to video decoding.

The decoding and display of standard-definition video signals requires a reference clock with a frequency that is an integral multiple of 27 Mhz and the decoding and display of high-definition video signals requires a reference clock with a frequency of 148.35164 MHz, which is not an integral multiple of 27 MHz. Furthermore, some other high-definition video signals require a reference clock with a frequency of 148.5 MHz, which is also not an integral multiple of 27 MHz. The techniques for generating these three reference clocks simultaneously from the same reference crystal clock source in the prior art all have disadvantages, and, therefore, the need exists for a more elegant solution for doing so.

The present invention provides an apparatus for generating a 148.50000 MHz reference clock and a 148.35164 MHz reference clock from a 27 MHz signal without some of the costs and disadvantages for doing so in the prior art. In accordance with the illustrative embodiment, a crystal clock source provides a 27 MHz signal to a fractional phase-locked loop that multiplies the signal by a mixed fraction N.

To generate the 148.50000 MHz reference clock, the fraction is 11/2, and to generate the 148.35164 MHz reference clock, the fraction is 500/91. Inside the fractional-phase locked loop however, the fraction 11/2 is represented by a fraction with a denominator that is an integral power of 2, and the fraction 500/91 is represented by a fraction with a denominator that is an integral multiple of 91. In accordance with the present invention, a control signal changes the representative denominator between two similar values—the integral power of 2 and the integral multiple of 91—so that one fractional phase-locked loop design will suffice for both denominators.

The illustrative embodiment of the present invention comprises: a phase detector for generating a first signal based on the phase difference of a second signal and a third signal; a filter for filtering said first signal; a voltage-controlled oscillator for generating a fourth signal based on said first signal; and a fractional divider for generating said second signal based on said fourth signal, wherein said fractional divider divides said fourth signal by a fraction that has a denominator that is an integral multiple of 91.

FIG. 1 depicts a block diagram of the salient components of television **100**.

FIG. 2 depicts a block diagram of the salient components of clock multiplier **102**-*i*, wherein i is a member of the set {1, 2}.

FIG. 1 depicts a block diagram of the salient components of television **100**. Television **100** is capable of displaying both high-definition and standard-definition signals as described below. Television **100** comprises: clock source **101**, clock multiplier **102**-**1**, clock multiplier **102**-**2**, HD/SD decoder **103**, and display **104**, interconnected as shown. It will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention in which both high-definition and standard-definition displays are present and simultaneously displaying the same image (although in different definitions).

In accordance with the illustrative embodiment, clock source **101** is a crystal oscillator that generates a 27 MHz clock signal on lead **111**, in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention in which clock source **101** has a different frequency. Furthermore, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that use something other than a crystal for clock source **101**.

In accordance with the illustrative embodiment, clock multiplier **102**-**1** receives:

i. the 27 MHz clock signal from clock source **101** on lead **111**, and

ii. a control signal, which is in a first state, on lead **113**-**1**

and generates a 148.50000 MHz HD reference signal on lead **112**-**1**, as described in detail and in the accompanying figures. It will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention in which the output of clock multiplier **102**-**1** has a different frequency.

In accordance with the illustrative embodiment, clock multiplier **102**-**2** receives:

i. the 27 MHz clock signal from clock source **101** on lead **111**, and

ii. a control signal, which is in a second state, on lead **113**-**2**

and generates a 148.35164 MHz SD reference signal on lead **112**-**2**, as described in detail and in the accompanying figures. It will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention in which the output of clock multiplier **102**-**2** has a different frequency. Although the illustrative embodiment comprises two clock multipliers, it will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that comprise any number of clock multipliers.

In accordance with the illustrative embodiment, HD/SD decoder **103** receives the 148.50000 MHz HD reference signal on lead **112**-**1** and the 148.35164 MHz SD reference signal on lead **112**-**2** and uses them, in well-known fashion, to decode an HD or SD encoded signal, as appropriate, for display on display **104**.

In accordance with the illustrative embodiment, display **104** is a liquid crystal display that displays the image provided by HD/SD decoder **103**. It will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention in which display **104** uses another technology.

FIG. 2 depicts a block diagram of the salient components of clock multiplier **102**-*i*, wherein i is a member of the set {1, 2}. Clock multiplier **102**-*i *receives the 27 MHz clock signal from clock source **101** on lead **111** and outputs either (a) a 148.50000 MHz HD reference signal, or (b) a 148.35164 MHz SD reference signal on lead **112**-*i*, depending on the state of the control signal on lead **113**-*i*. When the control signal on lead **113**-*i *is in the first state, the 148.35164 MHz SD reference signal is output on lead **112**-*i*, and when the control signal on lead **113**-*i *is in the second state, the 148.35164 MHz SD reference signal is output on lead **112**-*i. *

Clock multiplier **102**-*i *is a fractional phrase-locked loop whose output is N times the input frequency. When the control signal on lead **113**-*i *is in the first state:

and when the control signal on lead **113**-*i *is in the second state:

Clock multiplier **102**-*i *comprises: phase detector **201**, low-pass filter **202**, voltage-controlled oscillator **203**, and fractional divider **204**, interconnected as shown.

In accordance with the illustrative embodiment, phase detector **201** outputs a signal to low-pass filter **202** that is based on the phase difference between the 27 MHz clock signal on lead **111** and the output of fractional divider **204**. It will be clear to those skilled in the art how to make and use phase detector **201**.

In accordance with the illustrative embodiment, low-pass filter **202** filters the output of phase detector **201** in well-known fashion. It will be clear to those skilled in the art how to make and use low-pass filter **202**.

In accordance with the illustrative embodiment, voltage-controlled oscillator **203** creates a clock signal whose frequency is dependent on the output of low-pass filter **202** in well-known fashion. It will be clear to those skilled in the art how to make and use voltage-controlled oscillator **203**.

In accordance with the illustrative embodiment, fractional divider **204** divides the output of voltage-controlled oscillator **203** by the value N and passes the decimated signal to phase detector **201**. In accordance with the illustrative embodiment, the value N is represented in fractional divider **204** by a mixed fraction.

In general, when the control signal on lead **113**-*i *is in the first state, the numerator is an integral multiple of 11 and the denominator is an integral power of 2, and when the control signal on lead **113**-*i *is in the second state, the numerator is an integral multiple of 500 and the denominator is an integral multiple of 91. In particular, when the control signal on lead **113**-*i *is in the first state, the numerator is 360,448 and the denominator is 65,536, and when the control signal on lead **113**-*i *is in the second state, the numerator is 360,000 and the denominator is 65,520. Because the difference in the denominators in both states is small and the difference in the numerators in both states is small, the task of designing one circuit to effectively operate with both pairs of numerators and denominators is greatly simplified.

It will be clear to those skilled in the art, after reading this specification, how to make and use alternative embodiments of the present invention that have other combinations of numerators and denominators, such as those presented in Table 1. Note that in each case, the fraction in the first state equals 11/2 exactly and the fraction in the second state equals 500/91 exactly.

TABLE 1 | ||||

Example Numerator and Denominator Pairs | ||||

Control Signal | Control Signal | |||

in First State | in Second State | |||

Numerator | Denominator | Numerator | Denominator | |

704 | 128 | 500 | 91 | |

1,408 | 256 | 1,000 | 182 | |

2,816 | 512 | 2,500 | 455 | |

5,632 | 1,024 | 5500 | 1,001 | |

11,264 | 2,048 | 11,000 | 2,002 | |

22,528 | 4,096 | 22,500 | 4,095 | |

45,056 | 8,192 | 45,000 | 8,190 | |

90,112 | 16,384 | 90,000 | 16,380 | |

180,224 | 32,768 | 180,000 | 32,760 | |

360,448 | 65,536 | 360,000 | 65,520 | |

720,896 | 131,072 | 720,000 | 131,040 | |

1,441,792 | 262,144 | 1,440,000 | 262,080 | |

2,883,584 | 524,288 | 2,880,500 | 524,251 | |

5,767,168 | 1,048,576 | 5,761,000 | 1,048,502 | |

11,534,336 | 2,097,152 | 11,522,500 | 2,097,095 | |

23,068,672 | 4,194,304 | 23,045,500 | 4,194,281 | |

46,137,344 | 8,388,608 | 46,091,000 | 8,388,562 | |

92,274,688 | 16,777,216 | 92,182,500 | 16,777,215 | |

It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. For example, in this Specification, numerous specific details are provided in order to provide a thorough description and understanding of the illustrative embodiments of the present invention. Those skilled in the art will recognize, however, that the invention can be practiced without one or more of those details, or with other methods, materials, components, etc.