Circuit with noise shaper

Abstract

In an embodiment, a circuit comprising an oscillator is provided. The oscillator is controlled based on a feedback value and an input reference value. The feedback value or the reference value or both are generated using noise shaping.

What is claimed is: 
     
         1 . A circuit, comprising:
 an oscillator configured to generate an output signal having a frequency,   a feedback value generator coupled to said oscillator configured to generate a feedback value depending on said output signal,   a reference value generator comprising a noise shaper circuit configured to generate a noise shaped reference value depending on a predetermined value,   a combiner configured to combine said noise shaped reference value and said feedback value and to output a combined signal, and   a loop filter configured to generate a control signal to control said oscillator based on said combined signal,   wherein said reference value generator is further configured to generate said noise shaped reference value independent of signal values in a path from said combiner to said oscillator via said loop filter and independent of signal values in a path from said oscillator to said combiner via said feedback value generator.   
     
     
         2 . The circuit of  claim 1 ,
 wherein said predetermined value determines a relationship between a frequency of a reference clock and said frequency of said output signal.   
     
     
         3 . The circuit of  claim 1 ,
 wherein said predetermined value comprises at least one first value and at least one second value,   wherein said reference value comprises at least one first reference value and at least one second reference value,   wherein said reference value generator is configured to generate said first reference value depending on said first value without using said noise shaper circuit and to generate said second reference value depending on said at least one second value using said noise shaper circuit.   
     
     
         4 . The circuit of  claim 1 ,
 wherein said loop filter comprises a modulator configured to modulate said control signal based on said output signal.   
     
     
         5 . A circuit, comprising:
 an oscillator configured to generate an output signal, said output signal having a frequency,   a feedback value generator coupled to said oscillator, said feedback value generator comprising a noise shaper circuit and being configured to generate a noise-shaped feedback value depending on said output signal, wherein said feedback value generator comprises a phase shifter circuit configured to shift a phase of said output signal controlled by said noise shaper circuit and to output a phase shifted output signal, and a phase quantizer configured to receive said phase shifted output signal,   a reference value generator configured to generate a reference value depending on a predetermined value,   a combiner configured to combine said reference value and said noise-shaped feedback value, and to output a combined signal, and   a loop filter configured to generate a control signal to control said oscillator depending on said combined signal.   
     
     
         6 . The circuit of  claim 5 ,
 wherein said oscillator is a digitally controlled oscillator.   
     
     
         7 . The circuit of  claim 5 , further comprising a differentiator coupled between said phase quantizer and said combiner. 
     
     
         8 . The circuit of  claim 5 ,
 wherein said loop filter comprises a modulator configured to modulate said control signal based on said output signal.   
     
     
         9 . A circuit, comprising:
 an oscillator comprising a control input and an output,   a reference clock input,   a phase quantizer comprising an input, an output and a clock input, said input of said phase quantizer being coupled with said output of said oscillator and said clock input of said phase quantizer being coupled with said reference clock input,   a first storage and a second storage,   a noise shaper circuit comprising an input, an output and a clock input, said input of said noise shaper being coupled with said second storage,   a combiner comprising a first input, a second input, a third input and an output, said first input of said combiner being coupled with said first storage, said second input of said combiner being coupled with said output of said noise shaper and said third input of said combiner being coupled with said output of said phase quantizer, and   a loop filter comprising an input, an output and a clock input, said clock input of said loop filter being coupled with said reference clock input, said output of said loop filter being coupled with said control input of said oscillator and said input of said loop filter being coupled with said output of said combiner.   
     
     
         10 . The circuit of  claim 9 ,
 wherein said combiner comprises at least one subtractor.   
     
     
         11 . The circuit of  claim 9 ,
 wherein said first storage stores an integer value and said second storage stores a value selected from the interval from 0 and 1, including 0.   
     
     
         12 . The circuit of  claim 9 , further comprising a first integrator coupled between said first storage and said first input of said combiner and a second integrator coupled between said output of said noise shaper and said second input of said combiner. 
     
     
         13 . The circuit of  claim 9 , further comprising a differentiator coupled between said output of said phase quantizer and said third input of said combiner. 
     
     
         14 . The circuit of  claim 9 ,
 further comprising a sampling circuit comprising an input, a clock input and an output, wherein said clock input of said sampling circuit is coupled with said output of said oscillator, wherein said input of said sampling circuit is coupled with said reference clock input and wherein said output of said sampling circuit is coupled with at least one clock input selected from the group comprising said clock input of said noise shaper circuit and said clock input of said loop filter.   
     
     
         15 . A circuit, comprising:
 an oscillator comprising an output and a control input,   a phase shifter circuit comprising an input, an output and a control input, said input of said phase shifter circuit being coupled with said output of said oscillator,   a noise shaper circuit comprising an output and a clock input, said output of said noise shaper circuit being coupled with said control input of said phase shifter circuit and said clock input of said noise shaper circuit being coupled with a reference clock input,   a phase quantizer comprising an input and an output, said input of said phase quantizer being coupled with said output of said phase shifter,   a storage comprising an output,   a combiner comprising a first input, a second input and an output, said first input of said combiner being coupled with said output of said storage and said second input of said combiner being coupled with said output of said phase quantizer, and   a loop filter comprising an input and an output, said input of said loop filter being coupled with said output of said combiner and said output of said loop filter being coupled with said control input of said oscillator.   
     
     
         16 . The circuit of  claim 15 ,
 wherein said combiner comprises at least one subtractor.   
     
     
         17 . The circuit of  claim 15 ,
 wherein said loop filter comprises a clock input coupled with said reference clock input and wherein said phase quantizer comprises a clock input coupled with said reference clock input.   
     
     
         18 . The circuit of  claim 15 , further comprising a differentiator coupled between said output of said phase quantizer and said second input of said combiner. 
     
     
         19 . The circuit of  claim 15 , further comprising an integrator coupled between said output of said storage and said input of said combiner. 
     
     
         20 . A method, comprising:
 generating an output signal, said output signal having a frequency,   generating a feedback value based on said output signal,   generating a reference value based on a reference clock and a predetermined value, and   controlling said generation of said output signal based on said reference value and said feedback value,   wherein said generating a feedback value, said generating a reference value, or both, comprises performing a noise shaping.   
     
     
         21 . The method of  claim 20 , further comprising setting said predetermined value to determine a relationship between said frequency of said output signal and a frequency of said reference clock. 
     
     
         22 . The method of  claim 20 ,
 wherein said generating a feedback value comprises said performing of said noise shaping,   wherein said generating a feedback value comprises shifting a phase of said output signal based on said noise shaping.   
     
     
         23 . The method of  claim 20 ,
 wherein said generating a reference value comprises said performing of said noise shaping,   wherein said generating a reference value comprises performing said noise shaping based on a non-integer part of said predetermined value.   
     
     
         24 . The method of  claim 20 ,
 further comprising deactivating said noise shaping if said predetermined value is an integer value.   
     
     
         25 . The method of  claim 20 ,
 wherein said generating a reference value comprises said performing of said noise shaping,   wherein said generating said reference value is performed independent of said feedback value.