Third order sigma-delta modulator

• US 20070018865A1
• Filed: 07/20/2005
• Published: 01/25/2007
• Est. Priority Date: 07/20/2005
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Hung, Chia-Chun, Chang, Long-Xi
• Granted Patent: US 7,253,758 B2
• Time in Patent Office: Days
• US Class Current: 341/143
• CPC Class Codes: H03M 3/424 the quantiser being a multiple bit one
• CPC Class Codes: H03M 3/448 by removing part of the zeroes, e.g. using local feedback loops
• CPC Class Codes: H03M 3/454 with distributed feedback, i.e. with feedback paths from the quantiser output to more than one filter stage
• CPC Class Codes: H03M 7/3026 the quantiser being a multiple bit one
• CPC Class Codes: H03M 7/3035 with provisions for rendering the modulator inherently stable, e.g. by restricting the swing within the loop, by removing part of the zeroes using local feedback loops, by positioning zeroes outside the unit circle causing the modulator to operate in a chaotic regime

Abstract

A third order sigma-delta modulator comprises a first summing unit for receiving an input signal, a first integrator network connected to an output of the first summing unit, a second integrator network for receiving an output of the first integrator network, a second summing unit connected to an output of the second integrator network, a third integrator network connected to an output of the second summing unit, and a feed-forward path from the output of the first integrator network to an input of the second summing unit.

Claims

1. A third order sigma-delta modulator, comprising:

a first summing unit for receiving an input signal;

a first integrator network connected to an output of the first summing unit;

a second integrator network for receiving an output of the first integrator network;

a second summing unit connected to an output of the second integrator network;

a third integrator network connected to an output of the second summing unit; and

a feed-forward path from the output of the first integrator network to an input of the second summing unit.

2. The modulator of claim 1, further comprising one of an analog-to-digital converter (ADC) or a truncator for receiving an output of the third integrator network.

3. The modulator of claim 2, further comprising a digital-to-analog converter (DAC) for receiving an output of the ADC.

4. The modulator of claim 2, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the first summing unit.

5. The modulator of claim 2, further comprising a feedback path connected between an output of the one of ADC or truncator and another input of the second summing unit.

6. The modulator of claim 2, further comprising a third summing unit connected between the first integrator network and the second integrator network.

7. The modulator of claim 6, further comprising a feedback path from an output of the third integrator network to an input of the third summing unit.

8. A third order sigma-delta modulator, comprising:

a first summing unit for receiving an input signal;

a first integrator network connected to an output of the first summing unit;

a second integrator network for receiving an output of the first integrator network;

a second summing unit connected to an output of the second integrator network;

a third integrator network connected to an output of the second summing unit;

a third summing unit connected to an output of the third integrator network; and

a feed-forward path from the output of the second integrator network to an input of the third summing unit.

9. The modulator of claim 8, further comprising one of an analog-to-digital converter (ADC) or a truncator for receiving an output of the third summing unit.

10. The modulator of claim 9, further comprising a digital-to-analog converter (DAC) for receiving an output of the ADC.

11. The modulator of claim 9, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the first integrator network.

12. The modulator of claim 9, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the second integrator network.

13. A third order sigma-delta modulator, comprising:

a first summing unit for receiving an input signal;

a first integrator network connected to an output of the first summing unit;

a second summing unit connected to an output of the first integrator network;

a second integrator network connected to an output of the second summing unit;

a third integrator network for receiving an output of the second integrator network;

a third summing unit connected to an output of the third integrator network; and

a feed-forward path from the output of the first integrator network to an input of the third summing unit.

14. The modulator of claim 13, further comprising one of an analog-to-digital converter (ADC) or a truncator for receiving an output of the third summing unit.

15. The modulator of claim 14, further comprising a digital-to-analog converter (DAC) for receiving an output of the ADC.

16. The modulator of claim 14, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the first integrator network.

17. The modulator of claim 14, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the second integrator network.

18. A third order sigma-delta modulator, comprising:

a first summing unit for receiving an input signal;

a first integrator network connected to an output of the first summing unit;

a second summing unit connected to an output of the first integrator network;

a second integrator network connected to an output of the second summing unit;

a third summing unit connected to an output of the second integrator network;

a third integrator network connected to an output of the third summing unit; and

a feed-forward path from the output of the first summing unit to an input of the third summing unit.

19. The modulator of claim 18, further comprising one of an analog-to-digital converter (ADC) or a truncator for receiving an output of the third integrator network.

20. The modulator of claim 19, further comprising a digital-to-analog converter (DAC) for receiving an output of the ADC.

21. The modulator of claim 19, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the first integrator network.

22. The modulator of claim 19, further comprising a feedback path connected between an output of the one of ADC or truncator and an input of the second integrator network.

23. A method for modulating an input signal to produce an output digital signal, comprising:

providing a first summing unit for receiving the input signal;

connecting a first integrator network to an output of the first summing unit;

providing a second integrator network for receiving an output of the first integrator network;

connecting a second summing unit to an output of the second integrator network;

connecting a third integrator network to an output of the second summing unit; and

feeding forward a modulated signal at the output of the first integrator network to an input of the second summing unit.

24. The method of claim 23, further comprising connecting one of an analog-to-digital converter (ADC) or a truncator to an output of the third integrator network.

25. The method of claim 24, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the first summing unit.

26. The method of claim 24, further comprising feeding back a signal at an output of the one of ADC or truncator to another input of the second summing unit.

27. The method of claim 23, further comprising modulating the input signal in accordance with a noise transfer function (NTF),

NTF=(Z−

1)³/((Z−

1)³+A₃(Z−

1)²+A₁A₃C₁(Z−

1)+A₁A₂A₃)

wherein Z is a Z-transform variable, A₁, A₂ and A₃ are gain factors of the first, second and third integrator networks, respectively, and C₁ is a gain factor of a feed-forward path from the output of the first integrator network to the input of the second summing unit.

28. The method of claim 23, further comprising connecting a third summing unit between the first integrator network and the second integrator network.

29. The method of claim 28, further comprising feeding back a signal at an output of the third integrator network to an input of the third summing unit.

30. A method for modulating an input signal to produce an output digital signal, comprising:

providing a first summing unit for receiving the input signal;

connecting a first integrator network to an output of the first summing unit;

providing a second integrator network for receiving an output of the first integrator network;

connecting a second summing unit to an output of the second integrator network;

connecting a third integrator network to an output of the second summing unit;

connecting a third summing unit to an output of the third integrator network; and

feeding forward a modulated signal at the output of the second integrator network to an input of the third summing unit.

31. The method of claim 30, further comprising connecting one of an analog-to-digital converter (ADC) or a truncator to an output of the third summing unit.

32. The method of claim 31, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the first summing unit.

33. The method of claim 31, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the second summing unit.

34. The method of claim 30, further comprising modulating the input signal in accordance with a noise transfer function (NTF),

NTF=(Z−

1)³/((Z−

1)³+A₃(Z−

1)²+A₁A₂C₁(Z−

1)+A₁A₂A₃)

wherein Z is a Z-transform variable, A₁, A₂ and A₃ are gain factors of the first, second and third integrator networks, respectively, and C₁ is a gain factor of a feed-forward path from the output of the second integrator network to an input of the third summing unit.

35. A method for modulating an input signal to produce an output digital signal, comprising:

providing a first summing unit for receiving the input signal;

connecting a first integrator network to an output of the first summing unit;

connecting a second summing unit to an output of the first integrator network;

connecting a second integrator network to an output of the second summing unit;

providing a third integrator network for receiving an output of the second integrator network;

connecting a third summing unit to an output of the third integrator network; and

feeding forward a modulated signal at the output of the first integrator network to an input of the third summing unit.

36. The method of claim 35, further comprising connecting one of an analog-to-digital converter (ADC) or a truncator to an output of the third summing unit.

37. The method of claim 36, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the first summing unit.

38. The method of claim 36, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the second summing unit.

39. The method of claim 35, further comprising modulating the input signal in accordance with a noise transfer function (NTF),

NTF=(Z−

1)³/((Z−

1)³+A₁C₁(Z−

1)²+A₂A₃(Z−

1)+A₁A₂A₃)

wherein Z is a Z-transform variable, A₁, A₂ and A₃ are gain factors of the first, second and third integrator networks, respectively, and C₁ is a gain factor of a feed-forward path from the output of the first integrator network to an input of the third summing unit.

40. A method for modulating an input signal to produce an output digital signal, comprising:

providing a first summing unit for receiving an input signal;

connecting a first integrator network to an output of the first summing unit;

connecting a second summing unit to an output of the first integrator network;

connecting a second integrator network to an output of the second summing unit;

connecting a third summing unit to an output of the second integrator network;

connecting a third integrator network to an output of the third summing unit; and

feeding forward a modulated signal at the output of the first summing unit to an input of the third summing unit.

41. The method of claim 40, further comprising connecting one of an analog-to-digital converter (ADC) or a truncator to an output of the third integrator network.

42. The method of claim 41, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the first summing unit.

43. The method of claim 41, further comprising feeding back a signal at an output of the one of ADC or truncator to an input of the second summing unit.

44. The method of claim 40, further comprising modulating the input signal in accordance with a noise transfer function (NTF),

NTF=(Z−

1)³/((Z−

1)³+A₃C₁(Z−

1)²+A₂A₃(Z−

1)+A₁A₂A₃)

wherein Z is a Z-transform variable, A₁, A₂ and A₃ are gain factors of the first, second and third integrator networks, respectively, and C₁ is a gain factor of a feed-forward path from the output of the first summing unit to an input of the third summing unit.