Pulse modulation power amplifier with enhanced cascade control method

• US 6,297,692 B1
• Filed: 06/24/1999
• Issued: 10/02/2001
• Est. Priority Date: 10/31/1996
• Status: Expired due to Term

• Current Assignee: Bang & Olufsen A/S, Karsten Nielsen
• Original Assignee: Bang & Olufsen A/S, Karsten Nielsen
• Inventors: Nielsen, Karsten
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/297,058
• Time in Patent Office: 831 Days
• Field of Search: 330/10, 330/207 A, 330/251, 330/207 R
• US Class Current: 330/10
• CPC Class Codes: H03F 1/083 in transistor amplifiers H03F1/10 - H03F1/22 take precedence
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers

Abstract

A digital switching power amplifier with Multivariable Enhanced Cascade Controlled (MECC) includes a modulator, a switching power stage and a low pass filter. In the first preferred embodiment an enhanced cascade control structure local to the switching power stage is added, characterised by having a single local feedback path A (7) with a lowpass characteristic and local forward blocks B₁ or B (3, 4). The leads to a much improved system with a very low sensitivity to errors in the switching power stage. In the second preferred embodiment of the invention the control structure is extended with a global structure composed of a single feed-back path C (8) and forward paths blocks D1 or D (1, 2). This provides further improvements and a very low sensitivity to load variations and filter errors. Both MECC embodiments are characterised by being simple in implementation, stable and extendible by adding/removing simple local (3) or global (1) forward path blocks. A third embodiment of the invention is a controlled self-oscillating pulse modulator, characterised by first a non-hysteresis comparator as modulator and second by a higher order oscillating loop realized in both forward path B1 and feedback path A to determine stable self-oscillating conditions. An implemented 250W example MECC digital power amplifier has proven superior performance in terms of audio performance (0.005% distortion, 115 dB dynamic range) and efficiency (92%).

Claims

1. Pulse modulation power amplifier for the audio frequency range, comprising:

a pulse modulator, and a switching stage for amplifying the modulated signal, the output of which is low pass filtered in a demodulation filter for obtaining an analog output to feed to a consumer, wherein a first negative feedback is introduced from the switching stage output to one or several feedback loops feeding into one or several forward paths preceding the modulator, at least one of said feedback loops comprising a feedback path with a phase characteristic such that a pole in the demodulation filter is compensated.

2. A power amplifier according to claim 1, wherein a single feedback path is used for all feedback loops.

3. A power amplifier according to claim 2, wherein each feedback loop has stable first order open loop characteristics.

4. A power amplifier according to claim 1, wherein a second feedback is established from the output of the demodulation filter to one or several forward paths.

5. A power amplifier according to claim 4, wherein said first feedback includes at least one feedback loop from the switching stage to a first group of at least one forward path, and said second feedback includes at least one feedback loop from the demodulation filter output to a second group of at least one forward path, preceding said first group.

6. A power amplifier according to claim 5, wherein a single feedback path is used for all feedback loops in said second feedback.

7. A power amplifier according to claim 6, wherein each loop has stable first order open loop characteristics.

8. A power amplifier according to claim 1, wherein the pulse modulator is a controlled self-oscillating modulator comprising a non-hysteresis comparator for pulse modulation and a higher order oscillating loop realized by means of at least two poles.

9. A power amplifier according to claim 1, wherein the pulse modulator is a carrier based pulse modulator.

10. A power amplifier according to claim 1, further comprising:

additional secondary filtering circuitry at the amplifier output for further elimination of switching components.

11. A power amplifier according to claim 1, further comprising:

an input filter to shape the overall amplifier response in frequency and time.

12. A pulse modulation power amplifier for the audio frequency range, comprising:

a pulse modulator, and a switching stage for amplifying the modulated signal, the output of which is low pass filtered in a demodulation filter for obtaining an analog output to feed to a consumer, wherein a first negative feedback is introduced from the switching stage output to one or several forward paths preceding the modulator, and wherein a second feedback is established from the output of the demodulation filter to one or several forward paths.

13. A power amplifier according to claim 12, wherein said first feedback includes at least one feedback loop from the switching stage to a first group of at least one forward path, and said second feedback includes at least one feedback loop from the demodulation filter output to a second group of at least one forward path, preceding said first group.

14. A power amplifier according to claim 13, wherein a single feedback path is used for all feedback loops in said first feedback.

15. A power amplifier according to claim 14, wherein each loop has stable first order open loop characteristics.

16. A power amplifier according to claim 13, further wherein a single feedback path is used for all feedback loops in said second feedback.

17. A power amplifier according to claim 16, wherein each loop has stable first order open loop characteristics.

18. A power amplifier according to claim 12, wherein the pulse modulator is a controlled self-oscillating modulator, comprising a non-hysteresis comparator for pulse modulation and a higher order oscillating loop realized by means of at least two poles.

19. A power amplifier according to claim 12, wherein the pulse modulator is a carrier based pulse modulator.

20. A power amplifier according to claim 12, further comprising:

additional secondary filtering circuitry at the amplifier output for further elimination of switching components.

21. A power amplifier according to claim 12, further comprising:

an input filter to shape the overall amplifier response in frequency and time.

22. A controlled self-oscillating modulator comprising a non-hysteresis comparator for pulse modulation of a switching stage, and a voltage feedback loop from the switching stage to the comparator, said feedback loop securing stable oscilating conditions by means of at least two polcs, wherein said feedback loop comprises a feedback path providing a feedback signal to a forward path, said feedback signal being superposed with a reference signal in the forward path, said feedback path comprising at least one pole, and said forward path comprising at least one pole.

23. A controlled self-oscillating modulator according to claim 22, wherein said feedback path comprises at least two poles, one of said poles compensating a pole in a demodulation filter connected to the switching stage.

24. A controlled self-oscillating modulator according to claim 23, wherein said feedback path and said forward path each further comprise a ploe at the desired oscillating frequency.