Method and apparatus for high density pulse density modulation
A method and system for high density pulse density modulation is disclosed. In accordance with the present disclosure, a modulation function is split in to two band limited streams using a complementary pair of non-linear functions. More specifically, one bitstream definition contains the peaks of the original function while the other bitstream contains a soft clipping version of the original bitstream. The bitstreams are applied to a pair of switching amplifiers, and the bitstreams can be combined again to reconstruct the original function. The method in accordance with the present disclosure limits the amount of input power necessary to achieve higher output power, lowers operating voltage and improves power amplifier efficiency.
1. A method for high density pulse density modulation, comprising:
receiving a bitstream;
splitting the bitstream in to two complementary streams based on whether a modulation level exceeds a limiting value v, wherein a first one of the two complementary streams contains a soft clipped stream of the received bitstream limited by the limiting value v, and a second one of the two complementary streams contains only extracted portions of the received bitstream, wherein when a portion of the received bitstream is greater than v, said portion of the received bitstream is represented based on a difference of said portion of the received bitstream and the limiting value v in the second one of the two complementary streams, and wherein when a portion of the received bitstream is less than −v, said portion of the received bitstream is represented based on a sum of said portion of the received bitstream and the limiting value v in the second one of the two complementary streams; and
amplifying each of the two complementary streams independently for transmission.
2. The method of claim 1 , wherein the soft clipped stream contained in the first one of the two complementary streams is compressed.
3. The method of claim 1 , wherein the limiting value is a static value.
4. The method of claim 1 , wherein the limiting value is dynamically adjustable.
5. The method of claim 1 , wherein the limiting value is determined based on a function.
6. The method of claim 1 , further comprising:
amplifying each of the two complementary streams independently for transmission.
7. A system for high density pulse density modulation, comprising:
a bitstream generator configured for generating a bitstream;
a split mechanism communicatively coupled with the bitstream generator, the split mechanism configured for splitting the bitstream in to two complementary streams based on whether a modulation level exceeds a limiting value v, wherein a first one of the two complementary streams contains a soft clipped stream of the received bitstream limited by the limiting value v, and a second one of the two complementary streams contains only extracted portions of the received bitstream, wherein when a portion of the received bitstream is greater than v, said portion of the received bitstream is represented based on a difference of said portion of the received bitstream and the limiting value v in the second one of the two complementary streams, and wherein when a portion of the received bitstream is less than −v, said portion of the received bitstream is represented based on a sum of said portion of the received bitstream and the limiting value v in the second one of the two complementary streams;
a first power amplifier configured for amplifying the first one of the two complementary streams; and
a second power amplifier configured for amplifying the second one of the two complementary streams.
8. The system of claim 7 , wherein the split mechanism is configured to compress the soft clipped stream in the first one of the two complementary streams.
9. The system of claim 7 , wherein the limiting value is a static value.
10. The system of claim 7 , wherein the limiting value is dynamically adjustable.
11. The system of claim 7 , wherein the limiting value is determined based on a function.
12. The system of claim 7 , wherein the first and second power amplifiers operate independently with respect to each other.
13. The system of claim 7 , wherein the first and second power amplifiers are switch-mode power amplifiers.
14. The system of claim 13 , wherein the first and second power amplifiers are Class-S power amplifiers.
15. A bitstream splitting apparatus, comprising:
a processor; and
a computer-readable device having computer-executable instructions for splitting a bitstream in to two complementary streams based on whether a modulation level exceeds a limiting value v, wherein a first one of the two complementary streams contains a soft clipped stream of the bitstream limited by the limiting value v, and a second one of the two complementary streams contains only extracted portions of the bitstream, wherein when a portion of the received bitstream is greater than v, said portion of the received bitstream is represented based on a difference of said portion of the received bitstream and the limiting value v in the second one of the two complementary streams, and wherein when a portion of the received bitstream is less than −v, said portion of the received bitstream is represented based on a sum of said portion of the received bitstream and the limiting value v in the second one of the two complementary streams.
16. The bitstream splitting apparatus of claim 15 , wherein the soft clipped stream contained in the first one of the two complementary streams is compressed.
17. The bitstream splitting apparatus of claim 15 , wherein the limiting value is a static value.
18. The bitstream splitting apparatus of claim 15 , wherein the limiting value is dynamically adjustable.
19. The bitstream splitting apparatus of claim 15 , wherein the limiting value is determined based on a function.
20. The bitstream splitting apparatus of claim 15 , wherein the computer-readable device further includes computer-executable instructions for providing each of the two complementary streams to an independently operating power amplifier.