Modulation system

• US 20040246060A1
• Filed: 06/09/2003
• Published: 12/09/2004
• Est. Priority Date: 06/09/2003
• Status: Active Grant

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Varis, Jukka, Rosnell, Seppo
• Granted Patent: US 6,975,177 B2
• Time in Patent Office: Days
• US Class Current: 332/109
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 1/0205 in transistor amplifiers
• 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
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation

Abstract

In a modulation system,.in order to provide a two-level signal with a desired modulation which is suited to be amplified by a switching mode power amplifier, the modulation system may include a first constant envelope modulator modulating a signal according to a first control signal, a second constant envelope modulator modulating a signal according to a second control signal, and a combining portion combining the output signal of the first and said second constant envelope modulator to a single, two-level pulse-width-modulated signal. The information which is to be represented by the modulation of the single, two-level pulse-width-modulated signal is coded in the first and the second control signals. The invention relates equally to a corresponding method for generating a modulated signal.

Claims

1. A modulation system comprising:

a first constant envelope modulator modulating a signal according to a first control signal;

a second constant envelope modulator modulating a signal according to a second control signal; and

a combining portion combining output signals of said first and said second constant envelope modulators to a single, two-level pulse-width-modulated signal, wherein information for representation by a modulation of said single, two-level pulse-width-modulated signal is coded in said first and said second control signals.

2. The modulation system according to claim 1, further comprising a processing portion, which processing portion receives an in-phase component I and a quadrature component Q of an analog modulation signal containing said information which is for representation by a modulation of said single, two-level pulse-width-modulated signal, and which processing portion calculates said first control signal as

3. The modulation system according to claim 1, wherein a center frequency of said first constant envelope modulator and of said second constant envelope modulator is half of a desired center frequency of said single, two-level pulse-width-modulated signal.

4. The modulation system according to claim 1, wherein said first and said second constant envelope modulators are analog constant envelope modulators modulating a sinusoidal signal in phase based on said first and said second control signal.

5. The modulation system according to claim 4, further comprising a first limiter converting the output signal of said first constant envelope modulator into a two-level signal, before it is provided to said combining unit, and a second limiter converting the output signal of said second constant envelope modulator into a two-level signal, before it is provided to said combining unit.

6. The modulation system according to claim 1, wherein said first and said second constant envelope modulators are digital constant envelope modulators outputting a respective pulsed signal, in which the transition times are modulated based on said first and said second control signals, respectively.

7. The modulation system according to claim 1, wherein said combining unit comprises a logic exclusive-or circuit.

8. The modulation system according to claim 1, wherein said combining unit comprises a logic exclusive-nor circuit.

9. The modulation system according to claim 1, wherein said combining unit comprises an analog mixer.

10. The modulation system according to claim 1, further comprising a switching mode power amplifier amplifying said single, two-level pulse-width-modulated signal provided by said combining unit.

11. The modulation system according to claim 10, further comprising at least one of a bandpass filter and a lowpass filter for generating a variable envelope signal out of said amplified single, two-level, pulse-width-modulated signal provided by said switching mode power amplifier.

12. A method for generating a modulated signal, said method comprising:

modulating a signal according to a first control signal to obtain a first modulated constant envelope signal;

modulating a signal according to a second control signal to obtain a second modulated constant envelope signal; and

combining said first modulated constant envelope signal and said second modulated constant envelope signal into a single, two-level pulse-width-modulated signal, wherein information for representation by a modulation of said single, two-level pulse-width-modulated signal is coded in said first control signal and said second control signal.

13. The method according to claim 12, wherein said first control signal is calculated as

14. The method according to claim 12, wherein a center frequency of said first constant envelope signal and of said second constant envelope signal before modulation is selected to be half of a desired center frequency of said single, two-level pulse-width-modulated signal.

15. The method according to claim 12, wherein said first and said second constant envelope signals are sinusoidal signals which are modulated in phase based on said first and said second control signal.

16. The method according to claim 12, further comprising converting said first modulated constant envelope signal and said second modulated constant envelope signal into respective two-level signals before combining them.

17. The method according to claim 12, wherein said first modulated constant envelope signal and said second modulated constant envelope signal are pulsed constant envelope signals, in which the transition times are modulated based on said first control signal and said second control signal.

18. The method according to claim 12, further comprising amplifying said single, two-level pulse-width-modulated signal by means of a switching mode power amplifier.

19. The method according to claim 18, further comprising generating a variable envelope signal by filtering said amplified single, two-level, pulse-width-modulated signal.