Single side band transmitter having reduced DC offset

• US 20030232605A1
• Filed: 06/18/2002
• Published: 12/18/2003
• Est. Priority Date: 06/18/2002
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Peng, Meng-An
• Granted Patent: US 7,103,327 B2
• Time in Patent Office: Days
• US Class Current: 455/109
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence

Abstract

A single side band transmitter having reduced DC offset includes a current source modulation module, a current mirror module, a 1^st mixing module, a 2^nd mixing module, a summing module, and a power amplifier. The current source module is operably coupled to modulate, in accordance with a modulation protocol (e.g., FSK) data to produce an in-phase current component and a quadrature current component. The current mirror module is operably coupled to mirror the in-phase current component to produce a mirrored in-phase current component and is also operably coupled to mirror the quadrature current component to produce a mirrored quadrature current component. The 1^st mixing module is operably coupled to mix the mirrored in-phase current component with an in-phase current component of a local oscillation to produce a 1^st mixed current signal. The 2^nd mixing module is operably coupled to mix the mirrored quadrature current component with a quadrature component of the local oscillation to produce a 2^nd mixed current signal. The summing module is operably coupled to sum the 1^st and 2^nd mixed current signals to produce an up converted signal. The power amplifier amplifies the up converted signal prior to transmission as a radio frequency signal.

Claims

1. A single side band transmitter comprises:

current source modulation module operably coupled to modulated, in accordance with a modulation protocol, data to produce an in-phase current component and a quadrature current component;

current mirror module operably coupled to mirror the in-phase current component to produce a mirrored in-phase current component and operably coupled to mirror the quadrature current component to produce a mirrored quadrature current component;

first mixing module operably coupled to mix the mirrored in-phase current component with an in-phase component of a local oscillation to produce a first mixed signal;

second mixing module operably coupled to mix the mirrored quadrature current component with a quadrature component of the local oscillation to produce a second mixed signal;

summing module operably coupled to sum the first and second mixed signals to produce an up-converted signal; and

power amplifier operably coupled to amplify the up-converted signal to produce a radio frequency signal.

2. The single side band transmitter of claim 1, wherein the module protocol comprises at least one of:

frequency shift keying, binary phase shift keying, quadrature phase shift keying, quadrature amplitude modulation, and frequency modulation.

3. The single side band transmitter of claim 1, wherein the current mirror module further comprises:

first current mirror circuit that includes a first transistor and a first low pass filter, wherein the first transistor substantially matches an input transistor of the first mixing module, and wherein the first low pass filter is operably coupled to the first transistor and the input transistor of the first mixing module; and

second current mirror circuit that includes a second transistor and a second low pass filter, wherein the second transistor substantially matches an input transistor of the second mixing module, and wherein the second low pass filter is operably coupled to the second transistor and the input transistor of the second mixing module.

4. The single side band transmitter of claim 1, wherein the current source modulation module further comprises:

modulator operably coupled to modulate the data to produce a digital in-phase component and a digital quadrature component;

first digital to analog conversion module operably coupled to convert the digital in-phase component into the in-phase current component; and

second digital to analog conversion module operably coupled to convert the digital quadrature component into the quadrature current component.

5. The single side band transmitter of claim 4 further comprises:

the modulator producing a differential digital in-phase component and a differential digital quadrature component;

the first digital to analog conversion module including a first digital to analog converter for converting one leg of the differential digital in-phase component into one leg of a differential in-phase current component and a second digital to analog converter for converting another leg of the differential digital in-phase component into another leg of the differential in-phase current component; and

the second digital to analog conversion module including a third digital to analog converter for converting one leg of the differential digital quadrature component into one leg of a differential quadrature current component and a fourth digital to analog converter for converting another leg of the differential digital quadrature component into another leg of the differential quadrature current component.

6. The single side band transmitter of claim 5, wherein the current mirror module further comprises:

first current mirror circuit that includes a first transistor and a first low pass filter, wherein the first transistor substantially matches a first input transistor of the first mixing module, and wherein the first low pass filter is operably coupled to the first transistor and the first input transistor of the first mixing module;

second current mirror circuit that includes a second transistor and a second low pass filter, wherein the second transistor substantially matches a second input transistor of the first mixing module, and wherein the second low pass filter is operably coupled to the second transistor and the second input transistor of the first mixing module;

third current mirror circuit that includes a third transistor and a third low pass filter, wherein the third transistor substantially matches a first input transistor of the second mixing module, and wherein the third low pass filter is operably coupled to the third transistor and the first input transistor of the second mixing module; and

fourth current mirror circuit that includes a fourth transistor and a fourth low pass filter, wherein the fourth transistor substantially matches a second input transistor of the second mixing module, and wherein the fourth low pass filter is operably coupled to the fourth transistor and the second input transistor of the second mixing module.

7. A method for reduced DC offset in single side band transmissions, the method comprises:

modulating, in accordance with a modulation protocol, data to produce an in-phase current component and a quadrature phase current component;

maintaining the in-phase current component and the quadrature phase current component in a current domain when mixing with a local oscillation to produce a first mixed signal and a second mixed signal;

summing the first and second mixed signals to produce a radio frequency signal; and

amplifying the radio frequency signal prior to transmission.

8. The method of claim 7, wherein the maintaining the in-phase current component and the quadrature current component in the current domain further comprises:

mirroring current of the in-phase current component to produce a mirrored in-phase current component;

mixing the mirrored in-phase current component with an in-phase component of the local oscillation to produce the first mixed signal;

mirroring the quadrature current component to produce a mirrored quadrature current component; and

mixing the mirrored quadrature current component with a quadrature component of the local oscillation to produce the second mixed signal.

9. The method of claim 8, wherein the maintaining the in-phase current component and the quadrature current component in the current domain further comprises:

low pass filtering the mirrored in-phase current component prior to the mixing; and

low pass filtering the mirrored quadrature current component prior to the mixing.

10. The method of claim 7, wherein the modulating the data further comprises at least one of:

modulating the data in accordance with frequency shift keying;

modulating the data in accordance with binary phase shift keying;

modulating the data in accordance with quadrature phase shift keying;

modulating the data in accordance with quadrature amplitude modulation; and

modulating the data in accordance with frequency modulation.

11. The method of claim 7, wherein the modulating the incoming data further comprises:

modulating the data to produce a digital in-phase component and a digital quadrature component;

converting the digital in-phase component into the in-phase current component; and

converting the digital quadrature component into the quadrature current component.

12. The method of claim 7, wherein the modulating the incoming data further comprises:

producing a differential digital in-phase component and a differential digital quadrature component;

converting one leg of the differential digital in-phase component into one leg of a differential in-phase current component;

converting another leg of the differential digital in-phase component into another leg of the differential in-phase current component;

converting one leg of the differential digital quadrature component into one leg of a differential quadrature current component; and

converting another leg of the differential digital quadrature component into another leg of the differential quadrature current component.

13. The method of claim 12 further comprises:

mirroring current of the one leg of the differential in-phase current component to produce a first mirrored in-phase current component;

mixing the first mirrored in-phase current component with one leg of an in-phase component of the local oscillation to produce one leg of the first mixed signal;

mirroring current of the another leg of the differential in-phase current component to produce a second mirrored in-phase current component;

mixing the second mirrored in-phase current component with another leg of the in-phase component of the local oscillation to produce another leg of the first mixed signal;

mirroring the one leg of the quadrature current component to produce a first mirrored quadrature current component;

mixing the first mirrored quadrature current component with one leg of a quadrature component of the local oscillation to produce one leg of the second mixed signal;

mirroring the another leg of the quadrature current component to produce a second mirrored quadrature current component; and

mixing the second mirrored quadrature current component with another leg of the quadrature component of the local oscillation to produce another leg of the second mixed signal.

14. The method of claim 13 further comprises:

low pass filtering the first mirrored in-phase current component prior to mixing;

low pass filtering the second mirrored in-phase current component prior to mixing;

low pass filtering the first mirrored quadrature current component prior to mixing; and

low pass filtering the second quadrature current component prior to mixing.

15. A single side band transmitter comprises:

means for modulating, in accordance with a modulation protocol, data to produce an in-phase current component and a quadrature phase current component;

means for maintaining the in-phase current component and the quadrature phase current component in a current domain when mixing with a local oscillation to produce a first mixed signal and a second mixed signal;

means for summing the first and second mixed signals to produce a radio frequency signal; and

means for amplifying the radio frequency signal prior to transmission.

16. The single side band transmitter of claim 15, wherein the means for maintaining the in-phase current component and the quadrature current component in the current domain further functions to:

mirror current of the in-phase current component to produce a mirrored in-phase current component;

mix the mirrored in-phase current component with an in-phase component of the local oscillation to produce the first mixed signal;

mirror the quadrature current component to produce a mirrored quadrature current component; and

mix the mirrored quadrature current component with a quadrature component of the local oscillation to produce the second mixed signal.

17. The single side band transmitter of claim 16, wherein the means for maintaining the in-phase current component and the quadrature current component in the current domain further functions to:

low pass filter the mirrored in-phase current component prior to the mixing; and

low pass filter the mirrored quadrature current component prior to the mixing.

18. The single side band transmitter of claim 15, wherein the means for modulating the data further functions to perform at least one of:

modulating the data in accordance with frequency shift keying;

modulating the data in accordance with binary phase shift keying;

modulating the data in accordance with quadrature phase shift keying;

modulating the data in accordance with quadrature amplitude modulation; and

modulating the data in accordance with frequency modulation.

19. The single side band transmitter of claim 15, wherein the means for modulating the incoming data further functions to:

modulate the data to produce a digital in-phase component and a digital quadrature component;

convert the digital in-phase component into the in-phase current component; and

convert the digital quadrature component into the quadrature current component.

20. The single side band transmitter of claim 15, wherein the means for modulating the incoming data further functions to:

produce a differential digital in-phase component and a differential digital quadrature component;

convert one leg of the differential digital in-phase component into one leg of a differential in-phase current component;

convert another leg of the differential digital in-phase component into another leg of the differential in-phase current component;

convert one leg of the differential digital quadrature component into one leg of a differential quadrature current component; and

convert another leg of the differential digital quadrature component into another leg of the differential quadrature current component.

21. The single side band transmitter of claim 20, wherein the means for maintaining the in-phase current component and the quadrature phase current component in a current domain further functions to:

mirror current of the one leg of the differential in-phase current component to produce a first mirrored in-phase current component;

mix the first mirrored in-phase current component with one leg of an in-phase component of the local oscillation to produce one leg of the first mixed signal;

mirror current of the another leg of the differential in-phase current component to produce a second mirrored in-phase current component;

mix the second mirrored in-phase current component with another leg of the in-phase component of the local oscillation to produce another leg of the first mixed signal;

mirror the one leg of the quadrature current component to produce a first mirrored quadrature current component;

mix the first mirrored quadrature current component with one leg of a quadrature component of the local oscillation to produce one leg of the second mixed signal;

mirror the another leg of the quadrature current component to produce a second mirrored quadrature current component; and

mix the second mirrored quadrature current component with another leg of the quadrature component of the local oscillation to produce another leg of the second mixed signal.

22. The single side band transmitter of claim 21, wherein the means for maintaining the in-phase current component and the quadrature phase current component in a current domain further functions to:

low pass filter the first mirrored in-phase current component prior to mixing;

low pass filter the second mirrored in-phase current component prior to mixing;

low pass filter the first mirrored quadrature current component prior to mixing; and

low pass filter the second quadrature current component prior to mixing.