Radio frequency modulator and method thereof
A radio frequency (RF) modulator includes: converting means for up-converting a first and second baseband signals into a first and second up-converted signals with a reference clock, wherein a phase difference between the first and second baseband signals substantially equals 180°/N; and combining means for combining the first and second up-converted signals to generate an output signal.
1. A radio frequency (RF) modulator, comprising:
means for up-converting a first and second baseband signals into a first and second up-converted signals with a reference clock, wherein a phase difference between the first and second baseband signals substantially equals 180°/N such that N-th order inter-modulation tone in the output signal is reduced; and
means for combining the first and second up-converted signals to generate an output signal including the reduced N-th order inter-modulation tone and a main signal.
2. The RF modulator of claim 1 , wherein the means for up-converting the first and second baseband signals into the first and second up-converted signals with the reference clock comprises:
a first transconducting circuit, for transforming the first baseband signal into a first transconducted signal;
a first mixer, for mixing the first transconducted signal with the reference clock to generate the first up-converted signal;
a second transconducting circuit, for transforming the second baseband signal into a second transconducted signal; and
a second mixer, for mixing the second transconducted signal with the reference clock to generate the second up-converted signal.
3. The RF modulator of claim 1 , further comprising:
phase shifting means for receiving a baseband input signal to generate the first and second baseband signals; and
amplification means for amplifying the first and second up-converted signals before the first and second up-converted signals being combined by the means for combining the first and second up-converted signals to generate the output signal.
4. The RF modulator of claim 3 , wherein the phase shifting means is embedded in a baseband chip or is implemented by a physical circuitry outside the baseband chip.
5. The RF modulator of claim 3 , wherein the first amplified signal comprises a first specific amplified signal, and the second amplified signal comprises a second specific amplified signal; and when the first specific amplified signal and the second specific amplified signal are N-th order inter-modulation tones of the first amplified signal and the second amplified signal, respectively, the phase shifting means sets the phase difference between the first and the second baseband signals to be substantially 180°/N.
6. The RF modulator of claim 3 , wherein the baseband input signal comprises an I-channel input signal and a Q-channel input signal, and the phase shifting means is operated in current mode to generate the first and the second baseband signals with the phase difference.
7. The RF modulator of claim 3 , wherein the baseband input signal comprises an I-channel input signal and a Q-channel input signal, and the phase shifting means is operated in voltage mode to generate the first and the second baseband signals with the phase difference.
8. The RF modulator of claim 3 , further comprising:
adjusting means, for detecting the output signal to generate an adjusting signal to the phase shifting means for adjusting at least one phase of the first and second baseband signals.
9. The RF modulator of claim 8 , wherein the adjusting means comprises:
a power detector, for detecting a power of the output signal to generate a detected value; and
a digital-to-analog converter, for converting the detected value into the adjusting signal;
wherein when the adjusting means detects that a power corresponding to one of the first specific amplified signal and the second specific amplified signal in the output signal reaches a predetermined power level, the adjusting means outputs the adjusting signal to the shifting means.
10. A signal processing apparatus, comprising:
a first up-converter, receiving a first baseband signal with a first phase and receiving a reference clock, for up-converting the first baseband signal to generate a first up-converted signal with the reference clock;
a second up-converter, receiving a second baseband signal with a second phase different from the first phase and receiving the reference clock, for up-converting the second baseband signal to generate a second up-converted signal with the reference clock;
a first amplifier, coupled to the first up-converter, for amplifying the first up-converted signal to generate a first amplified signal;
a second amplifier, coupled to the second up-converter, for amplifying the second up-converted signal to generate a second amplified signal; and
a combining circuit, coupled to the first amplifier and the second amplifier, for combining the first amplified signal and the second amplified signal to generate an output signal including a reduced N-th order inter-modulation tone and a main signal;
wherein a phase difference between the first phase and the second phase substantially equals 180°/N such that N-th order inter-modulation tone in the output signal is reduced.
11. The signal processing apparatus of claim 10 , wherein the first up-converter comprises:
a first transconducting circuit, receiving the first baseband signal, for transforming the first baseband signal into a first transconducted signal; and
a first mixer, coupled to the first transconducting circuit and the reference clock, for mixing the first transconducted signal with the reference clock to generate the first up-converted signal; and
the second up-converter comprises:
a second transconducting circuit, receiving the second baseband signal, for transforming the second baseband signal into a second transconducted signal; and
a second mixer, coupled to the second transconducting circuit and the reference clock, for mixing the second transconducted signal with the reference clock to generate the second up-converted signal.
12. The signal processing apparatus of claim 10 , further comprising:
a phase shifter, coupled to the first up-converter and the second up-converter, for receiving a baseband input signal and generating the first baseband signal and the second baseband signal according to the baseband input signal.
13. The signal processing apparatus of claim 12 , wherein the first amplified signal comprises a first specific amplified signal, and the second amplified signal comprises a second specific amplified signal; and when the first specific amplified signal and the second specific amplified signal are N-th order inter-modulation tones of the first amplified signal and the second amplified signal, respectively, the phase shifter sets the phase difference between the first phase and the second phase to be substantially 180°/N.
14. The signal processing apparatus of claim 13 , wherein the baseband input signal comprises an I-channel input signal and a Q-channel input signal, and the phase shifter comprises:
a first transistor, for receiving the I-channel input signal;
a second transistor, coupled to the first transistor, for mirroring the I-channel input signal to generate an I-channel signal of the first baseband signal;
a third transistor, coupled to the first transistor, for mirroring the I-channel input signal to generate a first mirrored signal;
a fourth transistor, for receiving the Q-channel input signal;
a fifth transistor, coupled to the fourth transistor, for mirroring the Q-channel input signal to generate a Q-channel signal of the first baseband signal;
a sixth transistor, coupled to the forth transistor and the third transistor, for mirroring the Q-channel input signal to generate a second mirrored signal, wherein the first mirrored signal is combined with the second mirrored signal for generating one of an I-channel signal and a Q-channel signal of the second baseband signal;
a seventh transistor, coupled to the first transistor, for mirroring the I-channel input signal to generate a third mirrored signal; and
an eighth transistor, coupled to the fourth transistor and the seventh transistor, for mirroring the Q-channel input signal to generate a fourth mirrored signal, wherein the third mirrored signal is combined with the fourth mirrored signal for generating the other of the I-channel signal and the Q-channel signal of the second baseband signal;
wherein aspect ratios of the second transistor, the third transistor, the fifth transistor, and the sixth transistor are substantially equal to 1:A:1:B, aspect ratios of the second transistor, the seventh transistor, the fifth transistor, and the eighth transistor are substantially equal to 1:B:1:A, and B/A is substantially equal to
tan
(
180
°
N
)
.
15. The signal processing apparatus of claim 13 , wherein the baseband input signal comprises an I-channel input signal, a complementary I-channel input signal, a Q-channel input signal, and a complementary Q-channel input signal, and the phase shifter comprises:
a first resistor, having a first resistance, for receiving the Q-channel input signal;
a second resistor, having a second resistance, for receiving the I-channel input signal, wherein a common terminal of the first resistor and the second resistor outputs an I-channel signal of the second baseband signal;
a third resistor, having a third resistance, for receiving the complementary Q-channel input signal;
a fourth resistor, having a fourth resistance, for receiving the complementary I-channel input signal, wherein a common terminal of the third resistor and the fourth resistor outputs an complementary I-channel signal of the second baseband signal;
a fifth resistor, having a fifth resistance, for receiving the complementary I-channel input signal;
a sixth resistor, having a sixth resistance, for receiving the Q-channel input signal, wherein a common terminal of the fifth resistor and the sixth resistor outputs a Q-channel signal of the second baseband signal;
a seventh resistor, having a seventh resistance, for receiving the I-channel input signal; and
an eighth resistor, having an eighth resistance, for receiving the complementary Q-channel input signal, wherein a common terminal of the seventh resistor and the eighth resistor outputs an complementary Q-channel signal of the second baseband signal;
wherein ratios of the second resistance to the first resistance, the fourth resistance to the third resistance, the sixth resistance to the fifth resistance, and the eighth resistance to the seventh resistance are substantially equal to
tan
(
180
°
N
)
.
16. The signal processing apparatus of claim 12 , further comprising:
an adjusting circuit, coupled between the combining circuit and the phase shifter, for detecting the output signal to generate an adjusting signal to the phase shifter for adjusting at least one of the first phase and the second phase.
17. The signal processing apparatus of claim 16 , wherein the adjusting circuit comprises:
a power detector, coupled to the combining circuit, for detecting a power of the output signal to generate a detected value; and
a digital-to-analog converter, coupled between the power detector and the phase shifter, for converting the detected value into the adjusting signal.
18. The signal processing apparatus of claim 16 , wherein when the adjusting circuit detects that a total power of the first specific amplified signal and the second specific amplified signal in the output signal reaches a predetermined power level, the adjusting circuit outputs the adjusting signal to the phase shifter for adjusting at least one of the first phase and the second phase.
19. A signal processing method, comprising:
up-converting a first and second baseband signals into a first and second up-converted signals with a reference clock, wherein a phase difference between the first and second baseband signals substantially equals 180°/N such that N-th order inter-modulation tone in the output signal is reduced; and
combining the first and second up-converted signals to generate an output signal including the reduced N-th order inter-modulation tone and a main signal.
20. The signal processing method of claim 19 , wherein the step of up-converting the first and second baseband signals into the first and second up-converted signals with the reference clock comprises:
transforming the first baseband signal into a first transconducted signal;
mixing the first transconducted signal with the reference clock to generate the first up-converted signal;
transforming the second baseband signal into a second transconducted signal; and
mixing the second transconducted signal with the reference clock to generate the second up-converted signal.
21. The signal processing method of claim 19 , further comprising:
receiving a baseband input signal to generate the first and second baseband signals; and
amplifying the first and second up-converted signals before the first and second up-converted signals being combined.
22. The signal processing method of claim 21 , wherein the first amplified signal comprises a first specific amplified signal, and the second amplified signal comprises a second specific amplified signal; and when the first specific amplified signal and the second specific amplified signal are N-th order inter-modulation tones of the first amplified signal and the second amplified signal, respectively, the step of receiving the baseband input signal to generate the first and second baseband signals comprises:
setting the phase difference between the first and the second baseband signals to be substantially 180°/N.
23. The signal processing method of claim 21 , wherein the baseband input signal comprises an I-channel input signal and a Q-channel input signal.
24. The signal processing method of claim 21 , further comprising:
detecting the output signal to generate an adjusting signal for adjusting at least one phase of the first and second baseband signals.
25. The signal processing method of claim 24 , wherein the step of detecting the output signal to generate the adjusting signal for adjusting at least one phase of the first and second baseband signals comprises:
detecting a power of the output signal to generate a detected value; and
converting the detected value into the adjusting signal;
wherein when detecting that a power corresponding to one of the first specific amplified signal and the second specific amplified signal in the output signal reaches a predetermined power level, outputting the adjusting signal.