PHASE CORRECTING APPARATUS AND DISTORTION COMPENSATING APPARATUS FOR RADIO TRANSMITTER

• US 20100232481A1
• Filed: 03/10/2010
• Published: 09/16/2010
• Est. Priority Date: 03/12/2009
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Miyashita, Takumi
• Granted Patent: US 8,494,069 B2
• Time in Patent Office: Days
• US Class Current: 375/219
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 2200/336 A I/Q, i.e. phase quadrature, modulator or demodulator being used in an amplifying circuit
• CPC Class Codes: H03F 2200/57 Separate feedback of real and complex signals being present
• CPC Class Codes: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

A phase correcting apparatus, for a radio transmitter which obtains a first radio signal (RS1) based on a first baseband signal (BB1), includes a demodulator which demodulates a feedback signal from which a part of RS1 is extracted by a first carrier signal (CS1) and which generates a second baseband signal (BB2), a modulator which modulates a difference signal between BB1 and BB2 by a second carrier signal (CS2) and which outputs a second radio signal (RS2), a power amplifier which amplifies RS2 to obtain RS1, a detector which detects a phase difference between BB1 and BB2, and a phase rotator which rotates any phase of BB1, BB2, CS1, or CS2 as a target phase correction amount, wherein the detector converts a desired analog signal obtained by multiplying BB1 and BB2 into a digital signal, and which detects the phase difference based on digital data.

Claims

1. A phase correcting apparatus for a radio transmitter which obtains a first radio signal based on a first baseband signal, the phase correcting apparatus comprising:

a demodulator which demodulates a feedback signal from which a part of the first radio signal is extracted by a first carrier wave signal and which generates a second baseband signal,

a modulator which modulates a difference signal between the first baseband signal and the second baseband signal by a second carrier wave signal and which outputs a second radio signal,

a power amplifier which amplifies the second radio signal to obtain the first radio signal,

a phase difference detector which detects a phase difference between the first baseband signal and the second baseband signal, and

a phase rotator which rotates any phase of the first baseband signal, the second baseband signal, the first carrier wave signal, or the second carrier wave signal as a target phase correction amount,

wherein the phase difference detector converts a desired analog signal which is obtained by multiplying the first baseband signal and the second baseband signal into a digital signal, and which detects the phase difference based on digital data.

2. The phase correcting apparatus for the radio transmitter according to claim 1, wherein the phase difference detector comprises:

a sigma-delta type analog-to-digital converter which converts the desired analog signal into the digital data,

a counter which multiplies an output bit of the sigma-delta type analog-to-digital converter, and

a memory which refers to a count value of the counter as an address for a trigonometric function value of a phase angle corresponding to the target phase correction amount.

3. A distortion compensating apparatus for a radio transmitter which obtains a first radio signal based on a first baseband signal, wherein the distortion compensating apparatus comprises:

a demodulator which demodulates a feedback signal from which a part of the first baseband signal is extracted by a first carrier wave signal and which generates a second baseband signal,

a modulator which modulates a difference signal between the first baseband signal and the second baseband signal by a second carrier wave signal and outputs a second radio signal, and

a power amplifier which amplifies the second radio signal to obtain the first radio signal,

wherein, in a first node in which a first signal line for transmitting the first baseband signal is connected to a second signal line for transmitting the second baseband signal, a first low-pass filter as a desired characteristic is set.

4. The distortion compensating apparatus for the radio transmitter according to claim 3, wherein the distortion compensating apparatus comprises a first demodulator and a second demodulator which generate a second baseband signal,

wherein the second baseband signal from the first demodulator is sent to the second signal line, and the second baseband signal from the second demodulator is sent to a phase difference detector,

and wherein a second low-pass filter with a characteristic different from that of the first low-pass filter is set with respect to the second baseband signal from the second demodulator.

5. The distortion compensating apparatus for the radio transmitter according to claim 3, wherein the difference signal is extracted by a source follower circuit of a transistor having a gate terminal connected to the first node and a drain terminal connected to power-supply voltage.