Phase correcting apparatus and distortion compensating apparatus for radio transmitter

• US 8,494,069 B2
• Filed: 03/10/2010
• Issued: 07/23/2013
• Est. Priority Date: 03/12/2009
• Status: Expired due to Fees

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Miyashita, Takumi
• Primary Examiner(s): Nguyen, Leon-Viet
• Assistant Examiner(s): Hassan, Sarah
• Application Number:
  US12/721,138
• Publication Number:
  US 20100232481A1
• Time in Patent Office: 1,231 Days
• Field of Search: 375/222, 375/261, 356/464
• US Class Current: 375/261
• 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, the phase correcting apparatus comprising:

a demodulator which extracts a feedback signal from a part of a first baseband signal, and extracts a second baseband signal from the feedback signal by a first carrier wave 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, by using the phase difference as a target phase correction amount, 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 comprises

a first analog processing circuit which obtains a first analog signal by multiplying an I component of the first baseband signal and a Q component of the second baseband signal,

a second analog processing circuit which obtains a second analog signal by multiplying a Q component of the first baseband signal and an I component of the second baseband signal, and

a digital processing circuit which converts a difference between the first analog signal and the second analog signal into digital data, and which detects the phase difference based on the converted digital data.

2. The phase correcting apparatus for the radio transmitter according to claim 1, wherein the digital processing circuit comprises:

a sigma-delta type analog-to-digital converter which converts the difference between the first analog signal and the second analog

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. The phase correcting apparatus for the radio transmitter according to claim 1, further comprising:

a first low-pass filter located at a first node at 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 second low-pass filter having a filter characteristic which is different to that of the first low-pass filter, wherein

the demodulator includes a first demodulator and a second demodulator,

the first low-pass filter is arranged to filter the second baseband signal from the first demodulator,

the second low-pass filter is arranged to filter the second baseband signal from the second demodulator, and

the phase correcting apparatus is arranged such that 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 the phase difference detector.

4. The phase correcting apparatus for the radio transmitter according to claim 3, wherein

the difference signal is extracted by a source follower circuit comprising a transistor having a gate terminal connected to the first node and a drain terminal connected to power-supply voltage.