Distortion compensating circuit

• US 5,404,378 A
• Filed: 04/04/1994
• Issued: 04/04/1995
• Est. Priority Date: 04/20/1993
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Kimura, Kazuo
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): GHEBRETINSAE, TEMESGHEN
• Application Number:
  US08/222,530
• Time in Patent Office: 365 Days
• Field of Search: 375/60, 375/39, 332/123, 332/124, 332/159, 330/149, 328/162, 328/163, 455/63, 455/126, 307/491
• US Class Current: 375/296
• CPC Class Codes: H03C 3/08 Modifications of modulator to linearise modulation, e.g. by feedback, and clearly applicable to more than one type of modulator
• CPC Class Codes: H03D 7/168 using a feedback loop containing mixers or demodulators
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 2200/57 Separate feedback of real and complex signals being present
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

In a distortion compensating circuit, an initial value sufficient to provide a distortion compensating effect is previously set in a memory storage for storing distortion compensating data, whereby the convergence time of the distortion compensating effect is shortened.

Claims

1. A distortion compensating circuit for compensating a nonlinear distortion generated in an amplifier for amplifying a signal modulated by a base band signal, comprising:

distortion correcting means that is intermittently operated, including a memory storage for storing distortion compensating data for compensating the nonlinear distortion in the output of said amplifier, and a subtracter for subtracting said distortion compensating data in said memory storage from said base band signal to output a corrected base band signal;

a modulator for modulating a carrier signal by said corrected base band signal outputted from said distortion correcting means to output a modulated signal to said amplifier;

a demodulator for demodulating a part of the signal outputted from said modulator;

comparing means for comparing the demodulated signal outputted from said demodulator with said base band signal to output said distortion compensating data to said memory storage; and

initial value setting means for setting an initial value of said distortion compensating data in said memory storage, said initial value being sufficient to compensate the nonlinear distortion.

2. A distortion compensating circuit as claimed in claim 1, wherein said initial value is the distortion compensating data generated at the end of the previous operating period of said distortion correcting means.

3. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by a temperature of said amplifier.

4. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by an amplification degree of said amplifier.

5. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by an output level of said amplifier.

6. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by a power supply voltage of said amplifier.

7. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by an output impedance of said amplifier.

8. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by an input impedance of said amplifier.

9. A distortion compensating circuit as claimed in claim 1, wherein said initial value is determined by any combination of a temperature, an amplification degree, an output level, a power supply voltage, an output impedance, and an input impedance of said amplifier.