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Radio receiver and radio signal processing methodRelated Patent Categories: Telecommunications, Receiver Or Analog Modulated Signal Frequency Converter, Local Control Of Receiver Operation, Gain Control, Automatic, Automatic Gain Control Signal Derived From Information SignalRadio receiver and radio signal processing method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070224960, Radio receiver and radio signal processing method. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a Divisional of and claims the benefit of priority under 35 USC .sctn. 120 from U.S. Ser. No. 10/819,288, filed Apr. 7, 2004, claims the benefit of priority under 35 U.S.C. .sctn.119 from the prior Japanese Patent Application No. 2003-122316, filed on Apr. 25, 2003, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a radio receiver and a radio signal processing method. [0004] 2. Related Background Art [0005] In recent years, radio communication devices have widely spread. As a result, it is increasingly demanded to reduce the number of components and the manufacture cost for a radio circuit and manufacture the radio circuit as a monolithic IC. In order to cope with this demand, the direct conversion scheme is adopted for the radio circuits. [0006] FIG. 8 is a block diagram of a conventional receiver adopting the direct conversion scheme. An antenna 10 receives an RF (Radio Frequency) signal, and an LNA (Low Noise Amplifier) 20 amplifies this RF signal. A quadrature demodulator 30 multiplies the amplified RF signal by an LO (Local Oscillator) signal supplied from a local oscillator (not illustrated). As a result, the RF signal is directly converted to a baseband signal. An LPF (Low Pass Filer) 40 conducts waveform shaping on the baseband signal, and a VGA (Variable Gain Amplifier) 50 amplifies this baseband signal. In addition, a demodulator 70 demodulates this baseband signal to a digital signal. In this way, the receiver using the direct conversion scheme converts the RF signal to a digital signal, and then demodulates it by using digital signal processing. [0007] The baseband signal amplified by the VGA 50 is input not only to the demodulator 70 but also to a gain controller 60 and a DC offset canceller 94. In the gain controller 60, a signal strength detector 80 measures the strength of the baseband signal. A gain selector 90 decides whether to switch the gain of the LNA 20 and the gain of the VGA 50 on the basis of the measured value of the baseband signal. A gain control signal generator 92 outputs a gain control signal to the LNA 20 and the VGA 50 to switch the gain in accordance with the decision made by the gain selector 90. In this way, the gain controller 60 effects feedback control on the strength of the baseband signal. [0008] The DC (Direct Current) offset canceller 94 removes a DC offset component from the baseband signal amplified by the VGA 50, and feeds back this to the VGA 50. By the way, problems concerning the DC offset component are described in "Research development tendency of mixer for direct conversion receiver("Mission Impossible ? A Review of Mixers for Direct-Conversion Receivers")" written by Hiroshi Tanimoto, The Transactions of the Institute of Electronics, Information, and Communication Engineers, section C, Vol. J84-C, No. 5, pp. 337-348, May 2001. [0009] FIGS. 9A and 9B are graphs showing gains of the LNA 20 and the VGA 50, respectively. FIG. 9C is a graph showing a transient response component of a DC offset in the output of the VGA 50. The gains of the LNA 20 and the VGA 50 are simultaneously switched. [0010] When the LNA 20 is switched from a high gain to a low gain at a point t.sub.1 in time, the VGA 50 is switched simultaneously from a low gain to a high gain. In some cases, therefore, DC offsets of both the LNA 20 and the VGA 50 overlap eachother, and a very large transient response component occurs, resulting in a degraded reception performance. This is because the LNA 20 is disposed in a stage in the radio circuit preceding the VGA 50, and consequently the transient response component of the DC offset generated in the LNA 20 is amplified by the high gain obtained after the change in the VGA 50. SUMMARY OF THE INVENTION [0011] An advantage of an aspect of the present invention is to provide a radio receiver of direct conversion scheme in which degradation of the reception performance caused by the transient response component of the DC offset is suppressed. [0012] A radio receiver of an embodiment accordance with the instant invention comprises a first amplifier to amplify a received radio signal; a demodulation circuit line comprising a quadrature demodulator to demodulate the radio signal amplified by said first amplifier and to generate a baseband signal, a second amplifier to amplify the baseband signal, and a demodulator to demodulate the baseband signal amplified by said second amplifier; and a gain controller to control timing of a change in a gain of said second amplifier, in case that the gain of said first amplifier and the gain of said second amplifier are changed, on the basis of a gain of said first amplifier before and after the change. [0013] A radio receiver of another embodiment accordance with the instant invention comprises a radio receiver comprising: a first amplifier to amplify a received radio signal; a quadrature demodulator to demodulate the radio signal amplified by said first amplifier and to generate a baseband signal; a second amplifier to amplify, after changing a gain of said first amplifier, the baseband signal with a gain based on a gain of said first amplifier obtained before and after the change; and a demodulator to demodulate the baseband signal amplified by said second amplifier. [0014] A radio receiver of further embodiment accordance with the instant invention comprises a first amplifier to amplify a received radio signal; a quadrature demodulator to demodulate the radio signal amplified by said first amplifier and to generate a baseband signal; a second amplifier to amplify the baseband signal; a demodulator to demodulate the baseband signal amplified by said second amplifier; and a gain controller to delay timing of a change in a gain of said second amplifier as compared with timing of a change in a gain of said first amplifier, in case that the gain of said first amplifier is changed from a high gain to a low gain and the gain of said second amplifier is changed from a low gain to a high gain. [0015] A radio signal processing method of an embodiment accordance with the instant invention comprises: receiving a radio signal; amplifying the radio signal; demodulating the amplified radio signal to a baseband signal; amplifying the baseband signal; demodulating the amplified baseband signal; determining timing of a change in a gain of said first amplifier and a gain of said second amplifier, in case that the gain of said first amplifier and the gain of said second amplifier are changed, on the basis of the gain of said first amplifier obtained before and after the change; and changing the gain of said first amplifier and the gain of said second amplifier in accordance with the determined timing. DESCRIPTION OF THE DRAWINGS [0016] FIG. 1 is a block diagram showing an embodiment according to the present invention; [0017] FIG. 2 is a block diagram showing a concrete example of a change timing controller 196; [0018] FIGS. 3A to 3F are time charts showing gains of the LNA 120 and VGA 150, and signal strength of a baseband signal; [0019] FIGS. 4A to 4H are time charts showing gains of the LNA 120 and VGA 150 during phasing and signal strengths of a received signal and a baseband signal; [0020] FIG. 5 is a flow diagram showing operation of a radio receiver in an embodiment; Continue reading about Radio receiver and radio signal processing method... Full patent description for Radio receiver and radio signal processing method Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Radio receiver and radio signal processing method patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Radio receiver and radio signal processing method or other areas of interest. ### Previous Patent Application: Adjustable automatic gain control Next Patent Application: Receiver circuit Industry Class: Telecommunications ### FreshPatents.com Support Thank you for viewing the Radio receiver and radio signal processing method patent info. 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