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Complex type sigma-delta analog to digital conversion unit and receiverComplex type sigma-delta analog to digital conversion unit and receiver description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060238395, Complex type sigma-delta analog to digital conversion unit and receiver. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-128661, filed on Apr. 26, 2005, 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 complex type sigma-delta analog to digital conversion unit and a receiver having the same. [0004] 2. Description of the Related Art [0005] FIG. 7 is a view showing the configuration of a radio receiver having a real type sigma-delta analog to digital conversion unit described in the following Patent Document 1. A mixer 701a mixes an input signal with a 0.degree. phase shift signal to generate an I signal. A mixer 701b mixes an input signal with a 90.degree. phase shift signal to generate a Q signal. The I signal and Q signal are signals that are orthogonal to each other. A real type sigma-delta analog to digital conversion unit 700a, which includes a subtractor 711, a loop filter 712, an analog to digital (A/D) converter 713, and a digital to analog (D/A) converter 714, converts the I signal into a digital format from an analog format. A real type sigma-delta analog to digital conversion unit 700b, which includes a subtractor 711, a loop filter 712, an analog to digital (A/D) converter 713, and a digital to analog (D/A) converter 714 like the analog to digital conversion device 700a, converts the Q signal into a digital format from an analog format. [0006] FIG. 8 is a view showing the configuration of a radio receiver having a complex type sigma-delta analog to digital conversion unit described in the following Patent Document 2. A mixer 801a mixes an input signal with a 0.degree. phase shift signal to generate an I signal. A mixer 801b mixes an input signal with a 90.degree. phase shift signal to generate a Q signal. The I signal and Q signal are signals that are orthogonal to each other. A complex type sigma-delta analog to digital conversion unit 800 includes subtractors 811a and 811b, loop filters 812a and 812b, analog to digital (A/D) converters 813a and 813b, and digital to analog (D/A) converters 814a and 814b. The output signal of the loop filter 812a is outputted to the loop filter 812b with its positive-negative sign maintained and, and the output signal of the loop filter 812b is outputted to the loop filter 812a with its positive-negative sign inverted. [0007] [Patent document 1] Translated National Publication of Patent Application No. 2003-527795 [0008] [Patent document 2] U.S. Pat. No. 5,764,171 [0009] FIG. 9 is a view showing a quantization noise spectrum of the real type sigma-delta analog to digital conversion unit of FIG. 7. When an input signal is converted into a digital format from an analog format, a quantization noise due to the quantization will be generated. The quantization noise spectrum is symmetrical with respect to the axis of which the frequency is 0 Hz. The frequency range RN of the input signal includes positive and negative low-frequency ranges having a predetermined quantization noise or less. The positive frequency range of the input frequency range RN is a positive signal bandwidth CW. [0010] FIG. 10 is a view showing a quantization noise spectrum of the complex type sigma-delta analog to digital conversion unit of FIG. 8. The difference between the real type and complex type sigma-delta analog to digital conversion units is whether the loop filter has a complex pole or not. In the real type of FIG. 9 the quantization noise spectrum becomes symmetrical with respect to the axis of the frequency is 0 Hz, while in the complex type of FIG. 10 the quantization noise spectrum shifted in the positive direction of the frequency axis can be obtained. In realizing a reduction in the quantization noise in the signal bandwidth CW with the same filter order, the same filter cut-off frequency, the same sampling frequency, and the nearly same power consumption, the complex type of FIG. 10 can reduce it much more as compared with the real type of FIG. 9. [0011] However, in the real type of FIG. 9 the quantization noise level in the negative input frequency range is nearly equal as compared with the one in the positive input frequency range, while in the complex type of FIG. 10 the quantization noise level in the negative input frequency range becomes extremely large as compared with the one in the positive input frequency range and thus the input frequency range RN is restricted to a positive range. SUMMARY OF THE INVENTION [0012] The present invention is intended to provide a complex type sigma-delta analog to digital conversion unit capable of reducing the quantization noise and converting input signals having a positive and negative frequency into a digital format from an analog format, and to provide a receiver. [0013] According to one aspect of the invention, there is provided a complex type sigma-delta analog to digital conversion unit that includes: a first subtractor for carrying out subtraction by inputting a first input signal and a first feedback signal; a first filter for filtering an output signal of the first subtractor; a first analog to digital converter for converting the output signal of the first filter into a digital format from an analog format; a first digital to analog converter which converts an output signal of the first analog to digital converter into an analog format from a digital format and outputs the converted signal to the first subtractor as the first feedback signal; a second subtractor for carrying out subtraction by inputting a second input signal and a second feedback signal, the second input signal being orthogonal to the first input signal; a second filter for filtering an output signal of the second subtractor; a second analog to digital converter for converting the output signal of the second filter into a digital format from an analog format; a second digital to analog converter which converts an output signal of the second analog to digital converter into an analog format from a digital format and outputs the converted signal to the second subtractor as the second feedback signal; a first sign controller which inverts a positive/negative sign of the output signal of the first filter in response to a control signal and outputs it to the second filter; and a second sign controller which inverts a positive/negative sign of the output signal of the second filter in response to the control signal and outputs it to the first filter. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG. 1 is a view showing a configuration example of a radio receiver having a complex type sigma-delta analog to digital conversion unit according to a first embodiment of the invention. [0015] FIG. 2 is a view showing a quantization noise spectrum of the complex type sigma-delta analog to digital conversion unit of FIG. 1. [0016] FIG. 3A and FIG. 3B are views for explaining a low IF (intermediate frequency) system according to this embodiment. [0017] FIG. 4 is a circuit diagram showing a configuration example of a loop filter and a sign controller of FIG. 1 according to a second embodiment of the invention. [0018] FIG. 5 is a circuit diagram showing a configuration example of the loop filter and the sign controller of FIG. 1 according to a third embodiment of the invention. [0019] FIG. 6 is a circuit diagram showing a configuration example of the loop filter and the sign controller of FIG. 1 according to a fourth embodiment of the invention. [0020] FIG. 7 is a view showing the configuration of a radio receiver having a real type sigma-delta analog to digital conversion unit of Patent Document 1. Continue reading about Complex type sigma-delta analog to digital conversion unit and receiver... Full patent description for Complex type sigma-delta analog to digital conversion unit and receiver Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Complex type sigma-delta analog to digital conversion unit and receiver 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. 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