Patent Application
20110007848
The present invention relates generally to receivers and more to calibrating the mismatch between I data and Q data in such receivers.
Receivers are utilized in a variety of environments. They are utilized, for example, in RF transceivers in various applications. In a receiver, during normal operating mode, a radio-frequency (RF) input signal amplified by a low-noise amplifier (LNA) is downconverted to in-phase (I) and quadrature-phase (Q) baseband signals by an I mixer and a Q mixer respectively. The local oscillator (LO) ports of the I mixer and the Q mixer are driven by an I local-oscillator (LO) signal and Q LO signal, respectively. The I mixer LO signal and Q mixer LO signal are orthogonal (90 degree phase shift) to each other. An I baseband signal and Q baseband signal are then amplified and filtered by baseband filters and variable-gain amplifiers (VGA) before they are digitized by a pair of analog-to-digital converters (ADCs). Due to random process variation, the I path and Q path are not perfectly matched. This results in phase and amplitude mismatches in the I data and Q data, degrading the reception quality and hence increasing the bit-error rate in a digital communication system.
Accordingly, what is desired is a system and method to address the IQ mismatch issues The system and method should be cost effective, easily implemented and adaptable to existing receivers. The present invention addresses such a need.
A method and system for calibrating the mismatch between I data and Q data of a receiver is disclosed. The receiver includes an amplifier, first and second mixers coupled to the amplifier, an oscillator for driving the first and second mixers; and first and second filter coupled to the first and second mixers. The method and system comprise turning off the amplifier; and injecting a signal into the first and second mixers. The method and system also includes measuring the amplitude and phase information of the I and Q data from the first and second mixers based upon the injected signal to provide mismatch information and utilizing the mismatch information to compensate the I data and the Q data during normal operating mode.
In a method and system in accordance with an embodiment, the IQ mismatch of a receiver can be measured and compensated. This allows, for example, for direct-conversion architecture, which is known to have IQ mismatch problem, to be utilized in an effective manner. Furthermore, if this calibration method is applied to other receiver architectures, the yield loss due to IQ mismatch can be minimized.
The accompanying drawings illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. One skilled in the art will recognize that the particular embodiments illustrated in the drawings are merely exemplary, and are not intended to limit the scope of the present invention.
The present invention relates generally to receivers and more to calibrating the mismatch between I data and Q data in such receivers. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
As before mentioned, in normal operating mode, the radio-frequency (RF) input signal 102 amplified by the low-noise amplifier (LNA) 104 is downconverted to in-phase (I) 114 and quadrature-phase (Q) 116 baseband signals by the I mixer 106 and Q mixer 108 respectively. The LO ports of the I mixer 106 and Q mixer 108 are driven by the I local-oscillator (LO) signal 110 and Q local-oscillator (LO) signal 112, respectively. The I LO signal 110 and Q LO signal 112 are orthogonal (90 degree phase shift) with each other. The I baseband signal 114 and Q baseband signal 116 are then amplified and filtered by the baseband filters and variable-gain amplifiers (VGAs) 118 and 120 before they are digitized by a pair of analog-to-digital converters (ADCs) 122 and 124. Due to random process variation, the I path and Q path are not perfectly matched. This results in phase and amplitude mismatches in the I data 128 and Q data 130, degrading the reception quality and hence increasing the bit error rate in the receiver 100 of a digital communication system.
To solve this IQ mismatch problem, the IQ amplitude and phase mismatch needs to be measured and compensated. In an embodiment to measure this IQ mismatch, a single-tone generator 129 is utilized in the receiver during calibration mode. In calibration mode, the LNA 104 is turned off and the single-tone generator 129 is used to inject a sinusoidal signal, the frequency of which is different from the LO frequency, to the input ports of the I mixer 106 and the Q mixers 108. In an ideal situation where the I and Q signal paths are perfectly matched, the resulting sinusoidal I and Q data have exactly the same amplitude and 90-degree phase difference. In a practical situation, however, the mismatches in the I and Q signal paths cause the amplitude and phase of the I data and Q data to be different. This amplitude and phase mismatch information can be measured by the digital circuits 126 during the calibration mode and then can be used to compensate the I data and Q data during the normal operating mode.
Besides the particular implementation described above, there are several variations to this technique. Although
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.
