Mixer IIP2 Calibration Using Single-Tone Reverse Feedthrough
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Solution Overview
Problem
Current mixer calibration techniques are inefficient in reducing second-order intermodulation distortion (IMD2) and require extensive calibration time, often involving multiple RF tones and port switching, which increases cost and circuit area.
Innovation Solution
A method and apparatus for mixer IIP2 calibration using a single baseband tone to generate a differential tone, and adjusting the mixer to minimize its power, or downconverting RF signals and amplifying IMD2 products to adjust the mixer, thereby reducing calibration time and circuit footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple RF tones and port switching are used for mixer calibration, then calibration accuracy is improved, but calibration time and circuit area increase
Solution Approach 1:
The patent extracts the essential calibration function by using only a single RF tone instead of multiple tones, and by eliminating port switching operations. This extraction maintains the core capability to measure and adjust mixer linearity while removing the time-consuming elements of the traditional calibration process.
Solution Approach 2:
The patent inverts the traditional calibration approach by using reverse feedthrough measurement - instead of measuring forward transmission, it measures the reverse feedthrough signal from the LO port to the RF port. This inversion enables calibration without port switching and reduces the number of required measurement points.
2Measurement precision
If multiple RF tones and port switching are used for mixer calibration, then calibration accuracy is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the essential calibration components by eliminating the need for multiple RF tone generators and port switching mechanisms. The solution uses a single RF tone and direct feedthrough measurement paths, significantly reducing the circuit area required for calibration functionality.
Solution Approach 2:
The patent makes existing circuit components multi-functional by using the same RF path and measurement infrastructure for both forward and reverse calibration measurements. The reverse feedthrough measurement utilizes existing LO and RF ports without requiring additional dedicated calibration ports or switching infrastructure.
3Productivity
If reverse feedthrough amplification is used, then calibration speed is improved, but circuit area increases
Solution Approach 1:
The patent merges the calibration function with the existing signal processing chain by incorporating the amplification and measurement of reverse feedthrough signals through the same RF path and baseband processing infrastructure already present in the receiver, rather than adding completely separate calibration hardware.
Solution Approach 2:
The calibration system uses the receiver's own existing components - including amplifiers, mixers, and baseband processing - to perform the calibration measurement. The reverse feedthrough signal is amplified and processed through the normal signal path, allowing the system to calibrate itself using its existing infrastructure.
Data Source
AI summary
Methods and apparatus for calibration of a second-order input intercept point (IIP2) of a mixer, such as a mixer in a wireless receive chain. One example circuit for mixer IIP2 calibration generally includes a first receive chain comprising a first mixer and a single tone generator having an output coupled to an input of the first mixer and configured to generate a calibration signal having a single baseband tone. One example method of mixer IIP2 calibration generally includes generating a calibration signal comprising a single baseband tone, applying the calibration signal to an input of a mixer, such that the mixer generates a differential tone at an output of the mixer, and adjusting the mixer to minimize a power of the differential tone at the output of the mixer.