Skewed π/2 Phase Detector for 45° LO Calibration
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Solution Overview
Problem
The increasing self-generated interference in wireless communication devices, particularly in handheld devices, due to the coexistence of various communication interfaces, poses challenges for harmonic rejection mixers, which require accurate phase differences between local oscillator waveforms to maintain effective harmonic rejection properties.
Innovation Solution
A background calibration scheme for 45° phase difference LO signals is introduced, utilizing a modified symmetric π/2 phase-detector with additional current sources for skewing and load balancing, allowing for fractional phase-difference detection and minimizing phase errors, thereby enhancing harmonic rejection and reducing filtering requirements for coexistence with cellular and mobile TV receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive HR mixers are used to improve linearity and reduce 1/f noise, then measurement precision is improved, but device complexity increases due to implementation difficulty
Solution Approach 1:
The passive HR mixer is divided into separate functional blocks: a quadrature signal generator that produces precise 90-degree phase-shifted LO signals, and the mixing stage. The phase detector is segmented into multiple taps that sample different phases. This segmentation allows each block to be optimized independently, achieving high linearity and low noise while managing complexity through modular design.
Solution Approach 2:
The quadrature signal generator performs preliminary phase shifting and signal preparation before the mixing operation. By pre-generating accurately phase-shifted LO signals through a dedicated quadrature generator with phase detector and feedback loop, the system ensures precise phase relationships are established beforehand, enabling the passive mixer to achieve optimal linearity and noise performance without requiring complex real-time adjustments.
2Adaptability or versatility
If multiple communication interfaces coexist in handheld devices, then adaptability is improved, but self-generated interference increases
Solution Approach 1:
The system converts potential interference from coexisting communication interfaces into useful information by using a phase detector to monitor phase relationships between different LO signals. The phase detector output provides feedback that allows the system to adjust and synchronize phases, transforming what would be harmful interference into a mechanism for achieving precise phase control and enabling harmonic rejection that actually improves coexistence.
Solution Approach 2:
A feedback loop is implemented where the phase detector continuously monitors the phase relationship between LO signals from different communication interfaces. The phase detector output is fed back to adjust the phase shifters or LO generation, ensuring that phase relationships are maintained at optimal values for harmonic rejection. This feedback mechanism enables multiple interfaces to coexist by actively managing and correcting phase-related interference in real-time.
3Loss of energy
If harmonic rejection properties are improved by accurate phase control, then filtering requirements are reduced, but phase detection precision must be increased
Solution Approach 1:
The phase detector uses multiple taps sampled at different phases (0, 90, 180, 270 degrees) rather than a single phase measurement. By sampling in the phase dimension and combining these measurements, the system achieves high phase detection accuracy. The multiple taps provide redundant information that can be processed to determine phase relationships with high precision, enabling accurate harmonic rejection control without requiring oversampling at a single point.
Data Source
AI summary
A basic symmetric Π/2 phase-detector receives four control signals that control a differential current at the detector's output. Each respective control signal is a linear combination of a respective pair of signals chosen from a first input signal, its logic complement, a second input signal and the logic complement of the latter. Operation is based on time-averaging the differential current, the result being zero at a phase difference of Π/2. By means of adding one or more additional current sources to the output, controlled by one or more of the control signals, the basic operation is skewed. The time-averaged output current is now made zero only at a value of the phase difference different from Π/2. In an embodiment with uniform current sources and resistors, the modified detector is configured for a phase difference of Π/2N .