LO Phase Rotator Calibration for Harmonic Reject Mixers
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Solution Overview
Problem
Harmonic rejection in RF mixers is limited by phase and gain mismatches in the local oscillator (LO) path, leading to suboptimal rejection of odd harmonics, which can be exacerbated by manufacturing variations and non-ideal LO generation techniques, restricting the performance of mixers in wide-band applications.
Innovation Solution
Incorporating a phase rotator in the LO path with digital control to provide phase and gain adjustments, allowing for precise 45 and 90-degree phase shifts and amplitude scaling, which compensates for mismatches and enhances harmonic rejection by creating a 3-bit quantized sinusoidal signal, effectively canceling 3rd and 5th harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large local oscillator signal is used to drive switching mixers for quick switching, then switching speed and current commutation improve, but odd harmonic content increases causing stray signals at the mixer output
Solution Approach 1:
The single mixer is divided into three parallel mixers, each processing a different phase-shifted version of the LO signal. This segmentation allows the harmful odd harmonics to be canceled through destructive interference when the outputs are combined, while preserving the beneficial quick switching behavior of each individual mixer.
Solution Approach 2:
The patent converts the harmful odd harmonic content generated by the compressed LO signal into a beneficial cancellation mechanism. By introducing specific phase shifts (0, 45, and 90 degrees) to three parallel LO signals and combining them through mixers, the odd harmonics destructively interfere and cancel each other out, transforming the harmful compression artifacts into improved spectral purity.
2Object-generated harmful factors
If phase shifts are introduced to create quantized sinusoidal signal for harmonic rejection, then 3rd and 5th harmonics are canceled, but phase and gain mismatches reduce rejection performance
Solution Approach 1:
The patent implements self-calibration circuitry that automatically detects and corrects phase and gain mismatches in the LO distribution network. The system uses the known structure of the quantized sinusoidal signal to identify mismatch conditions and adjusts the phase and gain of individual LO paths to optimize harmonic rejection, eliminating the need for external calibration equipment or manual adjustment.
Solution Approach 2:
The patent employs feedback mechanisms where the mixer outputs are monitored and used to adjust the LO signal parameters. By detecting the presence of residual harmonics and feeding this information back to the LO distribution network, the system dynamically adjusts phase and gain settings to maintain optimal harmonic rejection despite manufacturing variations or environmental changes.
3Object-generated harmful factors
If three parallel mixers are used with phase shifted LO signals, then harmonic rejection improves, but device complexity increases
Solution Approach 1:
The patent merges three parallel mixer paths into a single integrated harmonic rejection mixer structure. By combining the LO distribution network, three mixer cores, and output combining circuitry into one unified device, the patent achieves improved harmonic rejection while minimizing the increase in device complexity through shared components and integrated design.
Solution Approach 2:
The patent designs the phase rotator and LO distribution network to serve multiple functions simultaneously: generating the required phase shifts for harmonic rejection, providing calibration signals for mismatch compensation, and distributing LO signals to all three mixer paths. This multi-functionality reduces the overall device complexity by eliminating the need for separate circuits for each function.
Data Source
AI summary
A harmonic rejection mixer having a phase rotator fed by a local oscillator signal. The local oscillator signal has a reference frequency. The phase rotator produces a plurality of output signals, each one of the signals having a common frequency related to the reference frequency and having different relative phase shifts. A plurality of mixer sections, each one of the sections being fed an input signal and a corresponding one of the plurality of output signals mixes the local oscillator signal with the corresponding one of the plurality of output signals fed thereto. A combiner combines the mixer signal from the plurality of mixer sections into a composite output signal. A detector detects energy in a harmonic of the composite signal and for adjusting the output signal of the phase rotator to reduce the selected harmonic of the composite signal.