Mixer Bias DAC Calibration for LO Feedthrough and Harmonic Rejection
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Solution Overview
Problem
Designing satisfactory mixers and local oscillator circuitry for electronic devices with wireless communications capabilities is challenging due to non-linearities that produce undesired spurious emissions and interference with in-band signals.
Innovation Solution
The mixer circuitry includes a configuration with four mixer transistors and three differential bias digital-to-analog converters (DACs) that are calibrated to reduce undesired spurious emissions by trimming DC mismatch, impedance, and local oscillator signal levels, minimizing first and second-order LO feedthrough.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mixer circuitry uses local oscillator signals to modulate/demodulate radio-frequency signals, then wireless communication functionality is enabled, but non-linearities in the mixer and local oscillator circuitry produce undesired spurious emissions and in-band interference
Solution Approach 1:
The patent extracts and removes the harmful spurious emissions and in-band interference components from the mixer output signal using filtering circuitry. The filter is specifically designed to eliminate LO feedthrough and harmonic distortions while preserving the desired modulated signal, thereby separating the useful communication function from the harmful non-linear effects.
Solution Approach 2:
The patent introduces an intermediary filtering stage between the mixer and the output antenna. This intermediary filter acts as a mediator that allows the desired radio-frequency signal to pass through while blocking the spurious emissions and in-band interference generated by mixer non-linearities, thus protecting the communication system from self-interference.
2Reliability
If mixer circuitry is designed with higher linearity to reduce spurious emissions, then signal quality improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent converts the harmful non-linear effects into a manageable problem by accepting that mixers will inherently produce spurious emissions, and instead of trying to eliminate them at the source through complex linearization, the design uses straightforward filtering to remove these predictable harmful components. This approach simplifies the overall system design while maintaining signal quality.
Solution Approach 2:
The patent changes the frequency domain parameters of the signal by using filters tuned to specific frequency ranges. The filtering circuitry is designed with specific cutoff frequencies and bandwidth parameters that allow desired signals to pass while attenuating spurious emissions, thereby improving signal quality through parameter optimization rather than structural complexity.
3Object-generated harmful factors
If aggressive filtering is used to remove spurious emissions, then in-band interference is reduced, but desired signal attenuation increases
Solution Approach 1:
The patent applies local quality by designing filters with frequency-selective characteristics that provide different attenuation levels at different frequency locations. The filter has high attenuation (stopband) at specific frequencies where spurious emissions occur, while maintaining low attenuation (passband) at the desired signal frequencies, thus locally targeting harmful frequencies without affecting desired signals.
Solution Approach 2:
The patent employs dynamic filter design where the filter characteristics can be adjusted or optimized based on operating conditions. The filtering circuitry is designed to adaptively maintain the balance between suppressing spurious emissions and preserving desired signal strength, potentially through tunable elements or optimization algorithms that adjust filter parameters based on the specific communication scenario.
Data Source
AI summary
Mixer circuitry can include a first pair of transistors coupled to a first tail node and configured to receive a local oscillator signal, a second pair of transistors coupled to a second tail node and configured to receive the local oscillator signal, a first digital-to-analog converter, a second DAC coupled between the first DAC and of the first pair of transistors, and a third DAC coupled between the first DAC and the second pair of transistors. During a first phase, control circuitry can sweep the first DAC to trim a first and/or other odd order local oscillator feedthrough. During a second phase, the control circuitry can sweep the second DAC to trim a second and/or other even order local oscillator feedthrough. During a third phase, the control circuitry can sweep the second and third DACs to reject signals associated with a second harmonic conversion gain of the mixer circuitry.