Harmonic Suppression Mixer With Multiphase LO Weighted Summing
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Solution Overview
Problem
Existing radio frequency mixers in tuners suffer from harmonic conversion issues, leading to interference from unwanted frequencies, particularly in broadband systems like television, where harmonic interferers can disrupt the tuned channel.
Innovation Solution
A harmonic suppression mixer is developed using a plurality of switching mixers driven by staggered digital signals, with weighted summing of outputs to suppress higher frequency signals, and a precision multiphase LO generator to produce staggered LO signals, effectively reducing LO leakage and non-ideal characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If switching mixers are used to reduce in-band noise, then noise performance is improved, but harmonic conversion gain increases causing interference from unwanted frequencies
Solution Approach 1:
The patent divides a single mixer function into multiple switching mixers (first, second, third, and fourth mixers) that process signals through separate paths. Each mixer handles specific frequency conversions, and their outputs are combined to achieve the desired frequency translation while canceling harmonic interference through coherent combining techniques.
Solution Approach 2:
The patent combines the outputs of multiple switching mixers to achieve both noise reduction and harmonic suppression. By coherently combining signals from parallel mixer paths with proper phase and amplitude relationships, the desired signal is reinforced while harmonic components cancel each other out, resolving the contradiction between low noise and low harmonic gain.
2Object-generated harmful factors
If multiple mixers are used to suppress harmonic interference, then harmonic conversion is reduced, but device complexity increases
Solution Approach 1:
The multiple mixers in the patent serve dual functions: they perform frequency conversion (standard mixer function) and simultaneously provide harmonic suppression through their coordinated operation. This multi-functionality reduces the need for additional dedicated harmonic filtering components, thereby limiting the increase in overall device complexity while achieving harmonic interference suppression.
3Object-generated harmful factors
If staggered digital signals are used to drive mixers, then harmonic suppression is improved, but signal processing complexity increases
Solution Approach 1:
The patent employs staggered digital signals with specific periodic timing relationships to drive the multiple mixers. These periodic control signals are synchronized to create constructive interference for the desired frequency component and destructive interference for harmonic components. The periodic nature of these control signals simplifies the processing complexity compared to arbitrary waveforms, as they can be generated using standard clocking and phase-shifting circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses harmonic interference, improving signal quality by averaging non-ideal mixer characteristics and reducing deterministic errors, while being suitable for wide tuning ranges and adaptable configurations.
Implementation Method 1
A harmonic suppression mixer is developed using a plurality of switching mixers driven by staggered digital signals, with weighted summing of outputs to suppress higher frequency signals
Data Source
AI summary
A harmonic suppression mixer for down converting an RF signal to a complex I and Q baseband signal that uses a plurality of switching mixers each with a gain stage to produce a sinusoidal weighted sum of the mixer outputs. Odd harmonics output by each switching mixer is suppressed in the composite signal. A low skew local oscillator (LO) clock generator creates multiple LO phases and drives the mixers. The mixer can be used in low noise direct conversion RF tuners. The mixer is configurable by programming gain stage coefficient values to achieve a variable number of effective mixers used in combination. At low tuning frequencies, all available mixers are programmed with unique coefficients and driven by different LO clock phases to achieve maximum harmonic suppression. At high tuning frequencies, some mixers are paralleled and duplicate coefficients are programmed or mixers are disabled to reduce the number of effective mixers.