Multi-Core Mixer Layout for Local Oscillator Leakage Cancellation
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Solution Overview
Problem
Mixers, such as diode ring and FET ring mixers, face challenges in reducing local oscillator (LO) leakage, which corrupts signal purity due to physical layout mismatches and component interferences, making it difficult to suppress LO leakage effectively across various frequency bands.
Innovation Solution
A multi-core mixer configuration with two double-balanced mixer cores, where each core receives a local oscillator signal 180° out of phase with the other, and input signals 180° out of phase, allowing the outputs to be combined to cancel LO leakage, thereby compensating for layout mismatches and improving signal purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single double-balanced mixer core is used, then the device complexity is low, but local oscillator leakage corrupts signal purity
Solution Approach 1:
The mixer is divided into multiple double-balanced mixer cores (first, second, third, and fourth cores) that process signals independently and then combine their outputs. Each core handles a portion of the mixing function, and their combined output achieves superior LO leakage cancellation compared to a single core, directly resolving the contradiction between complexity and harmful factor reduction.
Solution Approach 2:
The outputs of multiple double-balanced mixer cores are combined to produce the final output signal. This merging of multiple processing paths enables the system to cancel LO leakage through constructive and destructive interference of the leaked signals from different cores, achieving better signal purity while distributing the complexity across multiple functional units.
2Object-affected harmful factors
If RF filtering is applied to reduce LO leakage, then signal purity improves, but the circuit complexity and cost increase
Solution Approach 1:
The patent converts the harmful LO leakage signals into a beneficial cancellation mechanism. By designing the mixer cores to produce LO leakage signals with specific phase relationships, the leaked signals from different cores interfere destructively at the output, transforming what would be harmful interference into a useful cancellation effect that reduces the need for additional filtering components.
3Measurement precision
If mixer cores are arranged to compensate for LO leakage, then signal-to-noise and distortion ratio improves, but physical layout complexity increases
Solution Approach 1:
The patent employs asymmetric signal routing and phase relationships among the mixer cores to achieve LO leakage cancellation. The differential signaling and specific interconnection patterns create asymmetric current paths that enable destructive interference of LO leakage while maintaining balanced signal processing, improving SNDR without requiring perfectly symmetric layouts that would be overly complex.
Data Source
Figure 1A~1B
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AI summary
Systems and methods are disclosed for compensating local oscillator leakage in a mixer. An example mixer includes a first double-balanced mixer core and a second double-balanced mixer. The first double-balanced mixer may comprise differential output nodes and may be configured to mix a first input signal with a first local oscillator signal. The second double-balanced mixer core may comprise second differential output nodes and may be configured to mix a second input signal with a second local oscillator signal. The second input signal may be approximately 180° out of phase with the first input signal. The second local oscillator signal may be approximately 180° out of phase with the first local oscillator signal. The differential output nodes may be electrically connected to the second differential output nodes, and the first double-balanced mixer core and the second double-balanced mixer core may be arranged to compensate for local oscillator leakage.