Single Mixer Current Control for Low-Noise LO Switching
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Solution Overview
Problem
Single mixers in transceiver designs face significant noise challenges due to DC current flowing through the switching stage during local oscillator polarity changes, limiting the dynamic range of the receiver.
Innovation Solution
The integration of a current control circuit that modulates the current in the switching stage, particularly during local oscillator polarity changes, to reduce noise without affecting the mixer's gain, using transistors and resistors to form a current control circuit and current sources that adjust the DC current path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If DC current flows through the switching stage during local oscillator polarity changes, then the mixer operates normally, but significant noise is generated
Solution Approach 1:
The patent applies dynamics by making the DC current through the switching stage variable rather than fixed. A control voltage signal at twice the local oscillator frequency modulates the tail current source, dynamically adjusting the current level to be high during signal transitions and low during polarity changes, thereby reducing noise while maintaining proper operation
Solution Approach 2:
The patent implements periodic action by applying a control voltage signal at twice the local oscillator frequency to the tail current source. This periodic modulation causes the DC current to vary in sync with the local oscillator polarity changes, reducing current during noisy transitions and maintaining it during useful signal periods
2Object-affected harmful factors
If current is reduced in the switching stage during polarity changes, then noise is reduced, but mixer gain may be affected
Solution Approach 1:
The dynamic current control is timed to reduce current only during local oscillator polarity changes when no useful signal is present, while maintaining higher current levels during periods when the mixer is processing signals. This temporal differentiation allows noise reduction without sacrificing mixer gain
Solution Approach 2:
The control mechanism anticipates the local oscillator polarity changes and preemptively reduces the tail current before the noisy transitions occur. By preparing the current reduction in advance of the harmful event, the system prevents noise generation while preserving gain during signal processing periods
Data Source
AI summary
The system and method of the present invention provide a single mixer (200-400) with significantly reduced noise performance at a low cost by adding a current control circuit (109) that reduces the current in at least the switching stage (103, 303, 403) during polarity changes of the local oscillator (LO) signal (104). Alternative embodiments (300-400) are provided for a single mixer having significantly reduced noise wherein the low-noise characteristic is enhanced by a further modification to the switching stage (303-403).