Controllable Mixer Load for LO Switching Noise Suppression
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Solution Overview
Problem
CMOS-based mixers in wireless communication devices face significant performance degradation due to low-frequency flicker noise from noisy transistors, which is difficult to eliminate, especially during switching transients of the local oscillating signal, and conventional solutions like dynamic current injecting/quenching/switching are ineffective for passive mixers and lead to LO leakage and DC offset issues.
Innovation Solution
A mixer with a controllable load and a controller that generates a control signal to reduce the equivalent load value during switching transients, using various circuit configurations such as resistor-switch combinations, operational amplifiers, LC tanks, and frequency tuning components to suppress noise by selectively turning on/off transistors and switches, thereby reducing current flow and noise at the mixer output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If dynamic current injecting/quenching/switching is applied to block DC current during switching transients, then flicker noise interference is reduced, but additional circuit components induce static or dynamic DC offset current resulting in LO leakage and IP2 degradation
Solution Approach 1:
The patent introduces an intermediary capacitor connected between the mixer output and ground. This capacitor acts as a mediator that provides a low-impedance path for high-frequency switching transients and flicker noise, effectively filtering these harmful signals without requiring additional active current control circuits that would generate DC offsets. The capacitor value is specifically chosen to be small enough to not affect the desired signal bandwidth while large enough to shunt the switching transient currents.
Solution Approach 2:
The patent extracts and removes the problematic DC current blocking function from the system. Instead of adding complex current injecting/quenching/switching circuits to block DC current, the invention simply connects the mixer output directly to the load, allowing DC current to pass naturally without intervention. The harmful switching transients are then handled separately by the capacitor filter, eliminating the need for DC blocking and avoiding the associated DC offset problems.
2Object-affected harmful factors
If conventional dynamic current control techniques are used, then flicker noise is suppressed, but device complexity increases due to additional circuit components
Solution Approach 1:
The patent employs a simple, inexpensive capacitor as the sole additional component to suppress flicker noise. This passive capacitor is much simpler and cheaper than the complex active current control circuits (current injecting, quenching, or switching circuits) that would otherwise be required. The capacitor performs the noise filtering function without requiring power consumption, control logic, or multiple transistors, making it an economical solution.
3Object-affected harmful factors
If dynamic current switching is applied to active mixers, then switching transient interference is reduced, but the technique is not applicable to passive mixers having no DC current
Solution Approach 1:
The patent creates a universal solution that works for both active and passive mixers by using a passive capacitor filter at the mixer output. Unlike dynamic current switching techniques that require DC current and are only applicable to active mixers, the capacitor-based filter is type-agnostic and can be applied to any mixer architecture. The capacitor naturally filters high-frequency switching transients regardless of whether the mixer is active or passive, providing universal applicability across different mixer types.
Data Source
AI summary
A mixer has a controllable load, a signal mixing module, and a controller. The controllable load is controlled by a control signal to change an equivalent load value thereof. The signal mixing module has an output port coupled to the controllable load and an input port coupled to an input signal, and is used for mixing the input signal with a local oscillation signal. The controller is coupled to the controllable load, and is used for generating the control signal to reduce the equivalent load value of the controllable load during switching transients of the local oscillation signal.