Dynamic Current Steering Mixer for Low-Voltage Flicker Noise Suppression
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Solution Overview
Problem
Mixer circuits for high-frequency applications using metal oxide semiconductor (MOS) transistors face limitations due to limited voltage supply and high flicker noise, requiring increased gain and output signal levels, which conventional designs struggle to meet effectively.
Innovation Solution
A dynamic current steering mixer is introduced, comprising a Gilbert cell mixer core, load devices, a dynamic current steering cell, and a transconductor cell, where the dynamic current steering cell alternately steers current to or away from the Gilbert cell mixer core, effectively suppressing flicker noise by controlling current flow based on a control signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional double balanced mixer circuits are used, then the circuit structure is simple, but the flicker noise is high and the gain is insufficient
Solution Approach 1:
The mixer circuit is divided into multiple functional blocks: a first mixer stage with differential pairs, a second mixer stage with additional differential pairs, and interconnected current paths. This segmentation allows each stage to contribute differently to signal mixing while isolating noise sources, thereby reducing overall flicker noise without significantly increasing complexity
Solution Approach 2:
An intermediate current path is introduced between the first and second mixer stages, where currents from both stages are combined through shared current sources and load impedances. This intermediary structure enables noise cancellation through differential signaling while maintaining signal integrity and gain
2Use of energy by moving object
If MOS transistors are used in mixer circuits, then the voltage supply is limited to less than 2V, but the flicker noise is high
Solution Approach 1:
The circuit employs dynamic biasing where current sources are modulated at twice the local oscillator frequency to dynamically adjust the operating points of the MOS transistors. This dynamic operation allows the circuit to maintain low-voltage operation while optimizing the transistor operating conditions to minimize flicker noise generation
Solution Approach 2:
The mixer uses periodic switching of current paths synchronized with the local oscillator signal and its harmonics. Current is periodically steered through different transistor paths during each RF cycle, allowing the circuit to achieve high gain at low supply voltages while the periodic operation averages out flicker noise components
3Power
If gain is increased to compensate for limited voltage supply, then the output signal level improves, but the flicker noise increases
Solution Approach 1:
The output signals from the first and second mixer stages are combined through a summing node where currents are algebraically added. This merging of multiple signal paths with different noise characteristics achieves constructive addition of signal components while destructive interference reduces the overall flicker noise floor, providing high gain with improved noise performance
Data Source
AI summary
A dynamic current steering mixer. The dynamic current steering mixer comprises a Gilbert cell mixer core, a pair of load devices, a dynamic current steering cell, and a transconductor cell. The Gilbert cell mixer core has first and second nodes, receives a first differential input signal, and provides a differential output signal at the first nodes thereof. The load devices are respectively coupled between the first nodes of the Gilbert cell mixer core and a first fixed voltage. The dynamic current steering cell has third nodes coupled to the second nodes and fourth nodes. The transconductor cell is coupled between the fourth nodes and a second fixed voltage and receives a second differential input signal. The dynamic current steering cell alternately steers current of the transconductor cell to or away from the Gilbert cell mixer core.