Low Voltage Mixer Using Single Transistor Layer
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Solution Overview
Problem
Gilbert cell mixers face non-linearity issues with baseband-input devices when creating high amplitude radiofrequency signals and require high operating voltages due to double layers of transistors, making them unsuitable for low voltage integrated circuits.
Innovation Solution
A low voltage headroom mixer design with a single layer of transistors, utilizing high pass and low pass filters and feedback loops to regulate current, allowing operation at lower supply voltages and higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a traditional Gilbert cell mixer design with double layer of transistors is used, then the mixer can operate with standard transistor configurations, but the operating voltage becomes unacceptably high for low voltage integrated circuits
Solution Approach 1:
The patent extracts and removes one layer of transistors from the traditional Gilbert cell mixer structure. Specifically, the patent eliminates the need for baseband input transistors by directly coupling the baseband signal to the local oscillator transistors, thereby reducing the voltage headroom requirement while maintaining mixer functionality
Solution Approach 2:
The patent merges the functions of baseband signal coupling and local oscillator switching into a single transistor layer. The local oscillator transistors simultaneously perform both the switching function and the baseband signal modulation, eliminating the need for separate baseband input transistors and reducing the overall voltage requirement
2Power
If baseband-input devices are used to create high amplitude radiofrequency signals, then signal amplitude is sufficient, but non-linearity issues arise in the mixer operation
Solution Approach 1:
The patent introduces feedback mechanisms through the differential pair configuration where the tail current source provides automatic current regulation. The differential structure inherently provides linear operation by distributing the input signal across two transistors, reducing non-linearity effects while maintaining sufficient output amplitude
Solution Approach 2:
The patent changes the operating parameters of the mixer by using a current-mode differential architecture instead of voltage-mode operation. This allows the mixer to achieve high amplitude output signals while maintaining linearity through proper current biasing and differential signal processing
3Reliability
If double layer of transistors with forward voltage of 100s of milli-volts is used, then transistor saturation mode is maintained, but the minimum required output voltage becomes unacceptably high
Solution Approach 1:
The patent removes the baseband input transistor layer that requires significant forward voltage drop. By directly coupling the baseband signal to the local oscillator transistors, the patent eliminates the cumulative voltage requirement of two transistor layers, reducing the minimum output voltage to acceptable levels for low voltage integrated circuits
Solution Approach 2:
The patent transitions from a two-layer vertical transistor structure to a single-layer structure with differential signaling. This dimensional change in the circuit architecture allows maintaining transistor saturation operation with reduced voltage headroom by utilizing the differential voltage swing instead of single-ended voltage drops
Data Source
AI summary
A mixer comprising a pair of low frequency mixer inputs, a pair of high frequency mixer inputs, a pair of mixer outputs, four switching units, each switching unit comprising a low frequency switching unit input, a high frequency switching unit input, a switching unit output, a node connected via a high pass filter to the respective high frequency switching unit input and via a low pass filter to the respective low frequency switching unit input and a switching device arranged to provide an output at the respective switching unit output in dependence on the voltage at the respective node, and comprising a first feedback loop responsive to the voltage at the first low frequency mixer input and arranged to regulate the current through the outputs of the first and second ones of the switching units so that the total current through the outputs of the first and second ones of the switching units is substantially proportional to the voltage at the first low frequency mixer input and a second feedback loop responsive to the voltage at the second low frequency mixer input and arranged to regulate the current through the outputs of the third and fourth ones of the switching units so that the total current through the outputs of the third and fourth ones of the switching units is substantially proportional to the voltage at the second low frequency mixer input.