Single-Sideband Mixer With Midpoint Common-Mode Output
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Solution Overview
Problem
Conventional single sideband mixers require AC coupling and protection circuits due to high common-mode voltage and potential transistor damage, making DC coupling and protection circuit-free operation desirable.
Innovation Solution
Incorporating complementary Gilbert cell mixers and a cross-coupling inverter pair to manage signal phases and voltages, allowing DC coupling with the subsequent circuit without the need for protection circuits, and configuring the load to resonate at the sum or difference frequency of the input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC coupling is used to interface with the subsequent circuit, then the high common-mode voltage is isolated, but the system complexity increases and DC coupling capability is lost
Solution Approach 1:
The patent changes the common-mode voltage parameter from high (VDD) to low (midpoint between VDD and VSS) by using complementary Gilbert cell mixers with cross-coupling inverters. This parameter transformation eliminates the need for AC coupling while maintaining protection benefits, allowing direct DC coupling to subsequent circuits.
2Reliability
If protection circuits are added to prevent transistor damage, then transistor reliability improves, but device complexity increases
Solution Approach 1:
The patent converts the potentially harmful high common-mode voltage swing into a beneficial feature by using cross-coupling inverter pairs that actively maintain the output common-mode voltage at a safe midpoint level. The harmful voltage excursions are transformed into a stable operating condition that inherently protects transistors without requiring separate protection circuits.
3Ease of operation
If the common-mode voltage is maintained at VDD level, then the mixer operates with standard voltage levels, but the subsequent circuit cannot tolerate the high voltage and AC coupling is required
Solution Approach 1:
The patent segments the voltage domain management by using separate complementary Gilbert cell mixers for different signal paths, with cross-coupling inverter pairs that specifically manage the common-mode voltage level. This segmentation allows the mixer core to operate at standard voltage levels while the output interface actively transforms the voltage to a safe level for subsequent circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution stabilizes the common-mode voltage at a midpoint, preventing transistor damage and enabling reliable DC coupling, thus simplifying the system and reducing complexity.
Implementation Method 1
a load placed across the first node and the second node and configured to resonate at a frequency approximately equal to either a sum of a frequency of the first signal and a frequency of the second signal or a difference of the frequency of the first signal and the frequency of the second signal
Data Source
AI summary
A circuit having a first Gilbert cell mixer of a first type configured to receive phases of first and second signals and output a first current pair to a first node and a second node; a first Gilbert cell mixer of a second type configured to receive output a second current pair to the first node and the second node; a second Gilbert cell mixer of the first type configured to receive phases of the first and second signals and output a third current pair to the first node and the second node; a second Gilbert cell mixer of the second type configured to output a fourth current pair to the first node and the second node; a cross-coupling inverter pair configured to cross couple the first node and the second node; and a load placed across the first node and the second node and configured to resonate at a frequency approximately equal to either a sum of a frequency of the first signal and a frequency of the second signal or a difference of the frequency of the first signal and the frequency of the second signal.