MOS Switch Circuit With Adjustable Common-Mode Linearity
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Solution Overview
Problem
Conventional switch circuits for relaying differential voltages restrict the linearity of linear circuits due to varying differential mode resistances with changes in differential input voltages, affecting their performance in applications like filters and amplifiers.
Innovation Solution
A linearity-adjustable switch circuit comprising a pair of metal oxide semiconductor (MOS) switches and an adjusting unit that alters the difference between common mode levels of the input and output terminals to adjust differential mode resistances, using current sources or resistors/capacitors/inductors to set common mode voltages and minimize variations in differential mode resistances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MOS switches are used to relay differential voltages, then the switch circuit can perform basic signal transmission, but the differential mode resistances vary with differential input voltages, restricting linearity of linear circuits
Solution Approach 1:
The patent introduces common mode voltage adjusting units as intermediary components between the differential input terminals and the MOS switches. These adjusting units (comprising voltage sources and resistors) mediate the voltage relationship by establishing controlled common mode voltage differences, which in turn control the gate-source voltages of the MOS switches to maintain constant differential mode resistances, thereby resolving the linearity issue without modifying the core switch structure
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the common mode voltage levels at the input and output terminals through the adjusting units. By changing the common mode voltage difference (Vdcm), the gate-source voltages of the MOS switches are controlled to maintain optimal operating points, ensuring that differential mode resistances remain constant despite variations in differential input voltages, thus improving linearity
2Reliability
If the differential mode resistances are kept constant to improve linearity, then linearity of linear circuits is enhanced, but the device complexity increases due to additional adjusting units
Solution Approach 1:
The patent segments the voltage control function into two independent parts: differential voltage signaling and common mode voltage adjustment. The adjusting units are separately connected to the input and output terminals, each independently controlling the common mode voltage level. This segmentation allows the constant resistance function to be achieved through distributed, modular components rather than a complex centralized control mechanism, thereby improving linearity with manageable complexity
Solution Approach 2:
The common mode voltage adjusting units serve multiple functions simultaneously: they establish the common mode voltage difference, control the gate-source voltages of the MOS switches, and maintain constant differential mode resistances. This multi-functionality reduces the need for additional dedicated components, achieving improved linearity without proportionally increasing circuit complexity
Data Source
AI summary
A switch circuit includes a pair of metal oxide semiconductor (MOS) switches and an adjusting unit. Each of the MOS switches has an input terminal and an output terminal. The MOS switches receive a pair of differential input voltages at the input terminals thereof, and output a pair of differential output voltages at the output terminals thereof when the MOS switches conduct. The adjusting unit changes a difference between common mode levels of the input terminals and the output terminals of the MOS switches so as to adjust linearity of differential mode resistances of the MOS switches.