Programmable Resistor Array for Continuous Time PGA Filter
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Solution Overview
Problem
CMOS transmission gate switches are unsuitable for continuous time operation due to nonlinear region issues near the center of the power supply voltage range, limiting their use in rail-to-rail circuit operations and requiring innovative solutions to maintain gate dielectric integrity and ensure linear operation.
Innovation Solution
A programmable resistor array circuit with a programmable gain amplifier filter, incorporating a voltage doubler circuit and gate boosted switches that use a threshold voltage sense transistor to maintain linear operation and prevent excessive gate dielectric voltage, allowing for user-selectable bandwidth and reliable continuous time operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMOS transmission gate switches are used for rail-to-rail operation, then voltage range is extended, but nonlinear region issues occur near the center of the power supply voltage range
Solution Approach 1:
The patent introduces an intermediary circuit that includes a sense transistor and control logic that mediates between the power supply voltage range extension and the linearity requirement. The sense transistor detects the voltage range and controls the switching elements to remain in the linear region, preventing nonlinear operation near the center of the power supply voltage range while still enabling rail-to-rail operation.
Solution Approach 2:
The patent changes the operating parameters of the MOS switches by dynamically adjusting their gate voltages based on the detected voltage range. The control circuit modifies the gate voltage parameters to ensure that the switches operate in the linear region across the entire rail-to-rail voltage range, avoiding the nonlinear region that would otherwise occur near the center of the power supply voltage range.
2Adaptability or versatility
If gate voltage is increased to extend voltage range, then power supply flexibility is improved, but gate oxide integrity reliability is compromised
Solution Approach 1:
The patent implements a feedback mechanism using a sense transistor that continuously monitors the voltage range and provides feedback to the control circuit. This feedback enables the system to adjust the gate voltages of the switching elements in real-time, ensuring that the gate oxide integrity is maintained by preventing excessive voltage stress while still allowing flexible rail-to-rail operation.
Solution Approach 2:
The patent applies beforehand cushioning by designing the control circuit to preemptively adjust gate voltages before excessive voltage stress can damage the gate oxide. The sense transistor and control logic prepare the switching elements by maintaining them in the linear region with appropriate gate voltages, cushioning against potential gate oxide damage before it can occur during rail-to-rail operation.
Data Source
AI summary
A compensation circuit includes an amplifier coupled between a first voltage terminal and a common terminal. The amplifier has a first output terminal. A current source transistor has a current path coupled between a second voltage terminal and a second output terminal. A threshold voltage sense transistor has a current path coupled between the first and second output terminals. A gate and drain of the threshold voltage sense transistor are connected. An output transistor having a current path coupled between the first output terminal and a third output terminal has a gate coupled to the second output terminal.