Short-Duty-Clock Switched Resistor for PVT-Stable CMOS Resistance
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Solution Overview
Problem
Sensor interface circuits face challenges in maintaining accuracy and linearity due to process, voltage, and temperature variations, particularly in implementing large resistance values without incurring significant silicon area costs or introducing noise penalties.
Innovation Solution
A short-duty-cycle clock is used in conjunction with a switched-resistor circuit to boost resistance levels and mitigate variations, employing a programmable resistor-capacitor delay unit and inverters to generate a clock that tracks resistance changes over temperature, thereby maintaining a constant frequency and reducing silicon area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If large resistance values are implemented using traditional poly resistors, then the resistance level is achieved, but the silicon area becomes excessively large
Solution Approach 1:
The patent employs periodic switching action where a switch toggles between closed and open states at specific clock cycles. By keeping the switch closed only during specific periods (when the clock signal is active), the circuit achieves an equivalent resistance much larger than the physical resistor value, while the switch remains compact in silicon area. This periodic action transforms a spatial problem (large area) into a temporal problem (time-based switching).
Solution Approach 2:
The patent introduces a clock signal as an intermediary that controls the switching element. This clock signal mediates between the physical resistor and the rest of the circuit, enabling the resistor to be effectively 'removed' from the continuous path during most time periods. The clock-driven switch acts as a mediator that creates the illusion of a much larger resistance without requiring the physical space for a large resistor.
2Area of stationary object
If switched-capacitor circuits are used to implement large resistance, then silicon area is reduced, but noise penalties are introduced
Solution Approach 1:
The patent uses a simple switch element that can be implemented with standard CMOS transistors, which are inexpensive and compact compared to switched-capacitor circuits. The switch is 'disposable' in the sense that it only needs to be conductive during specific short time periods, allowing for simpler, lower-noise implementation. This approach trades the continuous operation of switched-capacitor circuits for intermittent switching, reducing noise while maintaining area efficiency.
3Device complexity
If standard clock cycles are used, then the circuit operation is simple, but temperature variations cause resistance drift
Solution Approach 1:
The patent implements a feedback mechanism where the clock signal's duty cycle is dynamically adjusted based on temperature sensing. The system monitors temperature variations and automatically modifies the proportion of time the switch remains closed, compensating for temperature-induced resistance changes. This feedback loop maintains stable equivalent resistance across temperature variations while keeping the overall circuit structure relatively simple.
Solution Approach 2:
The patent changes the temporal parameter (duty cycle) of the clock signal in response to temperature variations. By adjusting what percentage of each clock period the switch remains closed, the system compensates for temperature effects on resistance. This parameter modulation allows the circuit to adapt to environmental changes without requiring complex hardware modifications, maintaining both simplicity and stability.
Data Source
AI summary
Implementation of large temperature-insensitive resistance in CMOS using short-duty-clock cycle is provided herein. Operations of a method can comprise boosting a resistance level of a switched-resistor circuit to a defined resistance level. The boosting can comprise using a short-duty-cycle clock to facilitate the boosting. Also provided is a sensor system that can comprise a short-duty-cycle clock and a switched-resistor circuit. The short-duty cycle clock boosts a resistance level of the switched-resistor circuit to a defined resistance level.