CMOS Replica Transistor Feedback for ON Current Stability
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Solution Overview
Problem
As semiconductor devices miniaturize and voltage levels decrease, variations in threshold voltages of transistors increase, leading to larger fluctuations in ON current, which affect standby current and are difficult to manage, especially due to temperature changes.
Innovation Solution
A method and semiconductor device that utilize replica transistors and control circuits to maintain ON and OFF current values at target levels by adjusting power-supply and substrate voltages, using diode-connected replica transistors and feedback mechanisms to stabilize current flows in CMOS circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If miniaturization and voltage lowering are implemented, then device integration and power efficiency are improved, but transistor threshold voltage variations increase causing ON current fluctuations
Solution Approach 1:
The patent implements a feedback mechanism where a replica transistor mirrors the characteristics of the actual transistor, and the measured current from the replica is fed back through an amplifier to adjust the gate voltage of the actual transistor, compensating for threshold voltage variations and stabilizing ON current
Solution Approach 2:
The patent uses a replica transistor that copies the electrical characteristics of the actual transistor to sense and measure current variations. This replica serves as a model to predict and compensate for threshold voltage fluctuations in the main transistor without directly affecting its operation
2Productivity
If miniaturization is implemented, then device density is improved, but threshold voltage variations among transistors increase
Solution Approach 1:
The patent applies local compensation by providing individual feedback control to each transistor or transistor group through dedicated replica transistors and amplifiers, allowing threshold voltage variations to be corrected locally rather than requiring global uniformity across the entire chip
Solution Approach 2:
The patent dynamically adjusts the gate voltage parameter of the actual transistor based on measured current variations from the replica transistor, compensating for manufacturing variations by changing the operating parameters rather than relying on precise manufacturing control
3Speed
If threshold voltage is lowered to improve speed, then switching speed is improved, but OFF current increases affecting standby current
Solution Approach 1:
The patent dynamically adjusts transistor operating conditions using feedback control, allowing the system to optimize between speed and power consumption based on actual operating conditions rather than using fixed threshold voltages, enabling low threshold voltage for speed when needed while maintaining acceptable standby current
Data Source
AI summary
A method for controlling power supply current in a CMOS circuit, the method including applying a first predetermined voltage to a diode connected n-channel replica transistor, the n-channel replica transistor operating in weak inversion, applying a first substrate voltage to the substrate of the n-channel replica transistor so that the current flowing in the n-channel replica transistor equals a first predetermined target current, and applying the first substrate voltage to substrates of n-channel transistors in the CMOS circuit.