CMOS Threshold Voltage Extraction Circuit for Low Power
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Solution Overview
Problem
Existing CMOS threshold voltage measurement techniques face challenges in low power supply voltage applications and are not suitable for radiation-hardened environments, as they often require diodes or complex components that are difficult to design and prone to degradation.
Innovation Solution
A circuit using current mirrors and well-matched transistors and resistors to extract CMOS threshold voltage, which operates with a low voltage supply and is resistant to radiation, employing a simple configuration with few components that takes advantage of the square law equation for temperature sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a diode is used for temperature compensation, then temperature sensing capability is achieved, but the voltage range requirement increases to 600-800mV making buffer/opamp design more difficult in low power supply voltage applications
Solution Approach 1:
The patent changes the sensing parameter from diode voltage (requiring 600-800mV) to transistor threshold voltage (Vt), which can be sensed at lower voltages. By using the relationship Vt = Vgs - Id*Rd and measuring Vgs across a transistor, the circuit achieves temperature sensing capability with lower voltage requirements suitable for low power supply voltage applications.
2Measurement precision
If complex components are used for threshold voltage measurement, then measurement accuracy is improved, but device complexity and radiation hardness decrease
Solution Approach 1:
The patent segments the measurement function into simple, modular components: current mirrors for current replication, matched transistors for voltage comparison, and resistors for current-to-voltage conversion. This segmentation achieves accurate threshold voltage measurement while keeping each component simple and radiation-hardened, avoiding the need for complex integrated measurement circuits.
3Measurement precision
If matched transistors and resistors are used in current mirror configuration, then threshold voltage extraction accuracy is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent merges the threshold voltage extraction function with the existing current mirror structure. By combining the current mirror's inherent current replication capability with matched transistors operating in saturation, the circuit extracts Vt through the relationship Vgs = Vt + Id*Rd. This merging achieves accurate extraction while utilizing standard matched transistor pairs already present in CMOS processes, reducing additional manufacturing precision requirements.
Data Source
AI summary
The disclosure is directed to a simple, inexpensive circuit to extract the complementary metal-oxide-semiconductor (CMOS) threshold voltage (Vt) from an integrated circuit. The threshold voltage may be used elsewhere in the circuit for a variety of purposes. One example use of threshold voltage is to sense the temperature of the circuit. The CMOS Vt extraction circuit of this disclosure includes a current mirror and an arrangement of well-matched transistors and resistors that takes advantage of the square law equation. The structure of the circuit may make it well suited to applications that benefit from low-power radiation hardened circuits.