Self-Cascode MOSFET Voltage Reference for Low Power CMOS
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Solution Overview
Problem
Existing voltage references, particularly in battery-powered systems, face challenges in minimizing power consumption both during normal operation and low-power modes, and are often costly due to the use of BiCMOS processes and large area resistors, which increase the area and cost of integrated circuits.
Innovation Solution
A programmable CMOS-compatible low-power voltage reference is developed using a self-cascode metal-oxide semiconductor field-effect transistor (MOSFET) structure with a temperature compensated current source, allowing for digital trimming to generate reference voltages that are PTAT, ZTAT, or CTAT, and are suitable for various analog circuits, reducing power consumption and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bandgap voltage references employ bipolar junction transistors (BJTs) to generate reference voltage, then temperature independence and power supply rejection ratio are improved, but power consumption and manufacturing cost increase
Solution Approach 1:
The patent extracts the essential function of generating a temperature-independent reference voltage from bipolar transistors and implements it using only CMOS components. The self-cascode MOSFET structure replaces the BJT-based bandgap reference, eliminating the need for expensive BiCMOS processes while maintaining temperature stability through the specific MOSFET configuration and compensation circuitry.
Solution Approach 2:
The patent replaces expensive bipolar transistors and BiCMOS processes with cheaper CMOS transistors. Although CMOS processes are generally less precise for analog references, the self-cascode structure compensates for this by providing excellent temperature stability and power supply rejection, achieving comparable performance at lower cost and power consumption.
2Use of energy by moving object
If large area resistors are used in bandgap voltage references to provide low current, then power consumption is reduced, but IC area and manufacturing cost increase
Solution Approach 1:
The patent changes the operating parameters of the MOSFETs in the self-cascode structure to achieve low power consumption without requiring large resistors. By optimizing the transistor dimensions, bias currents, and threshold voltages, the circuit achieves stable reference voltage with minimal current draw, eliminating the need for area-consuming large-value resistors while maintaining low power operation.
3Ease of manufacture
If CMOS processes are used instead of BiCMOS processes, then manufacturing cost is reduced, but achieving low power consumption with stable reference voltage becomes more difficult
Solution Approach 1:
The self-cascode MOSFET structure is inherently self-compensating for temperature variations and power supply changes. The circuit automatically adjusts its operating point to maintain a stable reference voltage without requiring external compensation components or complex biasing circuits. This self-regulating behavior enables CMOS implementation to achieve bipolar-like stability at lower cost and power consumption.
Data Source
AI summary
A programmable voltage reference includes a temperature compensated current source and a voltage reference circuit. The temperature compensated current source includes an output configured to provide a reference current. The voltage reference circuit includes an input coupled to the output of the temperature compensated current source and a reference output. The voltage reference circuit includes a self-cascode metal-oxide semiconductor field-effect transistor structure that includes a first device that is diode-connected and operates in a weak inversion saturation region and a second device that operates in a weak inversion triode region. A length of the second device is selectable. The voltage reference circuit is configured to provide a reference voltage on the reference output based on the reference current.