Resistorless PTAT Cell for Low Power Voltage Reference
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Solution Overview
Problem
Conventional bandgap voltage reference circuits are sensitive to process variations and noise, and they require large resistors that occupy significant silicon area, making them costly and inefficient for low-power applications.
Innovation Solution
A resistorless PTAT cell is developed using a configuration of transistors with different current densities, which minimizes sensitivity to process variations and noise, and allows for fine-tuning and scaling of the reference voltage, reducing silicon area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap voltage reference circuits use large resistors to generate PTAT voltage, then the voltage reference stability is improved, but the silicon area occupied increases and power consumption increases
Solution Approach 1:
The patent extracts and eliminates the large resistor component from the conventional bandgap circuit by implementing a resistorless PTAT voltage generation method using only active devices (transistors), thereby removing the source of large silicon area occupation while maintaining PTAT voltage generation capability
Solution Approach 2:
The patent substitutes the passive resistor-based PTAT voltage generation mechanism with an active device-based mechanism using transistors operating in specific regions, replacing the mechanical/resistive system with a semiconductor active system that achieves the same functional outcome without the area penalty
2Power
If conventional bandgap voltage reference circuits use large resistors, then PTAT voltage is generated, but power consumption increases making it unsuitable for low-power applications
Solution Approach 1:
The patent removes the energy-inefficient resistor component from the circuit, extracting the problematic element that causes excessive power consumption while preserving the essential PTAT voltage generation function through active device manipulation
Solution Approach 2:
The patent changes the operating parameters and mechanisms of the transistors (biasing conditions, operating regions, current densities) to enable PTAT voltage generation without relying on resistive heating, thereby fundamentally altering how power is utilized in the circuit
3Reliability
If conventional bandgap voltage reference circuits are implemented, then voltage reference is provided, but sensitivity to process variations and noise increases
Solution Approach 1:
The patent replaces the resistor-based mechanism with an active device-based mechanism that is inherently less sensitive to process variations and noise, substituting a noisy passive component system with a controlled active system that can better reject disturbances
Solution Approach 2:
The circuit uses the inherent properties of the transistors and their interconnections to automatically compensate for and reject noise and process variations, allowing the system to self-correct without external intervention or additional noisy components
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a stable voltage reference with reduced noise and process sensitivity, occupying less silicon area and being compatible with low-power applications, while maintaining consistency across a wide temperature range.
Implementation Method 1
The voltage drop across the diode has a negative temperature coefficient, TC, of about −2.2 mV/° C. and is usually denoted as a Complementary to Absolute Temperature (CTAT) voltage, since its output value decreases with increasing temperature.
Implementation Method 2
The PTAT current is generated by reflecting across a resistor a voltage difference (ΔVbe) of two forward-biased base-emitter junctions of bipolar transistors operating at different current densities.
Data Source
AI summary
Circuits for generating a PTAT voltage as a base-emitter voltage difference between a pair of bipolar transistors. The circuits may form unit cells in a cascading voltage reference circuit that increases the PTAT voltage with each subsequent stage. The bipolar transistors are controlled using a biasing arrangement that includes an MOS transistor connected to a current mirror that provides the base current for the bipolar transistors. A voltage reference is formed by combining a PTAT voltage and a CTAT voltage at the last stage. The voltage reference may be obtained from the voltage at an emitter of one of the bipolar transistors in the last stage.