On-Die Temperature Sensor Using PTAT Generator and Comparator
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Solution Overview
Problem
Conventional on-die temperature sensors require multi-temperature trimming due to random transistor mismatches, increasing test time and cost, and rely on A/D converters that add to the overall expense.
Innovation Solution
A temperature sensor circuit that employs a PTAT generator with a base-current mirror stage using differently sized npn transistor devices, a switched-capacitor ramp generator, and a high-speed comparator to measure temperature with reduced linearity issues and without the need for an A/D converter, allowing for potential single-temperature trimming and cost savings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PTAT generator with current-mirrored legs is used, then temperature measurement function is achieved, but random transistor mismatches cause non-linearity requiring multi-temperature trimming
Solution Approach 1:
The patent extracts and eliminates the problematic current-mirrored leg structure that causes transistor mismatch. Instead of using three separate current-mirrored legs with multiple transistors, the invention uses a simplified differential amplifier structure with only two transistors, removing the source of random mismatches while retaining the temperature measurement function.
Solution Approach 2:
The patent changes the fundamental circuit topology from a multi-transistor current-mirrored structure to a differential amplifier structure. This parameter change in circuit architecture eliminates the need for multi-temperature trimming by inherently providing better linearity through the differential configuration that compensates for process variations.
2Measurement precision
If conventional PTAT generator with current-mirrored legs is used, then temperature measurement function is achieved, but random transistor mismatches cause non-linearity increasing manufacturing complexity
Solution Approach 1:
The patent removes the complex current-mirrored leg structure with multiple transistors and resistors, extracting only the essential differential amplification function. This reduction in circuit elements directly lowers manufacturing complexity while maintaining measurement precision through the differential configuration.
Solution Approach 2:
Instead of using current-mirrored legs that require precise matching of multiple components, the patent inverts the approach by using a differential amplifier where mismatch compensation is inherent in the differential configuration, turning the problem of component variation into a solution.
3Ease of operation
If A/D converter is used to convert analog PTAT voltage to digital value, then temperature can be read digitally, but overall expense increases
Solution Approach 1:
The patent introduces a voltage divider as an intermediary component that directly converts the analog PTAT voltage into a digital-ready voltage level without requiring a complex A/D converter. This intermediary approach achieves digital compatibility with much lower cost and simpler manufacturing.
Solution Approach 2:
The patent replaces the expensive A/D converter with a simple, inexpensive voltage divider network that achieves the same functional goal of providing digital-compatible temperature readings. This substitution uses cheap passive components instead of expensive active conversion circuitry.
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 improved linearity and reduced variation in temperature measurement, potentially requiring only room temperature trimming and eliminating the need for an A/D converter, thus reducing manufacturing costs and complexity.
Implementation Method 1
a PTAT (proportional to absolute temperature) generator that generates an analog PTAT voltage that ideally is linearly proportional to temperature
Implementation Method 2
the base-to-emitter voltage difference ΔVBE between Q1 and Q2 is given by Equation (1) as follows: ΔVBE=VT*ln(m) where VT is the voltage equivalent of temperature
Implementation Method 3
the PTAT generator 100 has an operational amplifier (opamp) A whose two (positive and negative) inputs are generated by two current-mirrored legs configured in a negative-feedback arrangement
Implementation Method 4
the first leg comprises a first PMOS (p-type metal oxide semiconductor) transistor MP1 in series with a first pnp-type bipolar transistor device Q1, and the second leg comprises a second PMOS transistor MP2 in series with a first resistor R1 and a second pnp-type bipolar transistor device Q2
Data Source
AI summary
An on-die temperature sensor measures temperature during a temperature-measurement session. A PTAT (proportional-to-absolute-temperature) generator generates an analog PTAT voltage that is dependent on temperature. A ramp generator generates a changing, analog ramp voltage whose rate of change is dependent on the PTAT voltage, such that the rate of change of the ramp voltage is dependent on the temperature. A comparator compares the ramp voltage to a reference voltage to detect termination of the temperature-measurement session. A counter generates a count value based on the duration of the temperature-measurement session, where the count value is mapped to the measured temperature using a lookup table. The PTAT generator has (i) two npn-type bipolar devices that generate a base-to-emitter voltage difference that is dependent on temperature and function as an amplifier input stage and (ii) circuitry to generate base currents for the bipolar devices to avoid current loading at the PTAT output.