Temperature Sensor Circuit With Calibrated PTAT Reference
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Solution Overview
Problem
Conventional temperature sensors face challenges in achieving high-frequency updates due to limitations in current biasing of bipolar junction transistors, leading to inefficiencies in power consumption and area usage, and inaccuracies in temperature readings caused by non-ideal transistor performance.
Innovation Solution
A temperature sensing circuit utilizing an adjustable current source to generate a scaled current proportional to absolute temperature, which is used to produce an internal reference voltage, allowing for calibration and accurate digital temperature readouts through an analog to digital converter and digital circuit adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If bipolar junction transistors are biased at higher currents to achieve high-frequency updates, then sampling speed is improved, but power consumption and area increase due to transistor capacitance dominance
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component to buffer the voltage proportional to absolute temperature (Vptat) signal. This amplifier enables high-frequency sampling by providing low output impedance and high current drive capability, allowing the bipolar junction transistors to operate at lower currents while still achieving high sampling speeds. The amplifier acts as a mediator between the sensitive Vptat source and the high-speed sampling requirements.
2Speed
If multiple bipolar junction transistors are connected in parallel to increase bias current, then sampling speed is improved, but area and power consumption increase
Solution Approach 1:
The operational amplifier serves as a current buffer that enables single-transistor or few-transistor designs to achieve high sampling speeds without requiring large parallel transistor arrays. The amplifier provides the necessary current multiplication, eliminating the need to scale up transistor area to increase bias current.
Solution Approach 2:
The patent replaces the mechanical approach of increasing transistor area and parallel connectivity to increase current with an electronic approach using an operational amplifier. Instead of physically adding more transistors in parallel, the system uses the amplifier's current gain to achieve the same effect with minimal area increase.
3Measurement precision
If bipolar junction transistors are used to generate Vptat, then temperature sensing is achieved, but measurement accuracy deteriorates due to non-ideal transistor performance
Solution Approach 1:
The patent implements calibration mechanisms that use feedback to compensate for transistor non-idealities. The system measures the actual Vptat output and compares it against expected values, then adjusts calibration parameters to correct for systematic errors. This feedback-based calibration approach maintains high measurement accuracy despite variations in transistor performance.
Solution Approach 2:
The patent employs calibration techniques that adjust electrical parameters (such as offset voltages and gain factors) to compensate for transistor non-idealities. By changing these parameters based on measured performance, the system maintains accurate temperature measurements even when transistor characteristics deviate from ideal behavior.
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
Enables faster and more accurate temperature sensing with reduced power and area consumption, overcoming limitations of previous designs by allowing higher sampling speeds and improved calibration techniques.
Implementation Method 1
A voltage proportional to absolute temperature Vptat can be produced as the difference between the base-emitter junction voltages of two bipolar junction transistors biased at different current densities. Mathematically, this can be represented as: Vptat = ΔVbe = Vbe1-Vbe2.
Implementation Method 2
An operational amplifier 11 has its non-inverting terminal connected to node N2, its inverting terminal connected to node N1, and its output connected to the gates of p-channel transistors MP1 and MP2.
Data Source
AI summary
A temperature sensing circuit includes a current generation circuit generating an initial current proportional to absolute temperature (Iptat), and a voltage generation circuit configured to mirror Iptat using an adjustable current source to produce a scaled current and to source the scaled current to a first terminal of a resistor to produce a reference voltage at the first terminal. A second terminal of the resistor has a voltage complementary to absolute temperature (Vctat) applied thereto. An analog-to-digital converter (ADC) has a reference input receiving the reference voltage, and a data input receiving Vctat or an externally sourced voltage. The ADC generates an output code indicative of a ratio between: a) either Vctat or the externally sourced voltage, and b) the reference voltage. A digital circuit determines a temperature readout from the output code and calibrates the reference voltage and the temperature readout determination based upon the output code.