Collector Current Driver for Bipolar Transistor Temperature Sensor
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Solution Overview
Problem
Integrated PNP bipolar transistor temperature transducers face significant errors in temperature measurement due to variations in the current gain factor β, which are exacerbated in integrated circuits where β values are typically low, leading to inaccuracies in collector current monitoring.
Innovation Solution
A collector current driver is implemented, utilizing current mirrors and differential amplifiers to maintain a target collector current despite temperature and β variations, by replicating and controlling the emitter current to ensure accurate collector current regulation, thereby compensating for β variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If emitter current is used to determine collector current in integrated PNP bipolar transistors, then the temperature transducer can be implemented inexpensively, but measurement precision deteriorates due to low β values causing significant errors in collector current ratio
Solution Approach 1:
The patent introduces an intermediary PNP bipolar transistor (the second transistor) that replicates the collector current of the temperature sensing transistor. This intermediary transistor serves as a mediator to indirectly measure the collector current without requiring direct access to the collector terminal, thereby maintaining measurement precision while keeping the implementation inexpensive and integrated.
Solution Approach 2:
The patent creates a copy of the collector current using a second PNP bipolar transistor that is configured to replicate the collector current of the first transistor. By copying the current through a matched transistor pair and using current mirrors, the system accurately determines the collector current ratio without being affected by β variations, thus improving temperature measurement precision.
2Measurement precision
If direct monitoring of collector current is implemented for integrated PNP devices, then measurement precision improves, but device complexity increases due to additional package pins and PCB traces
Solution Approach 1:
The patent uses a second PNP bipolar transistor as an intermediary device that provides indirect access to the collector current information. This mediator allows precise monitoring of collector current through the emitter terminal, eliminating the need for additional package pins and external circuit board traces, thus maintaining measurement precision while reducing device complexity.
Solution Approach 2:
The patent creates a current copy through a second transistor and current mirror circuits that replicate the collector current of the temperature sensing transistor. This copied current can be measured through the emitter terminal, providing accurate collector current monitoring without requiring direct collector access, thereby avoiding additional package and PCB complexity.
3Measurement precision
If collector current ratio accuracy is improved to enhance temperature measurement precision, then measurement precision improves, but device complexity increases due to additional monitoring circuits
Solution Approach 1:
The patent makes the second PNP bipolar transistor and associated circuits serve multiple functions: they replicate the collector current for measurement purposes, provide β compensation, and enable temperature sensing. This multi-functionality improves temperature measurement precision through accurate collector current ratio determination while minimizing additional circuit complexity by consolidating functions into existing transistor structures.
Solution Approach 2:
The second transistor acts as an intermediary that simultaneously achieves collector current replication and β compensation. Through this mediator, the system obtains accurate collector current ratio information for temperature measurement without requiring separate complex monitoring circuits, thus improving precision while keeping the circuit relatively simple.
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 effectively stabilizes the collector current, reducing measurement errors and maintaining accuracy across varying β values, even in integrated circuits with low β values, by using current mirrors and differential amplifiers to control emitter and collector currents.
Implementation Method 1
A current mirror is configured to receive the emitter current and provide a duplicate current equaling the emitter current
Implementation Method 2
A differential amplifier is configured to amplify a difference between the first voltage and a second voltage to provide an output voltage
Implementation Method 3
bipolar transistors have an emitter-to-base voltage (Veb) that varies predictably with regard to temperature
Data Source
AI summary
In one embodiment, a collector current driver is provided that controls the collector current for a bipolar transistor temperature transducer. The collector current driver is configured to use negative feedback to generate an emitter current for the bipolar transistor responsive to target current.