Substrate BJT Collector Current Control Circuit
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Solution Overview
Problem
The integration of bipolar junction transistors (BJTs) and CMOS elements using BiCMOS process technology is costly and time-consuming, and controlling collector currents of substrate BJTs is challenging, especially when they are realized using CMOS process technology, as it degrades BJT characteristics and makes direct control of collector currents difficult.
Innovation Solution
A circuit comprising current mirrors and current sources is designed to control collector currents of substrate BJTs, including a first current mirror to generate a mirroring base current, a current transmitter to replicate this current, and a second current mirror to supply the replicated current to the emitter, allowing for precise control of collector currents, and another circuit to compensate base currents for generating proportional to absolute temperature (PTAT) voltage by using multiple current mirrors and transmitters to replicate and adjust base and collector currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If BiCMOS process technology is used to integrate CMOS elements and BJTs, then device functionality is improved, but fabrication cost and development time increase
Solution Approach 1:
The patent merges CMOS and BJT technologies by integrating substrate BJTs into a CMOS process flow, allowing both device types to coexist on the same chip without requiring separate BiCMOS fabrication lines, thereby reducing manufacturing complexity and cost while maintaining functional versatility
Solution Approach 2:
The invention creates a universal CMOS process that can produce both standard CMOS devices and substrate BJTs using the same fabrication infrastructure, enabling a single manufacturing line to serve multiple device types and applications, thus reducing development time and fabrication costs
2Ease of manufacture
If substrate BJTs are realized using CMOS process technology, then manufacturing complexity is reduced, but collector current control becomes difficult
Solution Approach 1:
The patent introduces an intermediary control mechanism where base current is used to control collector current in substrate BJTs. By manipulating the base terminal (which is accessible unlike the collector in substrate configurations), the invention enables indirect but effective control of collector current, resolving the difficulty of direct control in substrate BJTs
Solution Approach 2:
The invention implements feedback control circuits that monitor and adjust base current to maintain precise collector current levels in substrate BJTs. This feedback mechanism compensates for process variations and ensures accurate current control, making substrate BJTs as controllable as surface BJTs while maintaining CMOS manufacturing simplicity
3Area of stationary object
If substrate BJTs are used in circuits, then integration density is improved, but base current compensation becomes necessary
Solution Approach 1:
The patent uses current mirror circuits to create copies of reference currents and replicate them for base current compensation. By copying a stable reference current through matched transistor pairs, the invention generates compensated base currents that maintain accuracy while occupying minimal space, thus achieving high integration density without sacrificing compensation precision
Data Source
AI summary
A circuit for controlling a collector current of a substrate bipolar junction transistor (BJT) is provided. The circuit includes a first current mirror configured to generate a first mirroring base current corresponding to a replicate current of a base current of the substrate BJT, a current transmitter configured to transmit the first mirroring base current, a second current mirror configured to generate a second mirroring base current corresponding to a replicate current of the first mirroring base current received from the current transmitter and configured to supply the second mirroring base current to an emitter of the substrate BJT, and a current source configured to supply a drive current corresponding to a collector current of the substrate BJT to the emitter of the substrate BJT.