Flipped Gate Current Reference Circuit Noise Immunity
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Solution Overview
Problem
Current current reference circuits using bipolar junction transistors (BJTs) are susceptible to substrate noise, and temperature-dependent resistor solutions have limitations in maintaining a constant reference current over a wide temperature range.
Innovation Solution
A current reference circuit incorporating a flipped gate transistor, a tracking voltage generator, and a control resistor with temperature-independent resistance, along with a current mirror and amplifier, to maintain a constant reference current by adjusting the conductivity of control transistors and mirroring the reference current to external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bipolar junction transistors (BJTs) are used to form bandgap references, then a reference voltage signal can be provided, but the circuit becomes susceptible to substrate noise (majority carrier noise for PNP BJTs and minority carrier noise for NPN BJTs)
Solution Approach 1:
The patent introduces an isolated well structure as an intermediary between the BJT and the substrate. This isolated well acts as a mediator that blocks the propagation of substrate noise to the transistor, thereby reducing susceptibility to harmful noise factors while maintaining the reference voltage generation function
Solution Approach 2:
The patent segments the substrate into isolated regions using separate wells for different transistor types (PNP and NPN). By dividing the substrate into electrically isolated segments, noise from one region does not affect transistors in other regions, thereby reducing overall substrate noise susceptibility
2Temperature
If temperature-dependent resistor solutions are used to compensate for temperature effects, then temperature dependency can be reduced, but the circuit complexity increases and manufacturing precision requirements increase
Solution Approach 1:
The patent changes the temperature dependence parameter of resistors by selecting specific resistor types (e.g., diffusion resistors with positive temperature coefficient) and configuring them in specific arrangements (series/parallel combinations) to compensate for temperature effects on transistor parameters, thereby maintaining reference current stability
Solution Approach 2:
The patent merges temperature compensation functionality directly into the reference current generation circuit by integrating temperature-dependent resistors with the transistor network. This combination eliminates the need for separate compensation circuits, reducing overall device complexity while maintaining temperature stability
Data Source
AI summary
A current reference which includes a tracking voltage generator including a flipped gate transistor, a first transistor connected with the flipped gate transistor in a Vgs subtractive arrangement, an output node providing a tracking voltage which has a positive or negative temperature dependency based on the flipped gate transistor and the first transistor, and a second transistor connected to the output node; an amplifier to receive the tracking voltage and output an amplified signal; a control transistor to receive the amplified signal; a control resistor connected in series with the control transistor; and a current mirror to receive and mirror a reference current to at least one external device, the current mirror including mirroring pairs having a corresponding mirroring resistor coupled in series with a corresponding mirroring transistor, the mirroring resistor of at least one of the mirroring pairs having a serpentine structure.