On-Chip Bias Current Generation Using Triode Transistor Resistance
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Solution Overview
Problem
On-chip bias current generation is affected by process and temperature variations due to internal resistor characteristics, leading to inaccuracies and increased costs when external resistors are used to mitigate these issues.
Innovation Solution
The use of internal components that replicate external resistance characteristics to generate bias currents, such as constant and PTAT currents, reduces the impact of process and temperature variations by employing current mirrors and external resistors, allowing for more accurate and stable current generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an internal resistor is used to generate bias current, then the circuit size and cost are reduced, but the manufacturing precision and temperature stability deteriorate due to process variations causing up to ±30% resistance variation
Solution Approach 1:
The patent uses a transistor device operating in the triode region to replicate the resistance characteristics of an external resistor. By configuring the transistor with specific width-to-length ratios, it copies the resistance value and temperature dependence of the external resistor, allowing the circuit to achieve external-resistor-level precision without actually using an external resistor component.
Solution Approach 2:
The patent changes the operating parameters of the transistor device by controlling its gate voltage to maintain operation in the triode region. This parameter control allows the transistor's resistance to be adjusted and stabilized, compensating for process variations and achieving precise bias current generation that matches external resistor performance.
2Manufacturing precision
If an external resistor is used to reduce resistance variation effects, then the manufacturing precision and temperature stability improve, but the device complexity and circuit size increase due to additional pins and components
Solution Approach 1:
Instead of using an actual external resistor component, the patent creates an internal copy of the resistor's electrical characteristics using a transistor device. This copy replicates both the resistance value and the temperature coefficient, providing the same precision benefits without adding physical components or external pins to the circuit.
Solution Approach 2:
The patent merges the resistor function with the transistor device by operating the transistor in its triode region where it exhibits resistive behavior. This combines multiple functions into a single device, eliminating the need for separate resistor components and reducing overall circuit complexity while maintaining precision.
3Ease of manufacture
If internal components are used to replicate external resistance, then the ease of manufacture improves by avoiding external components, but the device complexity increases due to additional circuitry for current mirrors and voltage generation
Solution Approach 1:
The patent merges multiple functions into integrated circuit blocks: the voltage generation circuit, current mirror circuit, and transistor-based resistance replication are combined into a unified bias current generation system. This integration achieves ease of manufacture through full on-chip implementation while managing complexity through functional consolidation rather than separate discrete components.
Solution Approach 2:
The transistor device serves multiple functions: it acts as an active element for current generation, functions as a voltage-controlled resistor to replicate external resistance characteristics, and provides temperature compensation. This multi-functionality reduces the need for separate dedicated components, balancing integration benefits against architectural complexity.
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
This approach results in bias currents that are less dependent on manufacturing process and temperature variations, improving accuracy and reducing the need for additional circuit components, thereby minimizing cost and size increases.
Implementation Method 1
a first transistor device coupled to a second transistor device, where the second transistor device is maintained in a triode region
Implementation Method 2
a current mirror circuit coupled to the external resistor and the first transistor device, the current mirror circuit comprising a third transistor device and a fourth transistor device
Implementation Method 3
an internal voltage (Vbg) which is independent of temperature can be generated using a bandgap circuit
Implementation Method 4
the difference in the base to emitter voltages of the two PNP BJTs (e.g., P1 and P2) is proportional to the temperature of the circuit
Data Source
AI summary
Bias current generation circuits and systems are disclosed. In one embodiment, a bias current generation system comprises a current generation circuit generating a first current based on a first voltage and an external resistor, a current mirror forwarding a second current proportional to the first current, and one or more bias current generation circuits with each circuit generating a bias current based on a second voltage over a resistance of a transistor device, where the transistor device is maintained in a triode region using a third voltage associated with the second current and where the resistance of the transistor device shares characteristics of a resistance of the external resistor.