Transistor Matching for Precise Current Ratios
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Solution Overview
Problem
Bipolar transistor temperature transducers in integrated circuits face inaccuracies in temperature measurement due to slight variations in matched transistors, leading to deviations in current ratios, which are costly to mitigate through increased transistor size or complex random dynamic element matching methods.
Innovation Solution
A current driver system with a control logic circuit that periodically switches on and off multiple transistors in a current generation cycle, ensuring each switch is activated an equal number of times to average out matching errors and maintain accurate current ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of matched transistors is increased to improve current ratio accuracy, then measurement precision is improved, but device area and manufacturing cost increase significantly
Solution Approach 1:
The patent divides a single large transistor into multiple smaller transistors (e.g., four transistors instead of one). By segmenting the transistor array and using dynamic switching among them, the system achieves the current ratio accuracy that would otherwise require a much larger single transistor, while keeping the total area manageable.
Solution Approach 2:
The patent employs dynamic element matching by periodically switching different transistor combinations into the circuit during operation. This dynamic switching allows the system to average out matching errors across multiple transistor samples, achieving high measurement precision without requiring each individual transistor to be perfectly matched or excessively large.
2Measurement precision
If random dynamic element matching is used to improve current ratio accuracy, then measurement precision is improved, but design complexity and measurement cycle time increase
Solution Approach 1:
The patent implements periodic switching of transistor combinations in a systematic sequence. Rather than using complex random switching, the system cycles through predetermined transistor groupings in a regular pattern, which simplifies the control logic while still achieving the benefit of dynamic element matching by sampling multiple transistor combinations over time.
3Manufacturing precision
If transistor size is increased to reduce matching variations, then manufacturing precision is improved, but device area and cost increase prohibitively
Solution Approach 1:
The patent segments the transistor function across multiple smaller devices rather than relying on a single large transistor. This segmentation allows the system to achieve the effective matching precision of a large transistor by using statistical averaging across multiple smaller, more area-efficient devices.
Solution Approach 2:
The patent creates multiple copies of smaller transistor units instead of one large transistor. By using multiple identical or similar-sized transistor copies and dynamically switching among them, the system achieves the performance characteristics of a much larger transistor while maintaining a compact layout and reducing overall silicon area requirements.
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 effectively cancels out matching errors across multiple frames, providing accurate current ratios and improving the precision of temperature measurements in bipolar transistor temperature transducers without the need for large transistor sizes or increased design complexity.
Implementation Method 1
A current driver system with a control logic circuit that periodically switches on and off multiple transistors in a current generation cycle, ensuring each switch is activated an equal number of times to average out matching errors
Implementation Method 2
bipolar transistors have an emitter-to-base voltage (Veb) that varies predictably with regard to temperature
Implementation Method 3
a resulting change in emitter-to-base voltage (ΔVeb) is directly proportional to a product of the absolute temperature T and the logarithm of a ratio of the collector currents (IC2/IC1)
Data Source
AI summary
Systems and methods are provided for generating accurate current ratios from a current mirror including an array of output transistor and a corresponding array of switches. Each switch couples in series with its corresponding output transistor. A control logic circuit controls the switches to cancel mismatches for the output transistors.