gm-cell transconductance calibration via external resistor feedback
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Solution Overview
Problem
Transconductance in gm-cell based circuitry is not consistently controlled against temperature and process corners, and on-chip resistors may not be accurately controlled, leading to variability in circuit performance.
Innovation Solution
Implementing a gm-cell with negative feedback circuitry to adjust transconductance proportionally to a variable resistor, and providing calibration circuitry to determine the value of the resistor using an external resistor with a known accurate value, ensuring constant transconductance across temperature and process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If on-chip resistors are used in gm-cell based circuitry, then device integration is improved, but manufacturing precision deteriorates due to inaccurate value control
Solution Approach 1:
The patent employs feedback mechanisms where the gm-cell circuitry senses the actual transconductance value and adjusts control signals to compensate for resistor value deviations. This closed-loop approach allows the system to maintain accurate transconductance control despite variations in on-chip resistor values during manufacturing.
Solution Approach 2:
The patent utilizes adjustable control parameters (such as bias voltages or currents) that can be dynamically modified to compensate for fixed resistor value variations. By changing operational parameters rather than physical dimensions, the system achieves precise transconductance control while maintaining integrated on-chip resistor implementation.
2Use of energy by moving object
If gm-cell based circuitry is designed for low power consumption, then energy efficiency is improved, but reliability deteriorates due to temperature and process corner variability
Solution Approach 1:
The patent implements feedback circuits that continuously monitor transconductance variations caused by temperature and process corners, and automatically adjust control signals to maintain consistent performance. This feedback mechanism enables low-power operation without sacrificing reliability, as the system compensates for environmental variations dynamically rather than requiring over-designed margins.
Solution Approach 2:
The gm-cell based circuitry incorporates self-calibration and self-adjustment capabilities that allow it to automatically compensate for temperature and process variations without external intervention. The circuit monitors its own performance and makes real-time corrections, enabling reliable low-power operation across varying conditions.
3Manufacturing precision
If transconductance is made controllable to compensate for resistor variations, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent uses feedback control circuits that, while adding some complexity, provide automated compensation for resistor variations. The feedback mechanism replaces the need for extremely precise resistor manufacturing with a more manageable control system that can tolerate standard manufacturing variations while achieving the desired transconductance precision.
Solution Approach 2:
The patent achieves precise transconductance control by adjusting electrical parameters (voltages, currents) rather than physical dimensions. This approach shifts the complexity from precision manufacturing to parameter control, which can be accomplished through standard CMOS circuit techniques and requires less stringent fabrication processes.
4Manufacturing precision
If calibration circuitry is added to correct on-chip resistor values, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent integrates calibration and compensation functions directly into the existing gm-cell operational circuitry rather than adding separate dedicated calibration components. The same control signals and feedback paths used for normal operation are leveraged for calibration purposes, reducing the need for additional discrete components and minimizing the increase in device complexity.
Solution Approach 2:
The control circuitry in the patent serves multiple functions: it controls transconductance during normal operation and simultaneously performs calibration and compensation for resistor variations. This multi-functional approach eliminates the need for separate calibration circuits, achieving high manufacturing precision while keeping the overall device complexity manageable through functional consolidation.
Data Source
AI summary
Transconductance (gm)-cell based circuitry is well suited for low power, low voltage complementary metal oxide silicon (CMOS) design in deep sub micro technology. This circuitry includes a gm cell as the basic building block. As such, it is desirable to have the transconductance of the gm cell to be constant against temperature and process corners. The present disclosure describes various gm-cell based circuitry having a controllable transconductance. Preferably, the controllable transconductance can be selectively controlled to be equal to the inverse of the value of an on-chip resistor. For example, the gm-cell based circuitry can sense the transconductance of an internal replica unit and can use negative feedback circuitry to cause this transconductance to be approximately equal a value of an on-chip resistor. However, in some situations, a value of this on-chip resistor is not accurately controlled. Therefore, the present disclosure also discloses a manner of calibrating the gm-cell based circuitry against an external resistor with a known accurate value.