Low-Leakage Current Source Circuit Design
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Solution Overview
Problem
As CMOS technology scales smaller, leakage current increases significantly, impacting the performance of circuits like phase lock loops and digital-to-analog converters, and existing solutions such as high threshold voltage transistors or larger transistor sizes are inadequate for reducing leakage current without compromising circuit speed.
Innovation Solution
A low-leakage current source circuit design using three transistors, where the second and third transistors enable or isolate the first transistor to manage its threshold voltage, reducing leakage current by manipulating gate and source voltages, and this design can be integrated into current mirrors and amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistor size is reduced to enable more transistors on IC die and faster operating speed, then circuit integration and speed are improved, but leakage current increases significantly
Solution Approach 1:
The patent segments the control of the main transistor into two independent parts: a first transistor controls the switching function while a second transistor controls the threshold voltage. This segmentation allows independent optimization of switching speed and leakage reduction without compromising overall circuit performance.
Solution Approach 2:
The patent introduces a second transistor as an intermediary element that specifically manages the threshold voltage of the first transistor. This intermediary component enables precise control over leakage current without affecting the switching functionality provided by the first transistor.
2Object-generated harmful factors
If high threshold voltage transistors are used to reduce leakage current, then leakage current is reduced, but circuit speed decreases
Solution Approach 1:
The patent dynamically adjusts the threshold voltage of the first transistor through the second transistor based on operational requirements. During active operation, the threshold voltage is maintained at optimal levels for high-speed switching, while during idle states, the threshold voltage is increased to minimize leakage current.
Solution Approach 2:
The patent changes the threshold voltage parameter of the first transistor dynamically using the second transistor. By modulating the gate voltage of the second transistor, the threshold voltage of the first transistor is adjusted to achieve low leakage current without permanently compromising circuit speed capability.
3Object-generated harmful factors
If larger transistor sizes are used to combat leakage current, then leakage current is marginally reduced, but circuit area increases and effectiveness is limited
Solution Approach 1:
Instead of changing the physical dimensions of the transistor, the patent changes the electrical parameters (threshold voltage) through the second transistor. This approach reduces leakage current effectively without increasing the transistor area, maintaining circuit compactness while achieving the desired leakage reduction.
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
AI summary
A low-leakage circuit includes first, second, and third transistors, which may be P-channel or N-channel FETs. The first transistor provides an output current when enabled and presents low leakage current when disabled. The second transistor enables or disables the first transistor. The third transistor connects or isolates the first transistor to/from a predetermined voltage (e.g., VDD or VSS). The circuit may further include a pass transistor that provides a reference voltage to the source of the first transistor when the first transistor is disabled. In an ON state, the first transistor provides the output current, and the second and third transistors do not impact performance. In an OFF state, the second and third transistors are used to provide appropriate voltages to the first transistor to place it in a low-leakage state. The first, second, and third transistors may be used for a low-leakage current source within a current mirror, an amplifier stage, and so on.