Current Mirror Comparator Biasing for Low Power Stability
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Solution Overview
Problem
Existing comparator circuits in semiconductor integrated circuits face challenges in reducing current consumption, especially as power source voltage increases, and have complex configurations that do not effectively manage bias current fluctuations.
Innovation Solution
A comparator circuit design featuring first and second MOSFETs with a common source connection, a tail resistor, and third and fourth MOSFETs connected to a different power source, where the gate of the first MOSFET receives a voltage difference-based input, and a constant voltage device is used to stabilize the bias current, independent of the second power source voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional comparator circuit uses multiple current mirror circuits and resistors to supply bias current, then the circuit can function as a voltage detector, but the current consumption increases and the circuit complexity increases
Solution Approach 1:
The patent extracts and eliminates redundant current mirror circuits and resistors from the conventional comparator design. By removing the first current mirror circuit (PMOSFETs 133, 134) and associated resistors (122), the circuit achieves the same bias current supply function with fewer components, directly reducing current consumption while maintaining voltage detection capability
Solution Approach 2:
The patent makes the remaining current mirror circuit (NMOSFETs 131, 132, 139) perform multiple functions: it supplies bias current to the differential circuit, provides current mirroring for output stage, and maintains proper biasing without requiring separate resistor-based current control circuits, thereby reducing overall component count and power consumption
2Ease of manufacture
If a conventional comparator circuit uses diode-connected MOSFETs with resistors to control bias current, then the bias current can be set, but the bias current becomes sensitive to power source voltage fluctuations
Solution Approach 1:
The patent implements implicit feedback by using the output of the current mirror circuit (NMOSFET 139) to automatically adjust and stabilize the bias current. The current mirror configuration creates a self-regulating system where changes in power source voltage are compensated through the mirror ratio, maintaining stable bias current without requiring explicit feedback components
Solution Approach 2:
The patent uses current copying through the current mirror mechanism where the bias current established by NMOSFETs 131 and 132 is copied to NMOSFET 139 and subsequently to the differential circuit. This copying mechanism ensures that the bias current remains proportional and stable even when power source voltage fluctuates, as the mirror ratio maintains the current relationship
3Reliability
If a conventional comparator circuit uses multiple current mirror circuits, then proper biasing can be achieved, but the device complexity increases
Solution Approach 1:
The patent merges the functions of multiple current mirror circuits into a single integrated current mirror structure. The NMOSFETs 131, 132, and 139 work together as one unified current mirror system that simultaneously provides bias current to the differential circuit and maintains proper current distribution, eliminating the need for separate PMOSFET-based current mirror and associated control resistors
Solution Approach 2:
The patent segments the circuit into functional blocks where the current mirror circuit (NMOSFETs 131, 132, 139) serves as a standalone bias generation unit that feeds into the differential circuit (PMOSFETs 135, 136 and NMOSFETs 137, 138). This segmentation allows each block to be optimized independently while reducing overall complexity compared to fully interconnected conventional designs
Data Source
AI summary
A comparator circuit can achieve a reduction in current consumption with a simple configuration, and can suppress an increase in current consumption accompanying a rise in power source voltage. A current mirror circuit is connected to a power source, and gates of MOSFETs of the circuit are interconnected. An input signal is applied to a gate of an NMOSFET of the circuit. By determining the value of the signal with a constant voltage device, the voltage across a tail resistor is constant, even in the event that the power source voltage and the input signal change.