Reference Resistor Impedance Scaling With Low Parasitic Capacitance
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Solution Overview
Problem
Existing solutions for achieving high impedance values greater than or equal to 1 MΩ in continuous time are limited by excessive parasitic capacitance, voltage dynamic range, and noise density, while discrete-time resistive devices introduce switching noise, and other electronic devices fail to meet the requirements of large R value, low parasitic capacitance, and high voltage swing.
Innovation Solution
An electronic device modifies the impedance value of a reference resistor by applying a second current that is a fraction of the first current, using current mirrors to achieve a multiplicative factor, allowing for high impedance values with low parasitic capacitance and good linearity, and incorporating FET transistors and voltage divider bridges to enhance impedance transformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If integrated physical resistors are used to achieve high impedance values, then the impedance value increases, but the parasitic capacitance becomes excessive
Solution Approach 1:
The patent uses a current mirror circuit to create a scaled copy of the reference current, which indirectly produces the high impedance effect without requiring a physically large resistor. The current mirror replicates and scales the reference current by a factor K, creating an equivalent high impedance behavior at the output while maintaining low parasitic capacitance characteristics of the reference resistor.
Solution Approach 2:
The patent replaces the physical mechanical resistor structure with an electronic current mirror system. Instead of using a large physical resistor that inherently has high parasitic capacitance, the invention uses active electronic components (transistors in current mirror configuration) to synthesize the high impedance effect through current scaling, thereby eliminating the parasitic capacitance problem associated with large physical resistors.
2Measurement precision
If discrete-time resistive devices are used to achieve high impedance values, then the impedance value increases, but switching noise becomes excessive
Solution Approach 1:
The patent implements a continuous-time operation mode where the current mirror circuit continuously tracks and scales the reference current without discrete switching actions. This continuous operation eliminates the switching noise inherent in discrete-time resistive devices while maintaining the high impedance characteristic, as the current scaling is achieved through continuous transistor operation rather than periodic switching.
3Measurement precision
If other electronic devices are used to achieve high impedance values, then the impedance value increases, but voltage dynamics become limited
Solution Approach 1:
The current mirror circuit serves multiple functions simultaneously: it provides high impedance transformation, maintains wide voltage dynamics by operating with the reference resistor, enables continuous-time operation, and achieves low noise performance. The universal applicability of the current mirror architecture allows it to handle various voltage conditions while maintaining its impedance transformation function, making it more versatile than other specialized high-impedance devices.
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
The device achieves impedance values up to 1 GΩ with low parasitic capacitance, high voltage dynamics, and thermal noise equivalent to physical resistors, operating from DC with low temperature sensitivity and noise characteristics suitable for MOS transistors, while maintaining a compact size and low power consumption.
Implementation Method 1
a second circuit configured to carry a second current between the two second terminals, the value of which corresponds to a fraction of that of the first current
Implementation Method 2
a first FET transistor whose source and drain are each connected to one of the two second terminals and whose gate is capable of, or configured to, receive an electrical potential from the second circuit, the value of which depends on that of the first current
Data Source
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AI summary
Electronic device (100) comprising at least: - a reference resistor (105); - two first terminals (102, 104) between which the reference resistor is connected, and two second terminals (106, 108) between which a modified value of the impedance of the reference resistor is intended to be obtained; - a first circuit (110, 112) configured to apply between the two second terminals a voltage substantially equal to that between the two first terminals; - a second circuit (114, 120, 126) configured to circulate between the two second terminals a second current whose value corresponds to a fraction of a first current intended to circulate in the reference resistor between the two first terminals.