Controllable Current Source Leakage Compensation
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Solution Overview
Problem
Controllable current sources in integrated circuits suffer from leakage currents that distort output signals and require high supply voltages due to series circuits of transistors, which is problematic in microelectronic circuits trending towards smaller voltages.
Innovation Solution
Incorporating a replica of the current paths connected via a current mirror to the output terminal, which compensates for leakage currents by generating a replicated leakage current difference with the correct sign, allowing for leakage current compensation and operation with lower supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If series circuits of transistors are used to form controllable current paths, then the current source can provide positive or negative output current, but the circuit requires a relatively large supply voltage
Solution Approach 1:
The current source is divided into two independent controllable current paths (first and second current paths), each capable of sourcing current independently. This segmentation allows the circuit to provide bidirectional current output without requiring a large supply voltage, as each path can be controlled separately to achieve the desired current direction.
Solution Approach 2:
The patent employs dynamic control of the current paths through control signals that can switch the current paths on and off or adjust their conduction levels. This dynamic control enables the current source to adapt its output current direction and magnitude in real-time, providing versatility without requiring excessive supply voltage headroom.
2Ease of operation
If controllable current paths are used in a current source, then the output current can be controlled by digital voltage signals, but leakage currents flow even in the switched-out state and distort the output signal
Solution Approach 1:
The patent introduces replica current paths that are identical copies of the original controllable current paths. These replica paths generate leakage currents that mirror the leakage in the original paths. By copying the leakage behavior, the system can compensate for it and maintain output signal accuracy despite the presence of leakage currents during digital control operation.
Solution Approach 2:
The patent implements a feedback mechanism where the leakage currents generated by the replica current paths are used to compensate for leakage in the original current paths. The replica output terminal is connected to the output terminal, creating a feedback loop that automatically adjusts for leakage current distortion, thereby maintaining high output signal accuracy during digital control.
3Reliability
If replica current paths are added to compensate for leakage currents, then the output signal quality improves, but the device complexity increases
Solution Approach 1:
Instead of implementing complex leakage compensation circuits, the patent uses simple replica current paths that are identical copies of the original current paths. This copying approach achieves effective leakage compensation while maintaining relatively simple circuit structure, as the replica paths can be implemented using the same transistor configurations and control logic as the original paths.
Solution Approach 2:
The replica current paths serve multiple functions: they generate leakage currents for compensation, provide a feedback mechanism for accuracy improvement, and can potentially serve as additional controllable current sources. This multi-functionality reduces the need for separate compensation circuits, thereby limiting the increase in device complexity while achieving improved output signal quality.
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 solution improves the quality of the output signal by effectively compensating for leakage currents, enabling operation with lower supply voltages and a larger control range, thereby reducing signal errors and improving the performance of phase locked loops.
Implementation Method 1
a replica output terminal is connected via a current mirror with the output terminal
Data Source
AI summary
The invention concerns a controllable current source or “charge pump” (12) in an integrated circuit, comprising two supply terminals (K1, K2) for the application of two supply potentials (V1, V2) as well as an output terminal (Kout) for the delivery of an output current, connected via a first controllable current path (T1) with the first supply terminal (K1), and via a second controllable current path (T2) with the second supply terminal (K2). In order to improve the current source (12) with regard to the quality of the output signal, it is provided according to the invention that the controllable current source (12) furthermore has a replica (T1′, T2′) of the current paths (T1, T2) in their non-controlled state, of which a replica output terminal (Kout′) is connected via a current mirror (T5 to T8) with the output terminal (Kout).