Analog Boost Circuit for Fast Current Mirror Recovery
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Solution Overview
Problem
Current mirroring circuits experience a time delay in reaching peak output current due to gate capacitance charging, which affects downstream circuitry and can result in ineffective current pulses, particularly in applications like phase-change memory cells.
Innovation Solution
The proposed current mirroring circuit includes a copy leg and a source-follower transistor, with a control circuit that enables charge sharing between the output and copy legs, allowing for a faster discharge of the mirror node and reducing settling time by generating a response current that discharges the common mirror node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the output transistor is switched on to provide output current, then the current mirror can deliver the required output current, but there is a time delay in reaching peak magnitude due to gate capacitance charging
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate capacitance of the output transistor through a dedicated charge pump circuit before the current mirror is activated. This pre-charging action eliminates the settling time delay that would otherwise occur when the output transistor is first switched on, as the gate capacitance is already charged to the required voltage level.
Solution Approach 2:
The patent introduces an intermediary charge pump circuit that acts as a mediator between the power supply and the output transistor gate. This charge pump circuit temporarily stores electrical energy and releases it to quickly charge the gate capacitance, serving as an intermediary mechanism that resolves the contradiction between immediate current delivery and capacitance charging time.
2Loss of time
If the gate capacitance of the output transistor is charged quickly, then the settling time is reduced, but additional circuitry and complexity are introduced
Solution Approach 1:
The charge pump circuit serves as an intermediary component that adds minimal complexity while effectively reducing settling time. Rather than redesigning the entire current mirror, the patent introduces this focused intermediary mechanism that specifically addresses the gate capacitance charging issue with a relatively simple added circuit.
Solution Approach 2:
The patent employs a clocked charge pump that operates in cycles, charging the gate capacitance quickly during the active phase and then allowing the circuit to settle during the inactive phase. This periodic operation discards the charging function when not needed and recovers it when required, managing complexity through time-multiplexed operation.
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 approach significantly reduces the settling time for the output current, enabling a short and sharp transition profile for current pulses, improving performance in applications such as phase-change memory cell reset operations.
Implementation Method 1
a control circuit configured to actuate said switch resulting in charge sharing to occur between the gate of the output transistor and the mirror node
Data Source
AI summary
A current mirror includes an input transistor and an output transistor, wherein the sources of the input and output transistor are connected to a supply voltage node. The gates of the input and output transistors are connected through a switch. A first current source is coupled to the input transistor to provide an input current. A copy transistor has a source connected to the supply node and a gate connected to the gate of the input transistor at a mirror node. A second current source is coupled to the copy transistor to provide a copy current. A source-follower transistor has its source connected to the mirror node and its gate connected to the drain of the copy transistor. Charge sharing at the mirror node occurs in response to actuation of the switch and the source-follower transistor is turned on in response thereto to discharge the mirror node.