Switching Current Source Circuit for Fast Settling
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Solution Overview
Problem
Switched-capacitor circuits face challenges with long settling times due to small bias currents or heavy loading, leading to increased static power consumption when using higher bias currents or driving buffers.
Innovation Solution
A switching current source circuit comprising mirror transistors, a switch, capacitors, and a voltage generating unit that selectively provides different voltages to control the bias current and output current, allowing for fast switching without excessive power consumption by adjusting the voltage and transistor connections based on control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a higher bias current is used to reduce settling time, then the settling time is reduced, but the static power consumption is increased
Solution Approach 1:
The patent applies dynamics by making the bias current adjustable rather than fixed. A control circuit dynamically changes the bias current of the operational amplifier based on the switching state: during switching operations, the bias current is increased to reduce settling time; during stable operation, the bias current is reduced to minimize static power consumption. This dynamic adjustment resolves the contradiction between settling time and power consumption.
Solution Approach 2:
The patent changes the parameter of bias current from a constant value to a variable value that adapts to different operating conditions. By using control signals to modulate the bias current magnitude, the system optimizes both settling time and power consumption depending on the operational phase, directly addressing the technical contradiction.
2Loss of time
If a driving buffer is added to reduce settling time, then the settling time is reduced, but the device complexity is increased
Solution Approach 1:
Instead of always providing maximum driving capability through a dedicated buffer, the patent applies partial action by selectively enhancing the driving capability only when needed during switching transitions. The operational amplifier's bias current is temporarily increased to provide excessive driving capability during critical switching moments, then reduced to normal levels otherwise, avoiding the need for a permanent buffer structure.
Data Source
AI summary
A switching current source circuit is provided. A current source drains a bias current from a power supply via a first mirror transistor. A second mirror transistor has a source coupled to the power supply, a gate coupled to the gate of the first mirror transistor, and a drain for providing an output current. A switch is coupled between the gates of the first and second mirror transistors, and has a control terminal for receiving a control signal. A first capacitor is coupled between the gate of the second mirror transistor and the voltage generating unit. A second capacitor is coupled between the gate of the second mirror transistor and a ground. The voltage generating unit selectively provides a first voltage or a second voltage different from the first voltage to the first capacitor according to the control signal.