Sleep Oscillator Switching Circuit for Low Shoot-Through Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low Power Radio Frequency (LPRF) microcontrollers face high sleep current consumption due to 'shoot through current' in existing sleep oscillator circuits, which limits battery life in low duty-cycle applications like battery-powered light sensors.
Innovation Solution
A switching circuit with a control circuit and an output circuit, utilizing series-connected transistor switches and current sources to minimize shoot-through current, featuring a delay mechanism with a capacitor to control the switching stages and ensure efficient edge transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the width of devices in Inverter 2 is increased to improve output edge speed, then the drive current increases, but the parasitic capacitance at the input increases causing larger shoot through current
Solution Approach 1:
The control circuit generates control signals in advance that pre-charge or pre-discharge the parasitic capacitance at the input of Inverter 2 before the main switching event. This preliminary action ensures that when the output transistors switch, the capacitance is already in a favorable state, reducing the shoot through current while maintaining fast edge transitions.
Solution Approach 2:
The control circuit acts as an intermediary between the input signal and the output circuit. It processes the input signal and generates optimized control signals that coordinate the switching of multiple transistors, ensuring that they switch in a sequence that minimizes simultaneous conduction and reduces shoot through current while maintaining drive strength.
2Speed
If a chain of inverter stages is used to sharpen signal edges, then the output edge speed improves, but the average current increases due to multiple shoot through events
Solution Approach 1:
The control circuit merges the control of multiple transistor switches into a coordinated system. Instead of having independent inverter stages each contributing to current consumption, the control circuit synchronizes their operation so that they work together as a unified system, reducing the total average current while achieving the same edge sharpening effect.
Solution Approach 2:
The control circuit implements periodic control signals that rhythmically manage the switching states of the transistors. This periodic action ensures that shoot through current occurs only at specific, minimized intervals rather than continuously, reducing the average current consumption while maintaining the edge sharpening function.
3Speed
If transistor devices are made larger to enable faster switching, then the edge transition speed improves, but the parasitic capacitance increases leading to higher current requirements
Solution Approach 1:
The control circuit performs preliminary charging or discharging of the parasitic capacitance associated with larger transistor devices before they need to switch. This advance preparation reduces the instantaneous current burden during switching events, allowing larger devices to be used for faster edges without proportionally increasing the current requirements.
Data Source
AI summary
A switching circuit suitable for a low power oscillator circuit includes control and output circuits, the control circuit arranged to control the output circuit, the control circuit having input and output terminals, the output circuit having input and output terminals and control terminals; wherein the input terminal of the control circuit is connected to the input terminal of the output circuit, and the control terminal of the output circuit is connected to the output terminal of the control circuit, the output circuit first switches connected in series and arranged such that in use at least one of the switches is in a low impedance state at any given time, and the control circuit has second switches connected in series and arranged such that in use at least one of the switches is in a low impedance state at any given time.