Precharge RC Delay Circuit for PVT-Stable Timing
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Solution Overview
Problem
Delay circuits exhibit significant variations in time delay due to process, voltage, and temperature (PVT) fluctuations, affecting their reliability across different operating conditions.
Innovation Solution
A delay circuit design incorporating a precharge transistor, a resistor with a negative temperature coefficient, a capacitive device, and an inverter, where the precharge and discharge transistors are configured to charge and discharge the capacitive device in response to input signal polarity changes, minimizing PVT variations by using an RC time constant and incorporating a reset switch for operational modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional delay circuit is used, then the circuit structure is simple, but the time delay varies significantly over PVT conditions
Solution Approach 1:
The patent uses a resistor with negative temperature coefficient to counteract the positive temperature coefficient of the capacitor, creating a temperature-compensated RC time constant. This parameter matching approach ensures that the delay time remains stable across temperature variations by having the resistance decrease as temperature increases, offsetting the capacitor's tendency to increase its time constant with temperature
Solution Approach 2:
The precharge transistor charges the capacitive device before the delay operation begins, establishing a known initial voltage state. This preliminary action ensures that the delay circuit starts from a defined condition, improving reproducibility and stability of the delay time across different operating conditions
2Reliability
If the capacitive device is charged through the precharge transistor, then the delay circuit achieves stable delay, but additional transistors are required
Solution Approach 1:
The precharge transistor serves multiple functions: it charges the capacitive device during the precharge phase, acts as a switch to isolate the capacitor during discharge, and helps establish the initial voltage condition. This multi-functionality reduces the need for separate dedicated components, making the added complexity more efficient
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 circuit achieves reduced variation in time delay across PVT conditions, with the negative temperature coefficient resistor counteracting temperature effects, resulting in a more stable delay performance and improved reliability.
Implementation Method 1
The resistor may have a negative temperature coefficient
Implementation Method 2
A capacitive device and the inverter may be coupled to the node
Data Source
AI summary
A delay circuit includes precharge and discharge transistors configured to receive an input signal. The delay circuit also includes a resistor coupled to the precharge transistor having a negative temperature coefficient to thereby form a node. A capacitive device and an inverter are coupled to the node. The inverter produces an output signal. Responsive to the input signal having a first polarity, the precharge transistor is configured to be turned on and the discharge transistor is configured to be turned off to thereby cause current to flow through the precharge transistor to the capacitive device to thereby charge the capacitive device. Responsive to the input signal having a second polarity, the precharge and discharge transistors are configured to change state to thereby cause charge from the capacitive device to discharge through the resistor and through the discharge transistor. The voltage on the node decays to a level which eventually causes the inverter's output to change state.