Current-Controlled Fixed Delay Circuit for PVT Stability
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Solution Overview
Problem
Existing PVT-independent fixed delay circuits are sensitive to variations in voltage, temperature, and process, leading to accuracy and stability issues due to their dependence on special materials and complex reference voltage circuits.
Innovation Solution
A PVT-independent fixed delay circuit using a current generator to produce reference voltages for PMOS and NMOS transistors, with correlative compensation to stabilize delay time, independent of power source voltage and temperature variations, by controlling charging and discharging currents through a structurally simple current generator circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a bandgap reference voltage circuit with operational amplifier and special material resistor is used to control gate voltage, then temperature and process stability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts and eliminates the complex bandgap reference voltage circuit, operational amplifier, and special material resistor from the delay circuit. Instead, it uses a simple current generator with basic transistors and resistors to achieve PVT independence, thereby reducing device complexity while maintaining stability.
Solution Approach 2:
The patent changes the control parameter from gate voltage (requiring complex bandgap reference) to drain current (achievable with simple current generator). By controlling the drain current of transistors M5 and M8 through a simple current generator, the delay time becomes PVT-independent without requiring complex voltage reference circuits.
2Temperature
If special material resistors and bandgap reference circuits are used, then temperature independence is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent replaces expensive special material resistors with ordinary resistors that have standard temperature coefficients. By using common components with known characteristics and designing the current generator to compensate for temperature variations, the circuit achieves temperature independence while being much easier and cheaper to manufacture.
Solution Approach 2:
The patent introduces a current generator as an intermediary circuit that uses ordinary resistors and transistors to generate temperature-compensated control currents. This intermediary converts the temperature coefficients of ordinary resistors into beneficial temperature compensation effects, eliminating the need for special material resistors.
3Loss of time
If inverters are connected in series to provide time delay, then delay function is achieved, but sensitivity to voltage, temperature and process variations increases
Solution Approach 1:
The patent implements implicit feedback by using the same current generator to control both the charging and discharging currents of the inverter chain. The current generator is designed to produce PVT-independent currents, which automatically compensate for variations in the inverter delay, thereby improving reliability without requiring explicit feedback circuits.
Solution Approach 2:
The patent changes the control mechanism from voltage control to current control. By controlling the drain currents of the switching transistors in the inverter chain through a PVT-independent current generator, the delay time becomes insensitive to voltage, temperature, and process variations, thereby improving reliability.
4Ease of manufacture
If current generator uses ordinary resistors with temperature coefficients, then ease of manufacture is improved, but temperature stability deteriorates
Solution Approach 1:
The patent converts the harmful temperature coefficient of ordinary resistors into a beneficial compensation mechanism. By designing the current generator such that the temperature-induced current variations in one transistor compensate for the temperature-induced delay increases in the inverter chain, the circuit achieves temperature stability using ordinary resistors.
Solution Approach 2:
The patent creates a composite current generator circuit that combines multiple transistors and resistors with different temperature characteristics. The overall circuit is designed so that the temperature coefficients of individual components cancel each other out, resulting in a PVT-independent control current that maintains temperature stability.
Data Source
AI summary
A PVT-independent fixed delay circuit includes a circuit structure that has a current generator and a multi-level inverter-based time delay unit. The inverter-based time delay unit has at least two NMOS transistors M5, M6, and at least two PMOS transistors M7, M8. The current generator has a circuit structure including at least two NMOS transistors M1, M2, at least two PMOS transistors M3, M4 and a resistor RS.