PTAT-Biased CMOS Crystal Oscillator for Radiation and Temperature Stability
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Solution Overview
Problem
Current crystal stabilized clock sources are not adequately radiation hardened, particularly for space environments, and are temperature sensitive, leading to performance degradation and challenges in instrument design for space applications.
Innovation Solution
A Radiation Hardened By Design (RHBD) high frequency crystal stabilized oscillator using a comparator with PTAT PMOS and NMOS bias inputs, coupled with a resonator and feedback resistor, to maintain gain and frequency stability over temperature and radiation exposure, and a duty cycle adjustment mechanism to compensate for radiation-induced input offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional CMOS crystal stabilized oscillator is used, then the device can operate at standard temperatures, but it suffers from excessive leakage currents and threshold voltage changes under total ionizing dose radiation, leading to severe functionality degradation
Solution Approach 1:
The patent modifies the CMOS oscillator circuit parameters by introducing radiation-hardened transistor configurations and biasing schemes that change the electrical characteristics to resist radiation-induced leakage and threshold shifts, maintaining functionality under TID exposure while remaining compatible with standard CMOS manufacturing processes
Solution Approach 2:
The patent creates a replicated version of the conventional CMOS oscillator that incorporates radiation hardening techniques, effectively copying the basic oscillator architecture while modifying specific components to achieve radiation resistance without requiring entirely new manufacturing processes
2Reliability
If spot-shielding or vault enclosure is used to protect COTS clock sources, then radiation immunity can be achieved, but the device mass and complexity increase significantly
Solution Approach 1:
The patent extracts the radiation hardening requirements from the external shielding approach and implements them directly within the CMOS oscillator circuit itself, removing the need for additional mass-based protection while maintaining radiation immunity
Solution Approach 2:
The patent replaces the mechanical/physical shielding system (spot-shielding or vault enclosure) with an electronic/circuit-based solution implemented at the transistor level, substituting mass-dependent protection with circuit topology and biasing that provides radiation hardness without additional mass
3Temperature
If the oscillator amplifier gain and speed are allowed to change with temperature, then the circuit can operate across a wide temperature range, but the frequency stability and performance degradation occur
Solution Approach 1:
The patent implements feedback mechanisms within the oscillator circuit that automatically adjust amplifier gain and bias conditions in response to temperature changes, maintaining frequency stability across a wide operating temperature range by counteracting temperature-induced parameter drift
Solution Approach 2:
The patent introduces dynamic biasing and gain control mechanisms that adapt the oscillator circuit parameters in real-time according to temperature conditions, allowing the circuit to maintain stable frequency performance across varying temperatures by continuously adjusting operating points
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 RHBD clock source provides enhanced Total Ionizing Dose immunity and temperature stability, allowing for local clock signal generation and data transmission without requiring a separate synchronization signal, reducing mass and power requirements and improving data integrity in harsh environments.
Implementation Method 1
a resonator element and feedback resistor coupled between the comparator output and the negative comparator input to generate a waveform with a user determined gain and frequency at the comparator output
Implementation Method 2
The resonator may include an inductor-capacitor (LC) tank circuit or a piezo-electric crystal
Data Source
AI summary
A clock source includes a comparator having a positive comparator input, a negative comparator input, a proportional to absolute temperature (PTAT) PMOS bias input, a PTAT NMOS bias input, and a comparator output, a resonator element, series and feedback resistors and other passive components coupled between the comparator output and the negative comparator input to generate a signal with approximately constant gain and frequency at the comparator output, and a PTAT bias circuit coupled to the comparator's PTAT PMOS and NMOS bias inputs, and configured to drive the PTAT PMOS bias input and the PTAT NMOS bias input to maintain approximately constant gain and frequency over the operating temperature range of the clock source.