Current-Mirror Oscillator for Stable CMOS Frequency Output
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Solution Overview
Problem
Conventional integrated circuit oscillators, such as ring oscillators, are sensitive to temperature variations and power supply changes, leading to unstable frequency output, and existing solutions like bandgap reference-based oscillators consume significant power and occupy large silicon area.
Innovation Solution
A current-mode oscillator circuit with a delay generation circuit using current mirrors, capacitive, and resistive elements, where the frequency of oscillation is independent of transistor fabrication processes, power supply variations, and biasing current, relying solely on the values of capacitance and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional ring oscillator circuit is used, then the oscillator can be easily fabricated in integrated circuits, but the frequency output is strongly dependent on temperature and power supply variations
Solution Approach 1:
The patent changes the operating parameters of the oscillator by using a current mirror configuration where the oscillation frequency is determined by the ratio of currents in parallel branches rather than by absolute current values or RC time constants. This parameter transformation makes the frequency independent of power supply variations and temperature-dependent resistance changes, as the current ratios remain stable despite environmental variations
Solution Approach 2:
The patent replaces the traditional RC timing mechanism with a current-mode operation using MOS transistors in saturation region. Instead of relying on resistive charging of capacitors (which is temperature-sensitive), the invention uses controlled current sources and mirrors to charge capacitive nodes, substituting the mechanical/resistive timing approach with an electronic current-controlled approach that is much more stable against temperature and supply variations
2Reliability
If a bandgap reference-based oscillator is used, then the frequency stability against temperature and power supply variations is improved, but the power consumption and silicon area increase significantly
Solution Approach 1:
The patent extracts and eliminates the complex bandgap reference circuitry from the oscillator design. By using a simpler current mirror-based approach where the oscillation frequency depends on current ratios rather than absolute reference voltages, the invention removes the need for temperature-compensated bandgap references, thereby significantly reducing power consumption and silicon area while maintaining frequency stability
Solution Approach 2:
The patent uses simple, readily available MOS transistors in standard CMOS technology to create the current mirrors and oscillation circuit, replacing expensive and complex bandgap reference components. The current mirror configuration uses basic transistor pairs that are already present in standard CMOS processes, eliminating the need for additional expensive temperature-stabilized reference circuits
3Reliability
If a bandgap reference-based oscillator is used, then the frequency stability against temperature and power supply variations is improved, but the silicon layout area increases
Solution Approach 1:
The patent merges the functions of current reference generation, temperature compensation, and oscillation into a single integrated current mirror circuit. The same transistors that form the current mirrors also provide the oscillation mechanism, eliminating the need for separate bandgap reference circuits and reducing the overall silicon area required for the oscillator
4Speed
If the supply voltage VCC is increased to increase oscillation frequency, then the frequency of oscillation increases, but the circuit becomes more sensitive to power supply variations
Solution Approach 1:
The patent performs preliminary current equalization by using the current mirror to pre-establish equal currents in parallel branches before oscillation begins. The oscillation frequency is determined by this pre-established current ratio rather than by the absolute supply voltage level, allowing the circuit to operate at various supply voltages without becoming sensitive to power supply variations
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 proposed oscillator achieves a frequency output that is stable and independent of temperature and power supply variations, with low power consumption and minimal layout area, maintaining consistency across different fabrication processes and voltage conditions.
Implementation Method 1
a capacitive element coupled to the first current mirror branch
Implementation Method 2
a resistive element coupled to the second current mirror branch
Data Source
AI summary
An oscillator circuit for use in integrated circuits. The oscillator circuit includes a delay generation circuit having a current mirror with at least a first current mirror branch and a second current mirror branch, a current source coupled to the first current mirror branch, a capacitive element coupled to the first current mirror branch; and a resistive element coupled to the second current mirror branch. The oscillator circuit further includes a plurality of inverting elements coupled in series with one another and a transconducting element coupled to an output of the plurality of inverting elements. The transconducting element is configured to discharge the capacitive element. A latching element is coupled to latch to an output signal of the plurality of inverting elements.