Differential Crystal Oscillator Circuit to Prevent High-Gain Latching
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Solution Overview
Problem
Existing differential crystal oscillator circuits face issues with latching at high loop gain frequencies, amplitude regulation difficulties, and significant spread in active load characteristics, which affect stability and operation at low supply voltages.
Innovation Solution
A differential crystal oscillator circuit design incorporating a current source and differential amplifier with cross-coupled transistors, low pass, and high pass filters, using current sources as an active load to achieve high loop gain and common mode rejection, eliminating the need for a special active load and allowing operation at low supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional active load is used in differential crystal oscillator circuits, then the circuit can operate, but it exhibits significant spread in characteristics and causes latching at high loop gain frequencies
Solution Approach 1:
The patent removes the traditional active load component from the oscillator circuit and replaces it with a current source. This extraction of the problematic active load eliminates the latching condition and characteristic spread while maintaining the necessary oscillation function through the differential amplifier configuration.
Solution Approach 2:
The patent changes the load impedance parameter from an active load with varying characteristics to a current source with stable, predictable characteristics. This parameter change from voltage-controlled to current-controlled loading stabilizes the loop gain and prevents latching conditions across different operating conditions.
2Reliability
If high loop gain is achieved for stable oscillation, then oscillation stability improves, but latching conditions occur at high loop gain frequencies
Solution Approach 1:
The patent employs feedback through the differential amplifier configuration with cross-coupled transistors to maintain stable oscillation. The feedback mechanism ensures that high loop gain is achieved at the desired oscillation frequency while the current source loading prevents the latching condition that would otherwise occur at high loop gain frequencies.
3Device complexity
If traditional active load characteristics are used, then the circuit design is simpler, but there is significant spread in load characteristics affecting stability
Solution Approach 1:
The current source is designed to automatically provide stable loading characteristics without requiring complex compensation circuits. The self-biasing nature of the current source eliminates the need for additional components to stabilize the load characteristics, maintaining circuit simplicity while achieving consistent performance.
4Use of energy by moving object
If low supply voltage is used, then power consumption is reduced, but the circuit requires special active loads that cause uncontrolled DC paths
Solution Approach 1:
The patent removes the special active load component that creates uncontrolled DC paths and replaces it with a current source configuration. This extraction allows the circuit to operate at low supply voltages while maintaining controlled DC current paths through the differential amplifier and current source combination.
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 solution provides stable oscillations, avoids latching conditions, achieves superior ripple and supply noise rejection, and suppresses parasitic oscillations, enabling operation at low supply voltages without uncontrolled DC paths.
Implementation Method 1
The differential crystal oscillator includes a current source. A differential amplifier is included to excite the resonance element. The differential amplifier is coupled to the current source
Implementation Method 2
The crystal oscillator circuit sustains oscillation by taking a voltage signal from the quartz resonator, amplifying it, and feeding it back to the resonator
Implementation Method 3
A crystal oscillator, particularly one using a quartz crystal, works by distorting the crystal with an electric field, when voltage is applied to an electrode near or on the crystal. This property is known as electrostriction or inverse piezoelectricity
Implementation Method 4
When the field is removed, the quartz—which oscillates in a precise frequency—generates an electric field as it returns to its previous shape, and this can generate a voltage
Implementation Method 5
The differential crystal oscillator circuit further includes a low pass filter and a high pass filter
Data Source
AI summary
A differential crystal oscillator circuit is disclosed. The differential crystal oscillator circuit includes an output port. The output port includes a first terminal and a second terminal. A resonance port is included to couple a resonance element to the differential crystal oscillator circuit. The differential crystal oscillator includes a current source. A differential amplifier is included to excite the resonance element. The differential amplifier is coupled to the current source and the resonance port. The differential amplifier includes a plurality of transistors. The differential crystal oscillator circuit further includes a low pass filter that in combination with a transistor in the differential amplifier exhibits characteristics of a high pass filter. The differential amplifier is configured to use the current source as an active load.