Crystal Oscillator Gain Control for Stable Startup and Low Power
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Solution Overview
Problem
Crystal oscillators face instability in oscillation frequency due to changes in external crystal parameters and ambient temperature, leading to issues with startup and high power consumption, as they require an optimal direct current operating point that is difficult to maintain.
Innovation Solution
An oscillator circuit with a gain control circuit that includes a differential amplifier, current source, feedback path, and current mirror, which detects oscillation amplitude and adjusts the operating current through negative feedback to maintain a stable oscillation amplitude, reducing the influence of nonlinearity and ensuring a stable output frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large bias current is used in the crystal oscillator, then the oscillation can start reliably, but the power consumption increases
Solution Approach 1:
The patent implements a dynamic bias current adjustment mechanism where the bias current is automatically modified based on the oscillation state. During startup, a larger bias current ensures reliable oscillation initiation, while after startup, the bias current is reduced to lower power consumption. This dynamic adaptation resolves the contradiction between startup reliability and power consumption by allowing the system to operate in different current states at different times.
Solution Approach 2:
The patent employs a feedback mechanism that monitors the oscillation state and adjusts the bias current accordingly. The feedback loop detects whether the oscillator has successfully started and uses this information to control the bias current magnitude. This feedback-based control enables the system to maintain high startup reliability while minimizing power consumption during normal operation, effectively resolving the contradiction.
2Use of energy by moving object
If a small bias current is used in the crystal oscillator, then the power consumption is reduced, but the oscillation may not start
Solution Approach 1:
The patent applies preliminary action by providing a larger bias current during the startup phase before switching to a smaller current for normal operation. This preliminary high-current state ensures that the oscillation starts reliably, and only after successful startup does the system transition to the lower power consumption state. This temporal separation of current levels resolves the contradiction between power consumption and startup reliability.
Solution Approach 2:
The system dynamically adjusts the bias current based on the oscillation startup status. During the startup phase, the bias current is automatically increased to ensure reliable oscillation initiation. Once startup is confirmed, the bias current is dynamically reduced to minimize power consumption. This dynamic current adjustment resolves the contradiction by allowing the system to have high reliability during startup and low power consumption during operation.
3Device complexity
If the operating point is fixed in the crystal oscillator, then the circuit is simple, but the output frequency becomes unstable due to temperature and crystal parameter changes
Solution Approach 1:
The patent implements a feedback mechanism that monitors the oscillation frequency and adjusts the operating point to compensate for temperature and crystal parameter changes. The feedback loop detects frequency deviations caused by environmental variations and automatically modifies the bias conditions to restore the optimal operating point. This feedback-based operating point adjustment resolves the contradiction by maintaining frequency stability without requiring a completely complex circuit redesign.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the bias current and voltage levels in response to temperature and crystal parameter variations. Instead of fixing the operating point, the system modifies key electrical parameters (current, voltage) to track the optimal operating conditions under different environmental conditions. This parameter adaptation resolves the contradiction between circuit simplicity and frequency stability by using controlled parameter variations.
Data Source
AI summary
An oscillator circuit is provided and includes first and second terminals; an amplification circuit with an input end and an out end coupled to a first end and a second end of a crystal circuit through the first terminal and the second terminal, respectively; a gain control circuit coupled to the amplification circuit and including a differential amplifier, a first current source, a feedback path and a current mirror, wherein: the differential amplifier includes first and second transistors, sources of the first and second transistors are coupled to the first current source; a gate of the first transistor is coupled to a first direct current voltage and coupled to the input end or the output end through the feedback path; a gate of the second transistor is coupled to a second direct current voltage; the current mirror mirrors a current flowing through the second transistor to the amplification circuit.