Oscillation Frequency Control Circuit for Stable Free-Running Operation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional oscillation frequency control circuits face challenges in maintaining stable frequency when a highly stable reference signal is not input, leading to excessive frequency deviation due to aging, especially in long-term operations, and require frequent correction, which is cumbersome.
Innovation Solution
An oscillation frequency control circuit with a voltage-controlled oscillator, phase comparator, loop filter, detection circuit, pulse generation circuit, memory for storing control voltage information, and a control unit that adjusts the connection between components to use either an external reference signal or a variable control voltage, allowing for frequency correction and stable operation even without a stable reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oscillation frequency control circuits operate without a highly stable reference signal, then the circuit can function in free-running mode, but frequency deviation increases excessively due to aging
Solution Approach 1:
The patent applies preliminary action by measuring and storing the actual oscillation frequency during periods when a stable reference signal is available. The correction value calculated from the difference between the measured frequency and the reference frequency is stored in advance in a correction value storage unit. When the reference signal becomes unavailable, this pre-stored correction value is applied to compensate for frequency drift due to aging, eliminating the need for frequent manual corrections and maintaining frequency stability over long periods.
2Reliability
If frequent frequency corrections are performed manually, then frequency stability can be maintained, but the operation becomes cumbersome and time-consuming
Solution Approach 1:
The patent implements self-service through an automatic frequency correction system. The measurement unit automatically measures the oscillation frequency, the correction value calculation unit automatically calculates the deviation from the reference frequency, and the correction value storage unit automatically stores and applies correction values. This automated process eliminates the need for manual frequency measurement and adjustment operations, allowing the system to maintain frequency stability autonomously over long periods without user intervention.
3Measurement precision
If a highly stable reference signal is always available, then frequency accuracy is maintained, but the system cannot operate independently when the reference signal is interrupted
Solution Approach 1:
The system performs preliminary measurement and storage of frequency characteristics during periods when the highly stable reference signal is available. The measurement unit captures the actual oscillation frequency and stores it alongside the reference frequency. This pre-stored data enables the system to calculate correction values and maintain accurate frequency operation independently when the reference signal is interrupted, combining the benefits of reference-signal-locked accuracy with independent operation capability.
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 circuit effectively corrects its own frequency and maintains stability by using stored control voltage information and pulse generation data, reducing frequency deviation and eliminating the need for frequent corrections, thus ensuring reliable operation over time.
Implementation Method 1
a voltage controlled crystal oscillator (VCXO) 35 configured to change a frequency in accordance with a control voltage from the loop filter 34 to oscillate and output a desired frequency
Implementation Method 2
a phase comparator 32 configured to compare an external reference signal (Fref) with a 1/N divided signal to output a phase difference signal
Implementation Method 3
a loop filter 34 configured to smooth out an output voltage from the charge pump 33
Implementation Method 4
a frequency divider (divider) 36 configured to divide the output (internal reference signal) of the VCXO 35 to 1/N
Data Source
AI summary
Provided is an oscillation frequency control circuit for correcting its frequency, keeping the oscillation frequency stable when self-oscillating, and oscillating with a control voltage generated by making a fixed voltage given from outside variable. In the oscillation frequency control circuit, a CPU selects/outputs the control voltage preferentially according to a command of a control voltage selection. If the command is not given and the level of an outside reference signal detected by a detecting circuit is within an adequate range, it turns a select switch on. If the command is not given and the level of the outside reference signal is out of the adequate range, it turns the select switch off and outputs information about pulse generation stored in a memory to a PWM circuit.