Locked Loop Circuit Using an Untrimmed RC Oscillator Reference
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Solution Overview
Problem
Existing locked loop circuits face challenges with process variations in RC oscillators, leading to inaccurate reference frequency generation, which requires large and power-consuming digital-to-analog converters for calibration, resulting in increased area and power consumption.
Innovation Solution
A locked loop circuit that uses a frequency counter to measure the reference signal and adjust a multiplier to achieve the desired output frequency, eliminating the need for a digital-to-analog converter and allowing the RC oscillator to operate un-trimmed, reducing area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an RC oscillator is used to generate the reference frequency, then the area and cost are reduced compared to a crystal oscillator, but the frequency accuracy deteriorates due to process variations in resistors and capacitors
Solution Approach 1:
The patent implements a feedback mechanism where the actual output frequency of the RC oscillator is measured and fed back to a control circuit. The control circuit adjusts the oscillator components dynamically to compensate for process variations, thereby maintaining accurate reference frequency generation without requiring a large calibration DAC.
Solution Approach 2:
The patent replaces the conventional mechanical/calibration-based frequency adjustment mechanism with a digital control system. Instead of using a large DAC to physically adjust oscillator components, the system uses digital measurement and control logic to achieve frequency accuracy, reducing the area and power consumption associated with large calibration DACs.
2Measurement precision
If a feedback loop with calibration circuit is used to adjust the RC oscillator frequency, then the frequency accuracy is improved, but the device complexity and power consumption increase
Solution Approach 1:
The patent replaces complex analog calibration circuits with a digital measurement and control system. A frequency counter measures the oscillator output, and a control circuit processes this digital information to adjust the oscillator, simplifying the overall calibration architecture while maintaining accuracy.
Solution Approach 2:
The system implements self-adjusting capability where the oscillator automatically compensates for its own frequency deviations. The measurement and control circuitry continuously monitors and corrects the oscillator output without requiring external calibration equipment or complex manual adjustment mechanisms.
3Measurement precision
If a large DAC is used to generate control signals for the RC oscillator, then the frequency accuracy is improved, but the area and power consumption increase
Solution Approach 1:
The patent replaces the large analog DAC with a digital control system that uses frequency measurement and digital signal processing to achieve the same frequency adjustment function. This substitution eliminates the need for high-resolution DACs, significantly reducing area and power consumption while maintaining frequency accuracy.
Solution Approach 2:
The system uses digital measurement and control signals as a functional copy of what a large DAC would provide. Instead of using a physical DAC to generate analog control voltages, the patent uses digital frequency information to control the oscillator directly, achieving the same effect with much smaller circuitry.
Data Source
AI summary
A circuit includes a frequency detector generating a comparison signal as a function of a comparison between a reference signal and a feedback signal. An oscillator generates an output signal as a function of the comparison signal. A frequency divider, in operation, divides the output signal by a division value to produce the feedback signal as having a frequency that is a multiple of a frequency of the reference signal. A frequency counter circuit measures the frequency of the reference signal and generates a count signal based thereupon. A control circuit adjusts the division value used by the frequency divider, in operation, based upon the count signal.