Frequency Converter Circuit With Matched Current Source Compensation
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Solution Overview
Problem
Existing frequency to voltage converters, particularly those based on sample and hold mechanisms, suffer from decreased accuracy and noise issues due to temperature and supply voltage variations, making them unsuitable for high accuracy clock designs.
Innovation Solution
A frequency to voltage converter system utilizing two synchronously operating current sources to generate equal electrical currents, which are used in a charge/discharge circuit and a reference circuit to produce an analog output signal independent of temperature and supply voltage variations, eliminating the need for compensation circuits and minimizing noise sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sample and hold mechanisms are used for frequency to voltage conversion, then the converter structure is simple, but the measurement precision deteriorates due to temperature and supply voltage variations
Solution Approach 1:
The patent introduces a reference current source as an intermediary element that mirrors the characteristics of the charging current source. This reference current source generates a reference voltage that automatically tracks and compensates for temperature and supply voltage variations, thereby maintaining measurement precision without complicating the overall converter structure.
Solution Approach 2:
The patent utilizes the parameter changes in current sources due to temperature and supply voltage variations by creating a matched reference current source. Both the charging current source and reference current source experience identical parameter changes, allowing the differential measurement to cancel out these variations and maintain accuracy.
2Ease of operation
If charging current is used to generate output voltage, then the conversion process is straightforward, but the measurement precision deteriorates due to current dependencies
Solution Approach 1:
The patent uses a reference voltage generated from a reference current source as an intermediary for comparison. Instead of directly using the charging current to generate the output voltage, the system compares the capacitor voltage (charged by the current) against the reference voltage, eliminating direct current dependency in the output generation process.
Solution Approach 2:
The patent replaces the direct current-to-voltage conversion mechanism with a voltage comparison mechanism. By using a comparator to compare voltages rather than directly converting current to voltage, the system eliminates the harmful effects of current variations while maintaining the simplicity of the conversion process.
3Measurement precision
If voltage compensation circuits are added to improve accuracy, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent implements self-service compensation by using a reference current source that automatically tracks and compensates for environmental variations. The system compensates for its own errors through the inherent matching of the reference current source to the charging current source, eliminating the need for external voltage compensation circuits and reducing device complexity.
4Measurement precision
If temperature compensation circuits are added to reduce jitter, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent achieves self-service temperature compensation through the matched reference current source that experiences identical temperature effects as the charging current source. The automatic tracking and cancellation of temperature-induced variations occur without requiring separate temperature compensation circuits, thereby maintaining measurement precision while avoiding increased device complexity.
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 system achieves high accuracy and reduced jitter by maintaining equal current magnitudes despite temperature and supply voltage fluctuations, ensuring precise frequency-to-voltage conversion without dependency on current or temperature compensation.
Implementation Method 1
The first and second current sources substantially synchronously supply respective electrical currents of substantially equal magnitude to the charge/discharge circuit and the reference circuit. During operation, the electrical currents remain substantially equal in magnitude due to temperature variations and supply voltage variations having a substantially equal effect on the respective first and second current sources.
Implementation Method 2
The charge/discharge circuit uses the first electrical current to selectively charge and discharge a capacitor included in the charge/discharge circuit based on the frequency of the electrical input signal.
Implementation Method 3
The reference circuit generates a reference voltage using the second electrical current applied to a resistor.
Implementation Method 4
A comparator circuit included in the converter circuit generates an analog output signal indicative of the frequency of the input signal based on comparison of the reference voltage to a voltage of the capacitor.
Data Source
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AI summary
A voltage to frequency conversion system may be used in association with clock related applications such as a closed loop oscillator. The voltage to frequency conversion system includes independent current sources that are synchronously operated to generate substantially the same respective output currents under varying temperature and supply voltage conditions. One of the current sources is used to generate a reference voltage, and the other of the current sources is used to charge a capacitor in a predetermined ramp. The capacitor may be selectively charged and discharged based on a frequency of an input signal, and an average of the variable charge voltage of the capacitor may be compared to the reference voltage to generate an analog output signal indicative of frequency.