Frequency Converter Current Matching for Voltage and Temperature Drift
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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 increased jitter 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 an analog output signal, decoupling frequency conversion from temperature and supply voltage variations, and using a charge/discharge circuit and reference circuit to maintain equal current magnitudes, thereby compensating for changes without additional compensation circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sample and hold mechanism with capacitor charging is used for frequency to voltage conversion, then the converter structure is simple, but the accuracy decreases and jitter increases due to temperature and supply voltage variations
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary between the frequency input and voltage output. The current mirror (comprising transistors Q1-Q4 and resistors R1-R2) acts as a mediating structure that converts frequency variations to current variations, which are then transformed to voltage variations through resistive elements. This intermediary mechanism isolates the conversion process from direct temperature and supply voltage effects, maintaining accuracy without significantly increasing overall system complexity.
2Ease of operation
If current-based frequency conversion is used, then the conversion process is straightforward, but the output becomes highly sensitive to temperature and supply voltage changes
Solution Approach 1:
The patent implements a feedback mechanism through the current mirror configuration. The current mirror automatically adjusts the output current to maintain a precise relationship with the input frequency, compensating for temperature and supply voltage variations. The resistive network (R1-R2) provides additional feedback that stabilizes the voltage output, ensuring reliability while maintaining operational simplicity.
3Device complexity
If capacitor charging current is directly correlated with output voltage, then the conversion is linear and simple, but parasitic capacitance noise increases with output voltage
Solution Approach 1:
The patent extracts the parasitic capacitance effect from the main conversion path by using a current mirror configuration. The current mirror isolates the charging current from direct voltage correlation, allowing the output voltage to be derived through resistive elements rather than direct capacitor voltage. This extraction removes the source of parasitic noise while maintaining the linear conversion characteristic through the current-proportional resistive network.
Data Source
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.