Voltage-Controlled Oscillator Current Mirror for Low-Voltage Stability
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Solution Overview
Problem
Existing voltage-current conversion circuits in voltage-controlled oscillators face challenges in maintaining stable frequency output at low supply power and temperature changes, particularly due to changes in threshold voltage of input transistors and saturation issues in current sources.
Innovation Solution
A voltage-controlled oscillator design incorporating a voltage-current conversion circuit with a replica circuit and current mirror configuration, using NMOS transistors with the same temperature characteristics to generate a control current based on the difference between first and second currents, ensuring stable frequency output across temperature variations and low supply power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a voltage-current conversion circuit is configured as a differential structure, then it can convert control voltage to control current, but it requires an operating voltage in a region where the current source is saturated, making it difficult to operate at low supply power
Solution Approach 1:
The voltage-current conversion circuit is divided into two separate single-structure circuits instead of one differential structure. Each circuit independently converts voltage to current, eliminating the need for high operating voltage required by saturated current sources in differential configurations, thereby enabling low supply power operation.
Solution Approach 2:
Instead of using a differential structure that requires current sources in saturation (high voltage operation), the invention inverts the approach by using single-structure circuits that operate in the triode region, allowing voltage-controlled current generation at low supply voltages.
2Device complexity
If the voltage-current conversion circuit is composed of a single structure, then it simplifies the circuit design, but the threshold voltage of the input transistor changes with temperature, causing the compliance range to change
Solution Approach 1:
The invention uses two identical single-structure voltage-current conversion circuits with matching transistors. By copying the circuit structure and ensuring component matching, temperature-induced threshold voltage changes affect both circuits equally, allowing the differential output to cancel out temperature variations and maintain stable compliance range.
Solution Approach 2:
The invention compensates for temperature-induced threshold voltage changes by using matched transistor pairs in identical circuit configurations. The differential structure converts common-mode temperature variations into common-mode signals that are rejected at the output, maintaining stable electrical characteristics across temperature ranges.
3Ease of operation
If a differential structure is used for voltage-current conversion, then it can provide balanced output, but it increases the circuit complexity and makes it difficult to achieve low supply power operation
Solution Approach 1:
The differential function is segmented into two independent single-structure circuits rather than implemented as one complex differential block. Each circuit independently generates a current proportional to its input voltage, achieving balanced differential output through the combination of two simple, identical circuits rather than one complex circuit.
Data Source
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AI summary
The voltage-controlled oscillator can include a voltage-current conversion circuit that outputs a control current corresponding to the control voltage, and a ring oscillator that generates an output signal with a frequency corresponding to the control current. According to an embodiment, by using a voltage-current conversion circuit, it is possible to design a voltage-controlled oscillator that can operate even with a relatively low supply power and have stable characteristics even when the temperature changes.