LC-VCO Circuit with Varistor Capacitance for Wide Frequency Range
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Solution Overview
Problem
Conventional LC-VCOs have a limited frequency range due to the varactor's limited controllable capacitance, which also leads to increased area and power consumption, and replacing the varactor with a transformer results in high area consumption.
Innovation Solution
Replace the varactor with a varistor capacitance circuit using a voltage-controlled transistor-based variable resistor in series with a capacitor, and implement a negative feedback continuous time loop to map the phase locked loop control voltage to the varistor capacitance, allowing for a higher ratio of controllable capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a varactor is used in the LC-VCO, then the phase noise is good, but the frequency range is limited
Solution Approach 1:
The patent changes the fundamental parameter of capacitance control by replacing the varactor's voltage-to-capacitance relationship with a varistor's voltage-to-resistance relationship. This allows the equivalent capacitance to be controlled over a wider range by controlling the resistance through voltage, thereby expanding the frequency range while maintaining phase noise performance.
Solution Approach 2:
The patent introduces a varistor as an intermediary element between the control voltage and the capacitor. The varistor controls the equivalent capacitance by controlling its resistance, which in turn controls the charging/discharging rate of the capacitor. This intermediary approach enables wider frequency tuning range while maintaining good phase noise characteristics.
2Adaptability or versatility
If multiple VCOs are used to increase frequency range, then the frequency range increases, but the area and power consumption increase
Solution Approach 1:
The patent makes a single VCO circuit universal across a wide frequency range by using the varistor-capacitor combination. Instead of requiring multiple separate VCO circuits for different frequency ranges, this design enables one circuit to cover all frequency ranges, thereby reducing the total area and power consumption while maintaining wide frequency coverage.
3Adaptability or versatility
If a transformer is used to replace the varactor, then the frequency range increases, but the area consumption increases
Solution Approach 1:
The patent extracts the resistance control function from the transformer design and implements it separately using a varistor. This allows the main LC tank circuit to remain compact while the frequency tuning function is achieved through the varistor's resistance control, thereby reducing the overall area consumption compared to using a transformer for frequency tuning.
4Device complexity
If a varactor with fixed total capacitance is used, then the circuit is simple, but less than 50% of the total capacitance is controllable
Solution Approach 1:
The patent introduces dynamics into the capacitance control system by using a varistor whose resistance changes with applied voltage. This dynamic resistance control enables the equivalent capacitance to be continuously adjusted over a wide range, achieving more than 50% controllable capacitance ratio while maintaining circuit simplicity through the single varistor-capacitor combination.
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 solution achieves a 20% higher frequency range with reduced area and power consumption, supporting high-speed serializer/deserializer applications and improved jitter performance.
Implementation Method 1
The varistor capacitance circuit comprises a voltage-controlled transistor based variable resistor in series with a capacitor
Implementation Method 2
The LC tank circuit comprises a center tapped inductor connected in parallel to a varactor-less capacitor bank. The LC tank circuit resonates to produce an oscillating voltage at a frequency.
Implementation Method 3
The control circuit comprises an error amplifier and a conversion circuit configured to generate an output control voltage based on an input PLL control voltage
Data Source
AI summary
Embodiments herein disclose an inductor-capacitor voltage-controlled oscillator VCO circuit. The LC-VCO circuit includes a center tapped inductor connected in parallel with a varactorless capacitor bank, where the LC tank circuit resonates to produce an oscillating voltage; and a control circuit connected to a varistor capacitance circuit that comprises a voltage-controlled transistor based variable resistor in series with at least one capacitor, the varistor capacitance circuit being connected in parallel with the LC tank circuit and to a negative trans-conductance circuit. The control circuit includes an error amplifier and a conversion circuit configured to generate an output control voltage based on an input phase locked loop (PLL) control voltage, the output control voltage controlling a value of a capacitance for the varistor capacitance circuit through the variable resistor.