CCO PLL Loop Filter Without Zero Resistor for Lower Phase Noise
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Solution Overview
Problem
Existing loop filters for current-controlled oscillator-based phase-locked loops face challenges in achieving small implementation area and low noise contribution, with high values of resistance and capacitance leading to increased phase noise and larger implementation areas.
Innovation Solution
A loop-filter design incorporating a capacitor, a voltage-to-current converter, and a charge pump, where the charge pump generates an additional current component to eliminate the need for a zero-determining resistor, allowing for a smaller capacitance value and reduced implementation area, while maintaining stability and low noise through an active cascode configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If high values of resistance and capacitance are used in the loop filter, then the implementation area is reduced, but the phase noise increases
Solution Approach 1:
The patent changes the fundamental parameters of the loop filter by replacing the traditional RC filter with an active filter using a voltage-to-current converter and charge pump. This allows the use of smaller capacitance values while maintaining filter performance and reducing phase noise, as the active circuitry provides the necessary filtering function without relying on large passive components.
Solution Approach 2:
The patent substitutes the passive mechanical RC filtering mechanism with an active electronic filtering mechanism. The voltage-to-current converter and charge pump create an active filter that achieves the same low-pass filtering effect without requiring large resistance and capacitance values, thereby reducing implementation area while maintaining or improving noise performance.
2Area of stationary object
If the capacitance value is reduced to decrease implementation area, then the implementation area is reduced, but the stability and noise performance deteriorate
Solution Approach 1:
The patent replaces the passive RC filtering system with an active filtering system using a voltage-to-current converter and charge pump. This substitution enables the use of smaller capacitance values while maintaining stability through the active circuitry's inherent properties, such as the charge pump's ability to maintain consistent current output and the voltage-to-current converter's stable transconductance.
Solution Approach 2:
The voltage-to-current converter acts as an intermediary element that transforms the voltage output of the loop filter into a current signal that drives the charge pump. This intermediary conversion enables the system to achieve stable operation with smaller capacitance values by decoupling the filtering function from the capacitance magnitude and instead relying on the active circuit's controlled current delivery.
3Stability of the object's composition
If a zero-determining resistor is used in the loop filter, then the bandwidth stability is improved, but the implementation area increases
Solution Approach 1:
The patent extracts and removes the zero-determining resistor from the traditional loop filter configuration. By eliminating this component, the implementation area is reduced. The bandwidth stability function is instead achieved through the active voltage-to-current converter and charge pump circuitry, which provide stable operation without requiring the additional resistive element.
Solution Approach 2:
The patent substitutes the passive resistive bandwidth control mechanism with an active electronic control mechanism. The voltage-to-current converter and charge pump replace the function of the zero-determining resistor in establishing bandwidth stability, allowing the system to achieve the same stability performance without the area overhead of the additional resistor component.
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 reduces phase noise and implementation area, achieving stable bandwidth and efficient frequency control with reduced transconductance, enabling smaller and lower noise phase-locked loops.
Implementation Method 1
The voltage-to-current converter (V-to-I) circuit is coupled to receive the voltage at the input node, and to generate a first component of an output current at an output node of the loop-filter
Implementation Method 2
The charge pump of the loop-filter generates a second component of the output current at the output node
Implementation Method 3
The capacitor is coupled between an input node of the loop-filter and a constant reference potential
Data Source
AI summary
A loop filter of a phase-locked loop (PLL) that uses a current-controlled oscillator (CCO) includes a capacitor, a voltage-to-current (V-to-I) converter, and a charge pump. The input node of the loop filter receives a first current from an external charge pump. The combination of the capacitor and the V-to-I converter generates a first component of the output current of the loop filter based on the first current. The charge pump of the loop filter generates a second component of the output current. The loop filter is implemented without the need for a zero-frequency-determining resistor, the resistor instead being realized by the product of the first current, the second component of the output current and the transconductance of the V-to-I converter. Phase noise reduction in the PLL, as well as implementation of the loop filter with a smaller area, are thus made possible.