PLL Loop Filter With Digital Capacitance Multiplication
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Solution Overview
Problem
Existing phase lock loop (PLL) circuits face challenges in achieving stability and precise capacitance multiplication without increasing bandwidth, particularly in low bandwidth applications, due to the difficulty in integrating large capacitors on integrated circuits and the inefficiencies of dual path charge pump systems which lead to increased power consumption and noise.
Innovation Solution
A digitally configured loop filter that uses a single charge pump and a blocking circuit to allow only a 1/N portion of phase error pulses to charge or discharge the integral capacitor, effectively multiplying the capacitance by a factor of N, thereby enhancing stability without the need for additional IC area or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large capacitor is used to increase stability, then the damping factor is improved, but the IC area required increases significantly
Solution Approach 1:
The patent changes the operational parameters of the charge pump by varying its current dynamically. By increasing the charge pump current during specific phases, the system achieves the effect of a larger capacitor without physically increasing the capacitor size, thus improving damping factor while maintaining small IC area
Solution Approach 2:
The patent implements periodic modulation of the charge pump current with a frequency N times the reference frequency. This periodic action creates the effect of capacitance multiplication by N, allowing the system to achieve high damping factor with a small physical capacitor, resolving the contradiction between stability and IC area
2Stability of the object's composition
If a dual path charge pump system is used to achieve capacitance multiplication, then the damping factor is improved, but the power consumption and device complexity increase
Solution Approach 1:
The patent makes a single charge pump perform multiple functions by dynamically varying its current. The same charge pump handles both the base charging current and the multiplied current effect through periodic modulation, eliminating the need for a second charge pump and reducing power consumption while achieving the desired damping factor
Solution Approach 2:
The patent merges the functions of two separate charge pumps into a single charge pump with variable current capability. By combining the integral and proportional paths into one unified charge pump structure with dynamically controllable current, the system achieves capacitance multiplication with reduced power consumption and simpler circuitry
3Stability of the object's composition
If a dual path charge pump system is used to achieve capacitance multiplication, then the damping factor is improved, but the circuit complexity and cost increase
Solution Approach 1:
The patent makes a single charge pump perform multiple functions by dynamically varying its current. The same charge pump handles both the base charging current and the multiplied current effect through periodic modulation, eliminating the need for a second charge pump and reducing power consumption while achieving the desired damping factor
Solution Approach 2:
The patent introduces dynamic control of the charge pump current through a current controller that responds to a modulation signal. This dynamic adjustment allows the charge pump to achieve capacitance multiplication effect without requiring additional static circuit components, thereby reducing overall circuit complexity
4Stability of the object's composition
If a dual path charge pump system is used to achieve capacitance multiplication, then the damping factor is improved, but the noise contribution to the PLL circuit increases
Solution Approach 1:
The patent extracts and eliminates the second charge pump from the dual path system, keeping only the essential single charge pump with variable current capability. By removing the redundant proportional charge pump path, the system reduces noise sources while maintaining the capacitance multiplication effect through current modulation
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
This solution allows for precise control of the capacitance multiplication factor, reducing IC area and power consumption while maintaining similar operating parameters to traditional PLLs, thus addressing the limitations of dual path charge pump systems.
Implementation Method 1
The integral capacitor C1 integrates the error current (integral path) to set an average oscillator frequency
Implementation Method 2
A blocking circuit is configured to allow a 1/N portion of the phase error pulses to charge or discharge the integral capacitor C1, where N is an integer. Because the blocking circuit is blocking a (N−1)/N portion of the phase error pulses, it takes the charge pump N times the time or N times longer when N is greater than 1 to charge or discharge the integral capacitor C1 to a certain amount of charge. Thus, the integral capacitor C1 having a capacitance C appears to have a capacitance of N×C.
Data Source
AI summary
Systems and methods for capacitance multiplication using one charge pump for a phase lock loop employ a digital controlled loop filter that operates in a time division mode. Embodiments of the loop filter block the current from the charge pump according to the digital control, such that the charge pump cannot charge or discharge the integral capacitor when the digital control is enabled. Because at least a portion of the current is blocked, it takes more time for the charge pump to charge or discharge the capacitor to a certain level. The capacitor then appears to be larger than its actual value with respect to operation of the phase lock loop.