Supply-Regulated VCO with Auxiliary Current for Noise Rejection
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Solution Overview
Problem
Phase-Locked Loops (PLLs) with supply-regulated Voltage-Controlled Oscillators (VCOs) face challenges in rejecting supply noise, particularly due to limited bandwidth in the supply regulation control loop, leading to 'peaking' in supply noise sensitivity and increased phase noise from replica transistors, which affects oscillator stability and frequency control.
Innovation Solution
The introduction of an auxiliary supply current circuit that reduces the load on the main supply regulation control loop, allowing for a smaller transistor size and increased bypass capacitor capacitance, thereby reducing parasitic capacitances and enhancing noise rejection without destabilizing the loop. This is achieved through a replica load and an auxiliary supply regulation control loop, or a digitally-controlled current source maintaining a constant ratio of auxiliary to main supply current over the VCO's frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the supply regulation control loop bandwidth is increased to improve noise rejection, then supply noise rejection is improved, but loop stability is compromised due to peaking in the supply noise sensitivity transfer function
Solution Approach 1:
The supply current to the oscillator is segmented into two independent paths: a main supply current path with a first bypass capacitor for noise rejection, and an auxiliary supply current path with a second bypass capacitor. This segmentation allows each path to be optimized independently, with the auxiliary path providing additional noise filtering without destabilizing the main regulation loop.
Solution Approach 2:
An auxiliary supply current circuit is introduced as an intermediary element that provides additional supply current to the oscillator. This auxiliary circuit includes its own bypass capacitor and regulation mechanism, acting as a mediator that enhances noise rejection while isolating the main supply regulation loop from instability issues.
2Object-affected harmful factors
If the bypass capacitor capacitance is increased to improve high-frequency noise rejection, then high-frequency noise rejection is improved, but the dominant pole frequency decreases causing loop instability
Solution Approach 1:
The bypass capacitance is segmented into two separate capacitors: a first bypass capacitor in the main supply path and a second bypass capacitor in the auxiliary supply path. This allows the total effective bypass capacitance to be increased for better high-frequency noise rejection while each individual capacitor maintains the dominant pole frequency within stable ranges.
3Speed
If transistor size is reduced to decrease parasitic capacitances and increase dominant pole frequency, then dominant pole frequency is increased, but the supply regulation control loop cannot provide sufficient supply current
Solution Approach 1:
The supply current provision is segmented between a main supply current source with a smaller transistor (providing higher dominant pole frequency) and an auxiliary supply current source with its own transistor (providing additional current). This segmentation allows the main regulation loop transistor to be smaller for better speed response while the auxiliary source compensates for the reduced current capability.
Solution Approach 2:
An auxiliary supply current circuit acts as an intermediary that supplements the main supply current. This auxiliary circuit includes a dedicated transistor and bypass capacitor, providing additional current capability without requiring the main regulation transistor to be oversized, thus preserving the dominant pole frequency.
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 reduces supply noise sensitivity peaking, minimizes low-frequency noise impact, and stabilizes the PLL loop, improving overall noise rejection and frequency control accuracy by increasing the dominant pole frequency and bypass capacitor effectiveness without compromising loop stability.
Implementation Method 1
bypass capacitor 6 is provided to shunt such high frequency noise to ground so that oscillator 7 is not unduly affected by such noise
Implementation Method 2
The supply regulation control loop circuit 5 operates to keep signal ICTRL 17 a function of control signal VCTRL 15
Data Source
AI summary
A supply-regulated VCO exhibits reduced or no supply sensitivity peaking. The VCO includes an oscillator whose supply current is regulated to control the oscillating frequency of the oscillator. A VCO input signal controls the supply current so that there is a relationship between the input signal and the oscillator output frequency. Power supply noise that might otherwise affect oscillator operation is shunted from a supply current input lead of the oscillator to ground by a bypass capacitor. In one example, an auxiliary circuit supplies an auxiliary supply current to the oscillator, thereby reducing the amount of supply current a supply regulation control loop circuit must supply. In another example, a supply regulation control loop circuit supplies a control current to a main oscillator, but the bypass capacitor is not coupled to this oscillator but rather is coupled to a slave oscillator that is injection locked to the main oscillator.