Ring Oscillator Delay Cell with Kvco Equalization Across Frequency Bands
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Solution Overview
Problem
Conventional voltage-controlled oscillators (VCOs) in phase-locked loops (PLLs) using ring oscillators suffer from high phase noise and fluctuating voltage-controlled frequency (Kvco) values, complicating circuit design and increasing noise in the loop filter.
Innovation Solution
A delay cell comprising a differential amplifier, a switched capacitance bank, and a Kvco equalizer is introduced, allowing for adjustable capacitance and current compensation to maintain a constant Kvco value across different frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a ring oscillator is used to implement a VCO in a PLL, then the layout area is reduced and tuning range is widened, but phase noise increases and Kvco fluctuates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the bias current of the differential amplifier through a control signal. This allows the amplifier to operate in different regions (linear vs. saturation) to optimize performance across different frequency ranges, thereby maintaining constant Kvco and reducing phase noise while preserving the compact area advantages of ring oscillators
Solution Approach 2:
The patent implements feedback by detecting the actual oscillation frequency and generating a control signal that adjusts the bias current accordingly. This closed-loop feedback mechanism compensates for Kvco fluctuations and phase noise, ensuring stable operation across the tuning range while maintaining the area efficiency of the ring oscillator structure
2Device complexity
If conventional delay cells are used in the VCO, then the circuit is simple, but Kvco fluctuates according to changes in controlling voltage
Solution Approach 1:
The patent applies dynamics by making the bias current of the differential amplifier variable rather than fixed. The amplifier transitions between different operating states based on the control voltage, allowing the circuit to adapt its characteristics dynamically. This dynamic operation enables constant Kvco across the tuning range while maintaining reasonable circuit complexity
Solution Approach 2:
The patent changes the operating parameters of the differential amplifier by adjusting its bias current based on the control voltage. This parameter modulation compensates for the natural Kvco fluctuations in conventional delay cells, achieving stable frequency control without significantly increasing circuit complexity
3Adaptability or versatility
If Kvco fluctuates according to changes in controlling voltage, then the VCO can operate over a wide range, but the loop filter noise increases and design becomes complicated
Solution Approach 1:
The patent uses feedback to detect frequency deviations and generate corrective control signals that adjust the amplifier bias current. This feedback mechanism maintains constant Kvco across the tuning range, thereby simplifying the loop filter design and reducing noise while preserving wide frequency adaptability
Solution Approach 2:
The patent dynamically changes the bias current parameter of the differential amplifier to compensate for Kvco variations across the frequency tuning range. This parameter adjustment ensures that the VCO maintains consistent characteristics throughout its operating range, simplifying downstream circuit design including the loop filter
Data Source
AI summary
A delay cell for use in a ring oscillator and associated method is provided. The delay cell includes a differential amplifier, a switched capacitance bank, and a Kvco equalizer. The differential amplifier comprises a differential pair, a first load and a second load. The differential pair includes a positive input terminal, a negative input terminal, a positive output terminal, and a negative output terminal. The first load is coupled to the positive output terminal, and the second load is coupled to the negative output terminal. The switched capacitance bank has a plurality of controlled capacitor paths selectively connecting to the positive output terminal or the negative output terminal according to a capacitance controlling signal. The Kvco equalizer has an adjustable current source for providing a current to the Kvco equalizer according to a current controlling signal to compensate currents flowing through the first load and the second load.