Digital PLL Oscillator Control Using Delta-Sigma Noise Shaping
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Solution Overview
Problem
Conventional digitally controlled oscillators face accuracy issues due to power supply voltage fluctuations and process variability, leading to reduced analog output resolution and dynamic range, which affects the precision of high-frequency clock signal generation in digital PLLs.
Innovation Solution
A digitally controlled oscillator is designed with a high-order ΔΣ modulator and a first-order ΔΣ modulator, along with a low pass filter, to generate a pseudorandom digital output signal that is converted into an analog control signal, reducing quantization noise and improving signal-to-noise ratio, thereby enhancing the resolution and accuracy of frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional DA converter is used to generate analog control signal, then the circuit implementation is simple, but the accuracy of analog output voltage deteriorates due to power supply voltage fluctuation and the dynamic range is narrowed
Solution Approach 1:
The patent replaces the conventional DA converter (analog circuit) with a digital signal processing chain consisting of high-order ΔΣ modulator, first-order ΔΣ modulator, and low pass filter. This substitution of analog circuitry with digital processing eliminates the direct dependency on power supply voltage for analog output accuracy, as the digital domain is inherently more resistant to power supply fluctuations.
2Use of energy by moving object
If power supply voltage is reduced, then power consumption decreases, but the dynamic range of analog output voltage is narrowed leading to low resolution
Solution Approach 1:
The patent replaces the power-sensitive analog DA converter with a digital signal processing system. The digital domain operations (ΔΣ modulation, pulse width modulation, digital filtering) are inherently more power-efficient and less sensitive to supply voltage variations, allowing the system to maintain high resolution output even with reduced power supply voltage.
Solution Approach 2:
The patent introduces dynamic elements including high-order ΔΣ modulator for noise shaping, first-order ΔΣ modulator for pulse width modulation, and a low pass filter with selectable time constants. These dynamic components enable the system to adapt its response characteristics and maintain performance across varying power supply conditions.
3Measurement precision
If high-order ΔΣ modulator and first-order ΔΣ modulator are used, then quantization noise is reduced and signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The patent divides the signal processing function into two separate modulator stages: a high-order ΔΣ modulator for noise shaping and a first-order ΔΣ modulator for pulse width modulation. This segmentation allows each stage to be optimized for its specific function, achieving high signal-to-noise ratio while keeping individual stage complexities manageable.
Solution Approach 2:
The patent introduces a low pass filter as an intermediary component between the modulators and the oscillator control input. This filter mediates the transition from digital pulse signals to analog control voltage, smoothing the quantized output while preserving the noise-shaping benefits of the ΔΣ modulators.
Data Source
AI summary
A digitally controlled oscillator has a high-order ΔΣ modulator configured to be of at least an order higher than a first order and configured to input a digital control signal and output a pseudorandom digital output signal, a first-order ΔΣ modulator configured to input the pseudorandom digital output signal and generate a control pulse signal including a pulse width corresponding to the pseudorandom digital output signal, a low pass filter configured to pass a low frequency component of the control pulse signal, and an oscillator configured to generate a high-frequency output signal whose frequency is controlled based on the control pulse signal outputted by the low pass filter so as to be a frequency corresponding to the digital control signal.