Digital PLL FIR Filtering for Quantization Noise Aliasing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Prior art phase lock loop (PLL) circuits suffer from significant low-frequency quantization noise due to aliasing, which degrades their performance and requires reducing the gain of the voltage-controlled oscillator (VCO) to mitigate this issue, but this compromise affects the circuit's ability to maintain lock on the reference signal.
Innovation Solution
Incorporating a multi-tap finite impulse response (FIR) filter and an array of digital-to-analog converters (DACs) to reduce aliasing of quantization noise at low frequencies, with the FIR filter placing notches in the spectrum to attenuate noise that aliases down to DC, thereby minimizing DC quantization error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the gain of the voltage-controlled oscillator (VCO) is reduced to mitigate quantization noise, then low-frequency quantization noise is reduced, but the circuit's ability to maintain lock on the reference signal deteriorates
Solution Approach 1:
The patent extracts and removes the harmful quantization noise components from the feedback signal before it reaches the phase detector. By using a notch filter tuned to the quantization noise frequency, the harmful noise is separated and eliminated from the feedback path, allowing the VCO gain to be increased without reintroducing the noise problem.
Solution Approach 2:
The notch filter acts as an intermediary element in the feedback path. It selectively attenuates quantization noise frequencies while allowing the useful feedback signal to pass through, thereby mediating between the need for high VCO gain and the need to suppress quantization noise.
2Reliability
If a high gain VCO is used to improve lock maintenance capability, then the ability to maintain lock on the reference signal is improved, but low-frequency quantization noise increases
Solution Approach 1:
The harmful quantization noise is extracted and removed from the feedback signal using a notch filter, enabling the use of high VCO gain without the penalty of increased noise. The filter selectively removes noise components at specific frequencies while preserving the useful signal.
Solution Approach 2:
The notch filter serves as an intermediary that allows high VCO gain operation by blocking the transmission of quantization noise from the VCO output back to the phase detector, thus mediating between high gain operation and noise suppression.
3Measurement precision
If additional power is consumed to correct output signals affected by quantization noise, then output signal accuracy is improved, but power efficiency deteriorates
Solution Approach 1:
The patent converts the harmful quantization noise into a manageable problem by filtering it in the frequency domain. Instead of attempting to correct noise effects through additional power-consuming operations, the notch filter proactively removes noise components, turning a potentially harmful signal into a controlled parameter.
Solution Approach 2:
The notch filter performs preliminary noise removal in the feedback path before the quantization noise can corrupt the output signal. This preventive approach eliminates the need for subsequent power-consuming correction operations, as the noise is removed upstream in the signal chain.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A digital phase lock loop circuit includes a phase detector, loop filter, finite impulse response filter (FIR), a plurality of digital to analog converters (DACs), a voltage controlled oscillator (VCO), and a divider. The FIR filter includes a predetermined number of taps, where each tap is connected to an input of one DAC in the plurality of DACs. The FIR filter attenuates high-frequency quantization error in a digital control signal that the plurality of DACs converts to an analog control signal for the VCO. The FIR filtered control signal reduces or eliminates quantization noise higher-frequency components that would otherwise be generated as DC quantization noise in a feedback signal generated by the divider.