Delta-Sigma Modulator Fan Driver Circuit Design
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Solution Overview
Problem
Existing fan drive systems lack flexibility and accuracy in controlling fan rotational speed, particularly in systems requiring digital control for both pulse and linear voltage configurations, and face challenges in achieving compactness and high accuracy while maintaining power efficiency.
Innovation Solution
A driver circuit utilizing a delta-sigma modulator and oversampling techniques to generate either pulses or linear voltage based on digital control signals, implemented using digital design techniques to achieve compactness and high accuracy, with the option to include a low-pass filter for noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM signal generation is used to control fan speed, then digital control capability is achieved, but the circuit complexity increases and die size increases
Solution Approach 1:
The patent replaces complex analog PWM circuitry with a digital delta-sigma modulator that uses simple digital logic and a charge pump. The control is achieved through digital input values that directly control the charge pump operation, eliminating the need for complex analog signal generation circuits while maintaining full digital control capability.
Solution Approach 2:
The patent changes the control parameter from complex PWM duty cycle generation to simple digital input values controlling charge transfer. The fan speed is controlled by varying the digital input value to the delta-sigma modulator, which adjusts the charge pump operation, simplifying the control mechanism while maintaining precision.
2Power
If analog circuits are used to provide power signals to the fan, then power delivery capability is achieved, but die size increases and testability decreases
Solution Approach 1:
The patent replaces analog power signal generation circuits with a digital delta-sigma modulator combined with a charge pump. The digital logic requires significantly less silicon area than analog circuits while delivering the same power control capability to the fan motor.
Solution Approach 2:
The charge pump circuit serves multiple functions: it acts as both the power delivery mechanism and the digital-to-analog converter. This multi-functionality eliminates the need for separate analog output stages, reducing overall die size while maintaining power delivery capability.
3Measurement precision
If high precision fan control is implemented, then rotational speed accuracy is improved, but circuit complexity and die size increase
Solution Approach 1:
The patent implements feedback through the delta-sigma modulator architecture, where the quantization error is fed back and shaped to higher frequencies. This feedback mechanism provides high precision control by continuously correcting the charge pump output based on the difference between desired and actual fan speed, achieving accuracy without complex circuitry.
Solution Approach 2:
The patent uses periodic sampling and quantization in the delta-sigma modulator to achieve high precision control. By sampling the control signal at high rates and using noise shaping, the system achieves fine resolution in fan speed control through simple periodic digital operations rather than complex continuous analog circuits.
4Adaptability or versatility
If PWM control method is used, then fan speed control flexibility is achieved, but quantization noise affects control accuracy
Solution Approach 1:
The delta-sigma modulator uses feedback to shape quantization noise to higher frequencies that are less perceptible to the fan motor. The feedback loop continuously adjusts the charge pump output to minimize the impact of quantization errors, maintaining control flexibility while reducing noise.
Solution Approach 2:
The charge pump acts as an intermediary between the digital control signal and the analog fan motor. It converts digital charge packets into smooth analog current delivery, filtering out quantization noise inherent in digital PWM while maintaining the flexibility of digital control. The capacitor in the charge pump smooths the pulsed current into a continuous analog signal.
Data Source
AI summary
A fan driver circuit for powering a fan with a linear voltage may be designed using digital design techniques, resulting in a testable, accurate circuit on a smaller die size. The fan driver circuit may be configured to receive a digital control signal, which may be a sequence of numeric values, e.g. multiple-bit binary numbers, each indicative of a desired present rotational speed of the fan. The fan driver circuit may be implemented using a digital modulator, e.g. a delta-sigma modulator, with a simple low-pass filter, e.g. an RC-filter at the output, and may use oversampling based on a system clock, to shift in-band noise to out-of-band frequencies, and digital interpolation to filter out unwanted images from the upsampled digital control signal. The delta-sigma modulator may be constructed as a first-order delta-sigma modulator using an error-feedback structure to reduce die size.