Charge Pump Sensor Driver for High PSRR at Baseband
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Solution Overview
Problem
Traditional sensor drivers suffer from power supply rejection weaknesses at discrete frequencies due to intermixing of supply ripple with the drive frequency, leading to significant errors, such as 4000 times the noise floor or least significant bit (LSB).
Innovation Solution
A device comprising a charge pump and an error amplifier is used, where the charge pump decouples the input voltage from the output voltage during distinct phases, mixing frequency disturbances back to baseband, and the error amplifier removes these disturbances, thereby providing a high power supply rejection ratio. The charge pump includes flying capacitors and DC capacitors arranged in specific configurations to accommodate various voltage conversion ratios and supply ranges, ensuring improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sensor drivers are used, then the device complexity is low, but the power supply rejection ratio deteriorates at discrete frequencies due to intermixing of supply ripple with drive frequency
Solution Approach 1:
The sensor driver is segmented into multiple functional blocks: a charge pump circuit for voltage multiplication, a modulation circuit for frequency conversion, and a demodulation circuit for signal recovery. This segmentation allows each block to perform its specific function optimally, with the charge pump generating a high-frequency drive signal and the modulation/demodulation circuits handling the signal processing, thereby achieving high power supply rejection ratio while managing complexity through functional decomposition
Solution Approach 2:
A modulation circuit is introduced as an intermediary between the charge pump output and the sensor. This intermediary circuit converts the high-frequency charge pump output to a lower frequency suitable for driving the sensor, while also providing isolation from power supply ripple. The intermediary modulation circuit acts as a buffer that prevents direct coupling of power supply disturbances to the sensor, thereby improving power supply rejection ratio
2Measurement precision
If the charge pump operates at high frequency to improve signal-to-noise ratio, then the signal-to-noise ratio improves, but the intermixing of supply ripple with drive frequency increases causing errors
Solution Approach 1:
The charge pump operates in periodic cycles, alternating between a first phase where it generates a high-frequency drive signal and a second phase where it resets. This periodic operation allows the system to achieve high signal-to-noise ratio during the drive phase while the reset phase provides natural isolation from power supply ripple. The periodic nature of the charge pump operation, combined with synchronous demodulation, enables frequency separation that prevents intermixing of supply ripple with the drive signal
Solution Approach 2:
A feedback mechanism is implemented where the output of the sensor is fed back through a demodulation circuit that is synchronized with the charge pump operation. This feedback loop allows the system to recover the modulated signal while rejecting high-frequency noise and power supply ripple. The synchronous demodulation in the feedback path ensures that only the desired signal frequency is recovered, while frequency-disturbed signals are rejected, thereby improving measurement precision
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
The solution significantly reduces errors associated with power supply rejection, achieving a signal-to-noise ratio improvement and reducing noise metrics by orders of magnitude, from over 4000 pascal to less than 4 pascal, effectively addressing the limitations of traditional systems.
Implementation Method 1
The charge pump includes a first number of flying capacitors and a second number of Direct Current (DC) capacitors that are arranged in a defined configuration
Implementation Method 2
The charge pump includes circuitry that decouples the input voltage of the charge pump from the output voltage of the charge pump and in the process mixes defined frequency disturbances back to baseband
Implementation Method 3
The error amplifier is configured to drive a micro-electromechanical system (MEMs) capacitive sensor. The error amplifier receives the output voltage from the charge pump and removes defined mixed down frequency disturbances
Implementation Method 4
The first number of flying capacitors and the second number of DC capacitors are arranged in a parallel configuration connected to the input. Further, during a second phase of the distinct phases, the first number of flying capacitors are configured in a parallel arrangement and the second number of DC capacitors are connected in series with the parallel arrangement towards the output
Data Source
AI summary
A sensor driver providing high power supply rejection ratio is provided herein. A circuit can include a charge pump that comprises an input terminal and an output terminal, wherein the input terminal is operatively connected to a voltage supply. The charge pump further comprises circuitry that decouples an input voltage from the voltage supply from an output voltage of the charge pump and mixes defined frequency disturbances back to baseband. The circuit also includes an error amplifier configured to provide high power supply rejection ratio at baseband, wherein the output terminal of the charge pump is operatively connected to an input node of the error amplifier. Further, the circuit includes a capacitive micro-electromechanical system sensor operatively connected to an output node of the error amplifier.