Switched-Capacitor Reference Voltage Circuit for Audio-Band PSRR
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Solution Overview
Problem
Conventional reference voltage generating circuits for ADC and DAC require large capacitors and resistors, leading to high design complexity and cost, and fail to achieve sufficient power supply rejection ratio (PSRR) in audio-band applications.
Innovation Solution
A reference voltage generating circuit that quickly switches capacitors to filter out noise, using a configuration of four switches and two capacitors to sample and redistribute charges, eliminating the need for large resistors and achieving improved PSRR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If large capacitors and resistors are used to generate reference voltage for audio band, then the corner frequency can be lowered below 20 Hz, but the design complexity and cost increase significantly
Solution Approach 1:
The patent employs periodic switching of capacitors through multiple stages (first stage, second stage, third stage) controlled by clock signals. This periodic action allows the circuit to achieve low corner frequency performance without requiring physically large capacitors, as the switching mechanism effectively creates a time-averaged low-pass filter response.
Solution Approach 2:
The reference voltage generation is divided into multiple discrete stages with different capacitor configurations. Each stage uses specific capacitors (first capacitor, second capacitor, third capacitor) that are switched in and out of the circuit at different times. This segmentation allows the system to achieve the equivalent filtering effect of a large capacitor through coordinated switching of smaller capacitors.
2Reliability
If conventional RC filtering is used to generate reference voltage, then the circuit structure is simple, but the power supply rejection ratio (PSRR) cannot achieve -60 dB across the audio frequency band
Solution Approach 1:
The patent transitions from a static RC filter to a dynamic capacitor switching architecture. The capacitors are dynamically switched between different connections (to predetermined voltage, to reference level, between capacitors) based on clock signals. This dynamic operation enables the circuit to achieve superior PSRR performance across the audio band by actively managing charge distribution and voltage stabilization.
Solution Approach 2:
The circuit changes the effective capacitance values and connections dynamically through switching. Different capacitor combinations are activated at different stages, effectively changing the filtering parameters in real-time to optimize PSRR performance across different frequency ranges within the audio band.
3Measurement precision
If external voltage source VDD and ground voltage GND are used to generate reference voltages, then the reference voltage levels can be higher, but noise filtering becomes more challenging
Solution Approach 1:
The patent introduces multiple capacitors and switching mechanisms as intermediary elements between the external voltage source and the reference voltage output. These intermediaries (first capacitor, second capacitor, third capacitor, and associated switches) actively filter and condition the voltage, isolating the reference voltage from noise present in the external VDD supply while maintaining the desired voltage level.
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 allows for cost-effective generation of low-noise, low-frequency reference voltages with improved PSRR, suitable for audio-band applications without the need for large resistors, enhancing the performance of ADC and DAC circuits.
Implementation Method 1
a first capacitor, comprising a first end and a second end; a second capacitor, comprising a third end and a fourth end
Implementation Method 2
a first switch, for alternatively coupling the predetermined voltage to the second end of the first capacitor; a second switch, for alternatively coupling the third end of the second capacitor to the first end of the first capacitor
Data Source
AI summary
A reference voltage generating circuit includes a first capacitor having a first end and a second end; a second capacitor having a third end and a fourth end; a first switch for selectively coupling a predetermined voltage to the first end of the first capacitor; a second switch for selectively coupling the third end of the second capacitor to the first end of the first capacitor; a third switch for selectively coupling the first end of the first capacitor to a reference voltage level; and a fourth switch for selectively coupling the second end of the first capacitor to a reference voltage level; wherein the first capacitor samples the predetermined voltage in a first stage and re-distributes charges to the second capacitor in a second stage.