Programmable Ramp Signal Circuit for Accurate ADC Linearity
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Solution Overview
Problem
Existing ramp generating circuits for analog-to-digital converters (ADCs) are either complex or introduce inaccuracies in real-world applications.
Innovation Solution
A ramp generating circuit that includes a constant reference voltage generator, a programmable current generator (either sink or source), and an output buffer, which controls the slope of the voltage ramp signal by adjusting the programmable current settings, ensuring linearity and flexibility for different operational modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing ramp generating circuits are used, then ADC functionality is provided, but the circuits are either very complex or create inaccuracies
Solution Approach 1:
The circuit is divided into distinct functional modules: a reference voltage generator that provides a stable baseline, a programmable current source that generates the ramp signal, and a capacitor that integrates the current to produce the voltage ramp. This segmentation allows each module to be optimized independently for accuracy while maintaining overall circuit simplicity.
Solution Approach 2:
The programmable current source can be configured to generate different ramp slopes and directions (rising or falling) by changing control parameters, making it universally applicable to various ADC requirements without requiring separate dedicated circuits for each function.
2Adaptability or versatility
If programmable current settings are used to control ramp slope, then adaptability for different operational modes is improved, but circuit complexity increases
Solution Approach 1:
The circuit achieves adaptability by changing the control parameters of the programmable current source (such as control voltage levels or digital control words) rather than changing the physical circuit structure. This allows the same hardware to generate different ramp characteristics for different ADC operational modes.
Solution Approach 2:
The programmable current generator includes built-in control logic that automatically adjusts the ramp parameters based on input control signals, eliminating the need for external complex control circuitry and reducing overall system complexity while maintaining versatility.
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 provides a simple and accurate method for generating voltage ramp signals, improving linearity and adaptability for various imaging device applications, such as CMOS imagers, by controlling the slope of the ramp signal through programmable current settings, thus enhancing the performance of ADCs.
Implementation Method 1
a reference capacitor (16) coupled to a voltage ramp signal node (19A)
Implementation Method 2
controlling charging or discharging of the reference capacitor (16) with a programmable current generator (15)
Data Source
AI summary
An apparatus and method for generating a ramp signal includes applying a constant reference voltage to a reference capacitor and controlling charging or discharging of the reference capacitor with a programmable current generator to provide the ramp signal at a ramp signal node. The method can include, buffering the ramp signal to an output node to drive a load. When generating the ramp signal having a negative slope, the programmable current generator includes a programmable current sink coupled to the ramp signal node. When generating the ramp signal having a positive slope, the programmable current generator includes a programmable current source that is coupled between a positive power supply node and the ramp signal node. When generating the ramp signal having a bidirectional slope, the programmable current generator includes a programmable current source and a programmable current sink.