Companding Current ADC for High Resolution at Microwatt Power
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Solution Overview
Problem
Existing analog to digital converters (ADCs) are highly consumptive of power and provide relatively low resolution, making them unsuitable for applications with limited power budgets and requiring high levels of performance.
Innovation Solution
A novel ADC design that enables high-resolution digital signal conversion with low power consumption by incorporating a single-line drive and sense capability, allowing simultaneous power provision and signal sensing, and utilizing a comparator and digital circuit to convert analog current signals into high-resolution digital format.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ADC designs are used, then power consumption is high, but resolution is limited
Solution Approach 1:
The ADC is segmented into multiple sub-ADCs, each handling a portion of the input range. This allows parallel processing of multiple bits simultaneously, achieving high resolution without requiring a single high-power converter. Each sub-ADC operates at lower power while the combined system delivers high-resolution output.
Solution Approach 2:
The system performs preliminary companding (compression/expansion) of the analog input signal before conversion. By pre-processing the signal to match the non-linear characteristics of the human perception or specific application requirements, the ADC can achieve higher effective resolution with reduced quantization noise, thereby improving measurement precision without increasing power consumption.
2Measurement precision
If high-resolution conversion is implemented, then power consumption increases, but this is unacceptable for low-power applications
Solution Approach 1:
The ADC employs dynamic element matching and time-interleaved conversion techniques where conversion elements are dynamically switched and activated based on the input signal characteristics. This allows the system to activate only the necessary number of conversion elements for the current signal level, achieving high resolution when needed while consuming minimal power during low-activity periods.
Solution Approach 2:
The conversion process uses periodic sampling and time-interleaved multiple sub-ADCs operating at different phases. By distributing the conversion workload across multiple periodic cycles and sub-converters, each sub-ADC can operate at lower resolution and power consumption, while the combined output achieves high overall resolution through temporal multiplexing.
3Measurement precision
If conventional ADC architectures are used, then power consumption is high, but resolution is relatively low
Solution Approach 1:
Multiple low-resolution sub-ADCs are merged into a single high-resolution conversion system. Each sub-ADC processes a portion of the signal with reduced power consumption, and their outputs are combined through digital signal processing to achieve the final high-resolution result. This merging approach distributes the power load while achieving superior resolution.
Solution Approach 2:
A companding function acts as an intermediary between the analog input and the digital conversion process. This non-linear transformation pre-distorts the signal to compensate for quantization effects, allowing the subsequent low-power ADC to achieve higher effective resolution. The companding function serves as a mediator that enhances the efficiency of the conversion process without requiring additional power.
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 ADC achieves significant power savings of up to 10× compared to prior art, supports a broad range of current sensing from pico-amps to milli-amps, and is suitable for low-power applications like bio-medical sensors, with bandwidths from DC to over 10 MHz.
Implementation Method 1
utilizing a comparator and digital circuit to convert analog current signals into high-resolution digital format
Data Source
AI summary
An analog to digital converter (ADC) senses an analog signal (e.g., a load current) to generate a digital signal. The ADC operates based on a load voltage produced based on charging of an element (e.g., a capacitor) by a load current and a digital to analog converter (DAC) output current (e.g., from a N-bit DAC). The ADC generates a digital output signal representative of a difference between the load voltage and a reference voltage. This digital output signal is used directly, or after digital signal processing, to operate an N-bit DAC to generate a DAC output current that tracks the load current. The digital output signal provided to the N-bit DAC is an inverse function of the load current. The ADC is operative to sense very low currents (e.g., currents as low as 1s of pico-amps) and consume very little power (e.g., less than 2 μW).