Differential CTIA Circuit for Current Signal Arithmetic
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Solution Overview
Problem
Existing systems face challenges in amplifying and digitizing the difference between small current signals from optical sensors without saturating the transimpedance amplifier, leading to limited digital resolution and increased power consumption in RF transmission and A-D conversion.
Innovation Solution
A circuit with a multiplexer and differential capacitive transimpedance amplifier that integrates currents with tunable capacitances and current mirrors, allowing for precise gain control and polarity-dependent integration to generate the signal difference, enabling single A-D conversion and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate A-D conversion of two current signals is performed, then the dynamic range is extended, but the power consumption increases and the communication frequency must be doubled
Solution Approach 1:
The patent combines two separate A-D conversion operations into a single A-D conversion by performing analog addition of the two current signals before conversion. The sum signal contains both magnitude and polarity information, allowing the ADC to capture the full dynamic range of both input signals while operating at a single communication frequency, thereby halving the power consumption compared to separate conversions.
Solution Approach 2:
The analog addition circuit serves multiple functions simultaneously: it sums the two current signals, preserves the dynamic range information through polarity encoding, and prepares a single signal suitable for A-D conversion. This multi-functional approach eliminates the need for separate conversion paths while maintaining measurement precision.
2Measurement precision
If the TIA gain is increased to amplify small current differences, then the measurement precision improves, but the circuit becomes more sensitive to saturation from large input signals
Solution Approach 1:
The patent implements dynamic range extension by allowing the TIA output to swing into negative voltages when the differential input current is negative. This dynamic behavior enables the use of higher TIA gain values without saturation, as the output voltage range is effectively doubled compared to single-ended operation. The polarity of the output voltage indicates which input current is larger, preserving measurement precision while increasing saturation resistance.
3Loss of information
If two separate digital measurements are transmitted, then the complete information is conveyed, but the RF transmission power consumption increases and communication security is reduced
Solution Approach 1:
The patent merges the transmission of two separate digital measurements into a single A-D conversion operation. By converting the analog sum signal (which contains both magnitude and polarity information representing the two original signals) into a single digital value, the system conveys complete information about both input currents while performing only one RF transmission, thereby reducing power consumption and improving communication security.
4Device complexity
If the ADC dynamic range is limited, then the circuit is simpler, but the resolution for measuring small current differences deteriorates
Solution Approach 1:
The patent changes the parameter being measured by the ADC from individual current magnitudes to the algebraic sum of two current signals. This parameter transformation allows a limited-range ADC to effectively measure a wider dynamic range by utilizing the polarity of the sum signal. When the first current is larger, the sum is positive; when the second current is larger, the sum is negative. This approach maintains circuit simplicity while improving current signal resolution through clever use of the ADC's full voltage range.
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
This approach allows for 100% utilization of ADC dynamic range for the signal difference, reduces power consumption, and compensates for environmental offsets, achieving high accuracy and resolution with fewer transistors and less area.
Implementation Method 1
a differential capacitive transimpedance amplifier having: a first capacitance and a first switching element connected in parallel to the negative input port and a first output port of the differential capacitive transimpedance amplifier
Data Source
Figure 1~3
Figure 4~6
AI summary
The present invention relates to a circuit for performing arithmetic operations comprising a differential capacitive transimpedance amplifier (CTIA) and a cross-multiplexer, wherein the cross multiplexer forwards the current to be integrated out of a plurality of current sources either to the positive input port of the differential CTIA for positive integration in direct mode or to the negative input port of the differential CTIA for negative integration in reverse mode.