Differential ADC Reset Switching for Faster Sample-and-Hold
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Solution Overview
Problem
Existing electronic circuits with sample and hold circuits and analog to digital converters face challenges in achieving high-speed operation due to capacitive loading and inter-sample interference, which slows down the conversion process and increases power consumption.
Innovation Solution
The implementation of a control circuit that selectively couples the outputs of a differential amplifier to a circuit node of the analog to digital converter, allowing for a short circuit phase without a large switch, minimizing capacitive loading and reducing inter-sample interference by using feedback switches and demultiplexing circuitry to alternate polarity connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large switch is used to short circuit the outputs of the differential amplifier for reset, then inter-sample interference is reduced, but capacitive loading increases and operational speed decreases
Solution Approach 1:
The reset function is segmented from the main signal path by using separate feedback switches that operate independently during reset phases. This allows the differential amplifier outputs to be reset without requiring a large switch in the main signal path, thereby reducing capacitive loading while maintaining inter-sample interference reduction.
Solution Approach 2:
Feedback switches are introduced as intermediary elements that provide a dedicated reset path from the output to the input of the differential amplifier. These switches enable reset functionality without requiring large switches in the main signal path, thus reducing capacitive loading while maintaining reliability.
2Reliability
If the differential amplifier is continuously active to maintain output voltages, then inter-sample interference is reduced, but power consumption increases
Solution Approach 1:
The differential amplifier operates periodically rather than continuously, with feedback switches activating only during specific reset phases. This periodic operation maintains output voltage control and reduces inter-sample interference while significantly reducing average power consumption compared to continuous operation.
Solution Approach 2:
The feedback mechanism allows the differential amplifier to self-regulate its output voltages during active phases without requiring continuous external control. The amplifier automatically maintains proper voltage levels during conversion phases while the feedback switches provide periodic reset, reducing overall power consumption.
3Productivity
If switching speed is increased to improve conversion speed, then productivity is improved, but inter-sample interference increases
Solution Approach 1:
The feedback switches are activated in advance during dedicated reset phases before the next sampling and conversion cycle begins. This preliminary reset action ensures that any inter-sample interference from previous cycles is eliminated before high-speed switching occurs, allowing fast conversion without increasing interference.
Solution Approach 2:
The feedback switches create a closed-loop reset mechanism that actively compensates for inter-sample interference. By monitoring output voltages and providing feedback to reset the differential amplifier inputs, the system can maintain high switching speeds while continuously suppressing inter-sample interference through the feedback control mechanism.
Data Source
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AI summary
Analog to digital conversion is performed by sampling an input voltage followed by AD conversion of the sampled voltage. In the sample and hold circuit a differential amplifier output voltage is generated between the first and second output of a differential amplifier in response to the sampled input voltage. A conversion polarity is selected by connecting the one output or the other of the differential amplifier to a circuit node in an AD conversion circuit using a first or second switch. These switches from both outputs of the differential amplifier to the same circuit node of the AD conversion circuit are both made conductive simultaneously prior to making the selected one of the first and second switch conductive. In this way, the amplifier output voltage is reset without requiring a dedicated switch just for this purpose.