SAR ADC Capacitor DAC Layout for Stable High-Rate Sampling
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Solution Overview
Problem
Existing successive approximation AD converters with capacitor DACs face reduced conversion accuracy due to indeterminate potentials in the target wiring during sampling, necessitating an initializing operation that limits the maximum sampling rate.
Innovation Solution
Incorporating a potential fixing switch to stabilize the target wiring potential during sampling, eliminating the need for an initializing operation and enhancing the maximum sampling rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an initializing operation is performed to stabilize target wiring potential, then AD conversion accuracy is improved, but the maximum sampling rate is reduced
Solution Approach 1:
The potential fixing switch performs the initializing operation automatically at the beginning of each sampling period, stabilizing the target wiring potential before the actual sampling occurs. This preliminary stabilization eliminates the need for a separate initializing phase, allowing continuous sampling at maximum rate while maintaining conversion accuracy.
Solution Approach 2:
The potential fixing switch integrates the initializing function into the normal sampling operation flow. By automatically fixing the potential of the target wiring during the sampling process itself, the system performs initialization as part of its regular operation, eliminating the trade-off between accuracy and sampling rate.
2Device complexity
If the target wiring potential is left indeterminate during sampling, then the circuit structure is simplified, but AD conversion accuracy deteriorates
Solution Approach 1:
The potential fixing switch acts as an intermediary element that temporarily stabilizes the target wiring potential during sampling. This switch is connected between the target wiring and a reference potential (VDD or GND), providing the necessary stabilization only when needed, while maintaining circuit simplicity through its minimal presence and automatic operation.
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
Stabilizing the target wiring potential improves AD conversion accuracy and increases the maximum sampling rate by avoiding the need for initializing operations.
Implementation Method 1
a capacitor array (11) and a switch array (12) connected to the capacitor array, the capacitor DAC being configured to cause a charge corresponding to the analog input signal to be stored in each capacitor in the capacitor array by connecting wiring (Ain) to which the analog input signal is applied to the capacitor array via the switch array
Implementation Method 2
a comparator (20) connected to the first comparison wiring and second comparison wiring (WR2) to which a second comparison voltage (V2) is applied, the comparator being configured to compare the first comparison voltage and the second comparison voltage with each other and generate a comparison result signal (SCMP)
Data Source
AI summary
Provided is a successive approximation AD converter circuit that converts an analog input signal into a digital output signal. The successive approximation AD converter circuit includes a capacitor DAC including a capacitor array and a switch array connected to the capacitor array, a comparator connected to first comparison wiring and second comparison wiring, and a control circuit that determines a value of the digital output signal while controlling a state of the switch array. The capacitor array includes a first local array provided between the first comparison wiring and the switch array and a second local array provided between target wiring and the switch array. The capacitor DAC is provided with a scaling capacitor between the target wiring and the first comparison wiring and is provided with a potential fixing switch between the target wiring and the wiring to which the analog input signal is applied.