SAR ADC Reference Line Impedance Control for Noise Isolation
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Solution Overview
Problem
In charge redistribution type successive approximation AD converters, noise propagation due to reference voltage fluctuations affects the accuracy of other circuits sharing the signal line, particularly during steep changes in current during capacity switching operations, leading to inaccurate operations.
Innovation Solution
Incorporating a variable impedance circuit and a control circuit that adjusts impedance on the signal line between the AD converter and the reference voltage pins, performing redundant comparison operations to determine bit values and controlling impedance levels to suppress noise propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a charge redistribution type successive approximation AD converter is used, then conversion speed is improved, but noise is generated on the signal line due to charge and discharge during capacity switching
Solution Approach 1:
A variable impedance circuit is introduced as an intermediary component between the AD converter and the reference voltage signal line. This circuit mediates the interaction by dynamically adjusting its impedance to isolate the reference voltage line from noise generated during capacity switching, thereby allowing fast conversion while suppressing noise propagation
Solution Approach 2:
The impedance of the variable impedance circuit is dynamically changed based on the operating phase of the AD converter. During capacity switching operations when noise is generated, the impedance is increased to block noise propagation. During other phases, the impedance is reduced to maintain proper reference voltage levels, thus resolving the contradiction between speed and noise
2Measurement precision
If a large capacity switch is performed during upper bit comparison operation, then conversion accuracy is improved, but the change in current becomes steep and large noise is generated on the signal line
Solution Approach 1:
The variable impedance circuit dynamically adjusts its impedance value according to the specific comparison operation phase. During upper bit comparison operations where large capacity switching occurs, the circuit increases its impedance to suppress the steep current change and resulting noise, while maintaining the necessary switching action for accurate conversion
Solution Approach 2:
The noise suppression is applied locally and selectively only during the problematic upper bit comparison operations. The variable impedance circuit provides different impedance characteristics for different operational phases, allowing accurate large-capacity switching when needed while suppressing noise only during the specific phases where it occurs
3Device complexity
If the reference voltage propagates on a shared signal line, then circuit simplicity is maintained, but noise is transmitted to other circuits that share the signal line
Solution Approach 1:
The variable impedance circuit serves as a mediator on the shared signal line, allowing the reference voltage to propagate to multiple circuits while dynamically blocking noise transmission. This maintains the simplicity of using a shared signal line while adding noise isolation capability through impedance control
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 enables accurate operation of AD converters while minimizing interference noise by managing impedance changes and reducing reference voltage fluctuations, ensuring precise bit value determination and reducing errors.
Implementation Method 1
a first variable impedance circuit that is provided on a signal line between the first AD converter and is configured to be able to change the impedance
Data Source
AI summary
A semiconductor device capable of operating accurately while suppressing the propagation of interference noise, a control method for the semiconductor device, and a control program are provided. The semiconductor device includes a first AD converter of a charge redistribution type sequential comparison type that includes a redundant comparison operation in a sequential comparison operation and outputs a first input signal of an analog differential using a reference voltage to a first output signal of digital, a first pin to which the reference voltage is supplied from the outside, a first variable impedance circuit provided on a signal line between the first AD converter and capable of changing impedance, and a first control circuit 10 that controls the impedance of the first variable impedance circuit according to the operating condition of the first AD converter.