Dynamic Capacitor Selection for Consistent ADC Sensing Timing
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Solution Overview
Problem
Conventional in-memory computing components face variability in the time required for internal circuitry to reach sufficient current or voltage values for value storage due to varying currents and voltages from bit lines, leading to inefficiencies in CIM operations.
Innovation Solution
A circuit and method utilizing a global counter, capacitors with dynamically varying capacitance values, and a comparator to ensure consistent and efficient storage of counter values by selecting capacitors based on pre-coded codes, allowing for earlier selection of capacitors with higher capacitance to expedite the charging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional local sensing circuits use fixed capacitors for analog-to-digital conversion, then the circuit structure is simple, but the storage time varies greatly based on current and voltage conditions
Solution Approach 1:
The patent applies dynamics by transitioning from fixed capacitors to dynamically selectable capacitors. The capacitor selector circuitry chooses different capacitors based on pre-coded codes that correspond to different current and voltage conditions, allowing the system to adapt its charging characteristics in real-time to maintain consistent storage timing.
Solution Approach 2:
The patent changes the capacitance parameter dynamically by selecting from multiple capacitors with different capacitance values. This allows the system to optimize the charging time constant (tau = RC) for different operating conditions, ensuring that the analog-to-digital conversion completes within a consistent time frame regardless of variations in bit line currents and voltages.
2Productivity
If capacitors with higher capacitance values are selected, then the charging process is expedited for lower currents, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-coding the codes that specify which capacitors to select based on anticipated current and voltage conditions. This allows the capacitor selection to be made in advance or in synchronization with the sensing operation, ensuring optimal charging speed without adding complex real-time decision-making circuitry.
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 reduces the variability in storage time across different current and voltage conditions, enhancing the efficiency and consistency of CIM operations by ensuring timely storage of counter values.
Implementation Method 1
the selected one or more capacitors configured (i) to receive a charging current in dependence on a bit line current of a selected bit line of the plurality of bit lines, (ii) to store a charge in dependence on the charging current and (iii) to produce a detected voltage (Vc) resulting from the stored charge
Data Source
AI summary
A circuit comprises a plurality of bit lines, a global counter configured to provide a count value, a global reference source, a plurality of capacitors, a comparator, a storage element, and capacitor selector circuitry. The capacitor selector circuitry is configured to select, in dependence on the count value, one or more capacitors from the plurality of capacitors, and wherein the selection of the one or more capacitors is further in dependence on pre-coded codes receivable from an agent separate from the circuit, the pre-coded codes enabling specifying respective first and second sets of the plurality of capacitors as respective one or more capacitors having respective first and second capacitance values, the pre-coded codes further enabling specifying selection of the first set to be performed at an earlier time than selection of the second set, and the second capacitance value is more than the first capacitance value.