Two-Stage Ramp ADC for Faster Crossbar Matrix Multiplication
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Solution Overview
Problem
Conventional ramped Analog to Digital Converters (ADCs) are inefficient for high-performance applications like Artificial Intelligence computing due to their slow data conversion speed and high sampling time, especially when implemented in crossbar array circuits, which are required for high-resolution and high-speed matrix multiplication.
Innovation Solution
A two-stage ramp ADC design is implemented in crossbar array circuits, utilizing a transimpedance amplifier, comparator, switch bias set, ramp side capacitor, ramp generator, counter, and memory, with a capacitance ratio of the ramp side capacitor to switch side capacitor of at least three orders of magnitude, enabling coarse and fine conversion stages to determine input signal voltage, thereby reducing the total comparison cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional single-slope ramp ADC is used in crossbar array circuits, then the circuit structure remains simple, but the data conversion speed is slow and sampling time is long
Solution Approach 1:
The ADC conversion process is divided into two distinct stages: a first stage that determines the most significant bits (MSBs) using switch bias voltages, and a second stage that determines the least significant bits (LSBs) using a ramp voltage. This segmentation allows parallel processing of different bit groups, significantly reducing total conversion time while maintaining conversion accuracy.
Solution Approach 2:
The first stage of conversion is performed in advance by comparing the input voltage against predefined switch bias voltages to determine the MSBs. This preliminary determination narrows down the voltage range before the second stage begins, allowing the ramp generator to start earlier and reducing the overall sampling time required for high-resolution conversion.
2Measurement precision
If higher resolution is achieved in conventional ramp ADC, then more comparison cycles are required, but this increases sampling time and reduces computing speed
Solution Approach 1:
The 8-bit or higher resolution conversion is segmented into two stages: the first stage determines the MSBs (e.g., 4 bits) by comparing against switch bias voltages, and the second stage determines the LSBs (e.g., 4 bits) using the ramp voltage. This segmentation allows high resolution to be achieved without proportionally increasing total comparison cycles, as the first stage quickly eliminates large voltage ranges.
Solution Approach 2:
The system changes the voltage comparison parameter dynamically: in the first stage, fixed switch bias voltages are used for rapid MSB determination, while in the second stage, a time-varying ramp voltage is used for precise LSB determination. This parameter change strategy optimizes the balance between conversion speed and resolution accuracy.
3Measurement precision
If a single comparator is used for high-resolution conversion, then conversion accuracy is maintained, but conversion time increases significantly
Solution Approach 1:
The conversion process is segmented into two parallel-comparable stages: the first stage uses the comparator to determine MSBs against switch bias voltages, and the second stage uses the comparator to determine LSBs against the ramp voltage. By segmenting the conversion tasks, the total conversion duration is reduced while maintaining overall conversion accuracy through the combined results of both stages.
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 design significantly increases sampling speed and reduces interference, achieving higher resolution and faster data conversion without the need for complex integrated circuits, making it suitable for high-speed, high-accuracy, low-power, and small-area applications in AI computing and neuromorphic computing.
Implementation Method 1
a transimpedance amplifier configured to convert an input signal from current to voltage
Implementation Method 2
a ramp generator connected to the comparator via the ramp side capacitor, wherein the ramp generator is configured to generate a ramp signal
Implementation Method 3
the MSBs (Most Significant Bits) of the input signal are determined based on a coarse conversion comparison between the voltage of the input signal and a voltage of reference voltages generated via the first switch, the second switch, and the third switch
Implementation Method 4
a switch side capacitor in parallel with the switch bias set; a ramp side capacitor in parallel with the switch bias set, wherein a capacitance of the ramp side capacitor is higher than that of the switch side capacitor for more than or equal to 3 orders of magnitude
Data Source
AI summary
Technologies relating to implementing two-stage ramp ADCs in crossbar array circuits for high performance matrix multiplication are disclosed. An example two-stage ramp ADC includes: a transimpedance amplifier configured to convert an input signal from current to voltage; a comparator connected to the transimpedance amplifier; a switch bias set connected to the comparator; a switch side capacitor in parallel with the switch bias set; a ramp side capacitor in parallel with the switch bias set; a ramp generator connected to the comparator via the ramp side capacitor, wherein the ramp generator is configured to generate a ramp signal; a counter; and a memory connected to the comparator, wherein the memory is configured to store an output of the comparator.