Multipath Amplifier Architecture for Stable SAR ADC Gain Variation
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Solution Overview
Problem
Designing an amplifier that remains stable with varying open loop gain and bandwidth requirements in a recyclic successive approximation register (SAR) analog-to-digital converter (ADC) is challenging due to fluctuations from cycle to cycle.
Innovation Solution
A multi-stage amplifier architecture with cascaded preamplifiers and output amplifiers, coupled with switches and capacitors, is employed to provide stable feedback paths and auto-zeroing capabilities, allowing for effective resolution of multiple bits per conversion clock cycle while managing closed loop gain changes and capacitive loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional amplifier design is used in a recyclic SAR ADC, then the circuit implementation is simpler, but the amplifier becomes unstable when open loop gain and bandwidth vary from cycle to cycle
Solution Approach 1:
The amplifier is divided into multiple parallel paths (first amplifier path, second amplifier path, third amplifier path) with different gain stages. Each path processes signals with different amplification factors, allowing the system to handle varying gain requirements while maintaining stability through the segmented architecture rather than a single complex variable-gain amplifier.
2Measurement precision
If the open loop gain is increased to improve resolution, then the measurement precision improves, but the bandwidth decreases and stability becomes difficult to maintain
Solution Approach 1:
The system dynamically selects which amplifier path to use based on the required resolution and timing requirements. Switches (first switch, second switch, third switch) enable dynamic reconfiguration of the amplifier paths, allowing the system to adapt between high-gain/low-bandwidth modes for precision and lower-gain/high-bandwidth modes for speed, maintaining optimal performance across different operating conditions.
3Adaptability or versatility
If multiple amplifier paths with different gains are implemented, then the adaptability to varying gain requirements improves, but the device complexity increases
Solution Approach 1:
Multiple amplifier paths share common components such as the input terminals, output terminals, and switching infrastructure. The first preamplifier, second preamplifier, and third preamplifier all connect to the same input/output nodes, and the switches collectively manage signal routing. This multi-functional design allows a single amplifier system to provide multiple gain configurations without requiring completely separate amplifier circuits for each path.
Data Source
AI summary
Because of variations in open loop gain and bandwidth in successive approximate register (SAR) analog-to-digital converters (ADCs), designing amplifiers with the desired characteristics is difficult. Here, a multipath amplifier is provided that accounts for the variations in open loop gain and bandwidth. Preferably, a number of cascaded amplifiers are provided that can auto-zero to account for offset voltages so as to allow the multipath amplifier to be stable over the desired open loop gains and bandwidths.